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3 High Power SG3525 Pure Sinewave Inverter Circuits

3 High Power SG3525 Pure Sinewave Inverter Circuits

The post explains a 3 powerful yet simple sine wave 12V inverter circuits using a single IC SG 3525. The first circuit is equipped with a low battery detection and cut off feature, and an automatic output voltage regulation feature.

This circuit was requested by one of the interested readers of this blog. Let's learn more about the request and the circuit functioning.

Design#1: Basic Modified Sine

In one of the earlier posts I discussed the pin out functioning of the IC 3525, using the data, I designed the following circuit which is though quite standard in its configuration, includes a low battery shut down feature and also an automatic output regulation enhancement.

The following explanation will walk us through the various stages of the circuit, let's learn them:



As can be witnessed in the given diagram, the ICSG3525 is rigged in its standard PWM generator/oscillator mode where the frequency of oscillation is determined by C1, R2 and P1.

P1 can be adjusted for acquiring accurate frequencies as per the required specs of the application.

The range of P1 is from 100Hz to 500 kHz, here we are interested in the 100 Hz value which ultimately provides a 50Hz across the two outputs at pin#11 and Pin#14.

The above two outputs oscillate alternately in a push pull manner (totem pole), driving the connected mosfets into saturation at the fixed frequency - 50 Hz.

The mosfets in response, "push and Pull the battery voltage/current across the two winding of the transformer which in turn generates the required mains AC at the output winding of the transformer.

The peak voltage generated at the output would be anywhere around 300 Volts which must adjusted to around 220V RMS using a good quality RMS meter and by adjusting P2.

P2 actually adjusts the width of the pulses at pin#11/#14, which helps to provide the required RMS at the output.

This feature facilitates a PWM controlled modified sine waveform at the output.

Automatic Output Voltage Regulation Feature

Since the IC facilitates a PWM control pin-out this pin-out can be exploited for enabling an automatic output regulation of the system.

Pin#2 is the sensing input of the internal built in error Opamp, normally the voltage at this pin (non inv.) should not increase above the 5.1V mark by default, because the inv pin#1 is fixed at 5.1V internally.

As long as pin#2 is within the specified voltage limit, the PWM correction feature stays inactive, however the moment the voltage at pin#2 tends to rise above 5.1V the output pulses are subsequently narrowed down in an attempt to correct and balance the output voltage accordingly.

A small sensing transformer TR2 is used here for acquiring a sample voltage of the output, this voltage is appropriately rectified and fed to pin#2 of the IC1.

P3 is set such that the fed voltage stays well below the 5.1V limit when the output voltage RMS is around 220V. This sets up the auto regulation feature of the circuit.

Now if due to any reason the output voltage tends to rise above the set value, the PWM correction feature activates and the voltage gets reduced.

Ideally P3 should be set such that the output voltage RMS is fixed at 250V.

So if the above voltage drops below 250V, the PWM correction will try to pull it upward, and vice versa,  this will help to acquire a two way regulation of the output,

A careful investigation will show that the inclusion of R3, R4, P2 are meaningless, these may be removed from the circuit. P3 may be solely used for getting the intended PWM control at the output.

Low Battery Cut-of Feature

The other handy feature of this circuit is the low battery cut off ability.

Again this introduction becomes possible due to the in built shut down feature of the IC SG3525.

Pin#10 of the IC will respond to a positive signal and will shut down the output until  the signal is inhibited.

A 741 opamp here functions as the low voltage detector.

P5 should be set such that the output of 741 remains at logic low as long as the battery voltage is above the low voltage threshold, this may be 11.5V. 11V or 10.5 as preferred by the user, ideally it shouldn't be less than 11V.

Once this is set, if the battery voltage tends to go below the low voltage mark, the output of the IC instantly becomes high, activating the shut down feature of  IC1, inhibiting any further loss of battery voltage.

The feedback resistor R9 and P4 makes sure the position stays latched even if the battery voltage tends to rise back to some higher levels after the shut down operation is activated.

Parts List

All resistors are 1/4 watt 1% MFR. unless otherwise stated.

R1, R7 = 22 Ohms
R2, R4, R8, R10 = 1K
R3 = 4K7
R5, R6 = 100 Ohms
R9 = 100K

C1 = 0.1uF/50V MKT
C2, C3, C4, C5 = 100nF

C6, C7 = 4.7uF/25V
P1 = 330K preset

P2---P5 = 10K presets

T1, T2 = IRF540N

D1----D6 = 1N4007

IC1 = SG 3525

IC2 = LM741

TR1 = 8-0-8V.....current as per requirement

TR2 = 0-9V/100mA Battery = 12V/25 to 100 AH

The low battery opamp stage in the above shown schematic could be modified for a better response as given in the following diagram:

Here we can see that pin3 of the opamp now has it's own reference network using D6 and R11, and does not depend on the reference voltage from the IC 3525 pin16.

Pin6 of the opamp employs a zener diode in order to stop any leakages that might disturb pin10 of the SG3525 during its normal operations.

R11 = 10K
D6, D7 = zener diodes, 3.3V, 1/2 watt

Another Design with Automatic Output Feedback Correction

Circuit Design#2:

In the above section we learned the basic version of IC SG3525 designed to produce a modified sine wave output when used in an inverter topology, and this basic design cannot be enhanced to produce a pure sinewave waveform in its typical format.

Although the modified squarewave or sinewave output could be OK with its RMS property and reasonably suitable for powering most electronic equipment, it can never match the quality of a pure sinewave inverter output.

Here we are going to learn a simple method which could be used for enhancing any standard SG3525 inverter circuit into a pure sinewave counterpart.

For the proposed enhancement the basic SG3525 inverter could be any standard SG3525 inverter design configured to produce an modified PWM output. This section is not crucial and any preferred variant could be selected (you can find plenty online with minor differences).

I have discussed a comprehensive article regarding how to convert a square wave inverter to a sinewave inverter in one of my earlier posts, here we apply the same principle for the upgrade.

How the Conversion from Squarewave to Sinewave Happens

You might be curious to know regarding what exactly happens in the process of the conversion which transforms the output into a  pure sinewave suitable for all sensitive electronic loads.

It is basically done by optimizing the sharp rising and falling square wave pulses into a gently rising and falling waveform. This is executed by chopping or breaking the exiting square waves into number of uniform pieces.

In the actual sinewave, the waveform is created through an exponential rise and fall pattern where the sinusoidal wave gradually ascend and descend in the course of its cycles.

In the proposed idea, the waveform is not executed in an exponential, rather the square waves are chopped into pieces which ultimately takes the shape of a sinewave after some filtration.

The "chopping" is done by feeding a calculated PWM to the gates of the FET via a BJT buffer stage.

A typical circuit design for converting the SG3525 waveform into a pure sinewave waveform is shown below. This design is actually an universal design which may be implemented for upgrading all square wave inverters into sinewave inverters.

Warning: If you are using SPWM as the input, then please replace the lower BC547 with BC557. Emitters will connect with the buffer stage, Collector to Ground, Bases to SPWM Input.

As may be in the above diagram, the lower two BC547 transistors are triggered by a PWM feed or input, which causes them to switch according to the PWM ON/OFF duty cycles.

This in turn rapidly switch the 50Hz pulses of the BC547/BC557 coming from the SG3525 output pins.

The above operation ultimately force the mosfets also to turn ON and OFF number of times for each of the 50/60Hz cycles and consequently produce a similar waveform at the output of the connected transformer.

Preferably, the PWM input frequency should be 4 times more than the base 50 or 60Hz frequency. so that each 50/60Hz cycles are broken into 4 or 5 pieces and not more than this, which could otherwise give rise to unwanted harmonics and mosfet heating.

PWM Circuit

The PWM input feed for the above explained design can be acquired by using any standard IC 555 astable design as shown below:

IC 555 pwm with pot and 1N4148

This IC 555 based PWM circuit can be used for feeding an optimized PWM to the bases of the BC547 transistors in the first design such that the output from the SG3525 inverter circuit acquires an RMS value close to mains pure sinewave waveform RMS value.

Using an SPWM

Although the above explained concept would greatly improve the square wave modified output of a typical SG3525 inverter circuit, an even better approach could be to go for an SPWM generator circuit.


In this concept the "chopping" of each of the square wave pulses is implemented through a proportionately varying PWM duty cycles rather than a fixed duty cycle.

I have already discussed how to generate SPWM using opamp, the same theory may be used for feeding the driver stage of any square wave inverter.

A simple circuit for generating SPWM can eb seen below:

generating sine pulse width modulation or SPWM with opamp

Using IC 741 for Processing SPWM

In this design we see a standard IC 741 opamp whose input pins are configured with a couple of triangle wave sources, one being much faster in frequency than the other.

The triangle waves could be posibly extracted from a standard IC 556 based circuit, wired as an astable, as shown below:

triangle wave from IC 556

This forces the opamp to compare the two coinciding peaks of the waveforms and generate SPWM or sinewave PWM consisting of a proportionately widening and narrowing PWMs in each cycle.

When this optimized PWM is fed to the first circuit design causes the output from the transformer to produce a further improved and gentle sine waveform having properties much identical to a standard AC mains sine waveform.

However even for an SPWM, the RMS value will need to be correctly set initially in order to produce the correct voltage output at the output of the transformer.

Once implemented one can expect a real sinewave equivalent output from any SG3525 inverter design or may be from any square wave inverter model.

If you have more doubts regarding SG3525 pure sinewave inverter circuit you can feel free to express them through your comments.

 UPDATE

A basic example design of a SG3525 oscillator stage can be seen below, this design could be integrated with the above explained PWM sinewave BJT/mosfet stage for getting the required enhanced version of the SG3525 design:

Simple IC SG3525 inverter configuration

Complete circuit diagram and PCB layout for the proposed SG3525 pure sine wave inverter circuit.

Courtesy: Ainsworth Lynch

SG3525 chopped inverter using IC 555
PCB design of SG3525 inverter circuit

Design#3: 3kva Inverter circuit using the IC SG3525

In the previous paragraphs we have comprehensively discussed regarding how an SG3525 design could be converted into an efficient sinewave design, now let's discuss how a simple 2kva inverter circuit can be constructed using the IC SG3525, which can be easily upgraded to sinewave 10kva by increasing the battery, mosfet and the transformer specs.

The basic circuit is as per the design submitted by Mr. Anas Ahmad.

The explanation regarding the proposed SG3525 2kva inverter circuit can be understood from the following discussion:

hello swagatam, i constructed the following 3kva 24V inverter modified sine wave (i used 20 mosfet with resistor attached to each, moreover i used center tap transformer and i used SG3525 for oscillator).. now i want to convert it to pure sine wave, please how can i do that?

Basic Schematic

My Reply:

Hello Anas,

first try the basic set up as explained in this SG3525 inverter article, if everything goes well, after that you can try connecting more mosfets in parallel.....

the inverter shown in the above daigram is a basic square wave design, in order to convert it to sine wave you must follow the steps explained below The mosfet gate/resistor ends must be configured with a BJT stage and the 555 IC PWM should be connected as indicated in the following diagram:

SG3524 with BJT buffer stage

Regarding Connecting parallel mosfets

ok, i have 20 mosfet(10 on lead A, 10 on lead B), so i must attached 2 BJT to each mosfet, that's 40 BJT, and likewise i must connect only 2 BJT coming out from PWM in parallel to the 40 BJT? Sorry am novice just trying to pick up.

Answer: 
No, each emitter junction of the respective BJT pair will hold 10 mosfets...therefore you will need only 4 BJTs in all....

Using BJTs as Buffers

1. ok if i may get you right, since you said 4 BJTs, 2 on lead A, 2 on lead B, THEN another 2 BJT from the output of PWM, right?
2. am using 24 volt battery hope no any modification to the BJT collector terminal to the battery?
3. i have to use variable resistor From oscillator to control the input voltage to the mosfet, but i don't know how i will go about the voltage that will go to the base of the BJT in this case, what will i do so that i want end up blow up the BJT?

Yes, NPN/PNP BJTs for the buffer stage, and two NPN with the PWM driver.
24V will not harm the BJT buffers, but make sure to use a 7812 for stepping it down to 12V for the SG3525 and the IC 555 stages.

You can use the IC 555 pot for adjusting the output voltage from the trafo and set it to 220V. remember your transformer must be rated lower than the battery voltage for getting optimum voltage at the output. if your battery is 24V you can use an 18-0-18V trafo.

Parts List

IC SG3525 Circuit 
all resistors 1/4 watt 5% CFR unless otherwise specified
10K - 6nos
150K - 1no
470 ohm - 1no
presets 22K - 1no
preset 47K - 1no
Capacitors
0.1uF Ceramic - 1no
IC = SG3525
Mosfet/BJT Stage 
All mosfets - IRF540 or any equivalent Gate resistors - 10 Ohms 1/4 watt (recommended)
All NPN BJTs are = BC547
All PNP BJTs are = BC557
Base Resistors are all 10K - 4nos
IC 555 PWM Stage 
1K = 1no 100K pot - 1no
1N4148 Diode = 2nos
Capacitors 0.1uF Ceramic - 1no
10nF Ceramic - 1no
Miscellaneous IC 7812 - 1no
Battery - 12V 0r 24V 100AH Transformer as per specs.

SHARING IS CARING!


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!



619 thoughts on “3 High Power SG3525 Pure Sinewave Inverter Circuits”


  1. Howdy, Friend! Interested to Learn Circuit Designing? Let's Start Discussing below!
  2. Please sir I need a simple schematic diagram of 3kv inverter, because that one in this post have 2 diagrams and it is confusing me.

  3. Hello teacher, first let me say a big thanks to you, Three ★** 4 u👌 I build #3design 3kva without any problem, i use x10 IRF540N 48V 0 48V transformer 12v 100ah battery x4 but i don’t know how to calculate how many MOSFET i should use. Please teacher i want to know if i could build a smaller watts like 300w, 500w to 1000w and how to make the change, if it can be done, what should i do?

  4. Thanks for more diagrams can i buy pcb circuit (sine wave)from you now so how can communicate to you cause i need pure sine diagrams with sg3525 chip thanks

    • Thanks selemani, glad you liked my diagrams, however I am sorry presently I am unable to provide PCB designing help due to work load, I hope you will understand!

  5. okay sir pin 11 =6.03v and pin 14 = 6.03v,,,,do you meant that I should make the transformer primary 6-0-6 and the secondary output 220v? I already made my transformer 9-0-9 and 0-220..I want to make 1000w inverter…

    • Sorry Sunshine, there’s a slight confusion. Since duty cycle is 50% for each cycle, 6V corresponds to 100% duty cycle for each output, for a 12V battery….so your trafo should be 12-0-12V, but 9-0-9 is also OK.

      Now make sure the current of the battery side of the trafo is high at least 10 amps.

      • God bless you abundantly sir for your I have built this circuit 3 times without any problems, but I’m building another one and if I reduce p2 it gives voltage of about 100v but if I increase it it damage 3525 and if I pls sir I need your help.

        • Thank you Kayode, can you please show me exactly which 3525 circuit are you building?
          P2 is only for setting the reference value for the error opamp (which has a high input impedance), it cannot cause any damage to the IC. It seems your IC is duplicate or is a faulty one.

          • tnks for the response my tutor, what i noticed is that even when all the connection and callibration of the inverter parameters is done and the inverer is working ,when i remove the battery terminal and put it back ,it sparks and when it sparks the sg3525 is dead, replacing it againg the inverter starts to work. im just kind of confused, i added an electrolytic cap to filter the input to the osc and increased the gate resistor with 1k ohms in series with each signal from#11 and #14 it gives better results but i doubt its good functionality because of the way i see its differnt from others i did, but maybe its the ic. ill change it sir, also the auto regulation principle is a litle bit confusing because i did it and its auto reg was about 10% efficient, pls sir can you ellaborate on the auto reg? tnks and god bless you

            • Hi Kayode, connect the supply voltage to the IC through a 100 ohm 1 watt resistor, and make sure to connect a 100uF/25V across the supply pins of the IC, and also add a 12V 1 watt zener across these supply pins. this will prevent your IC from blowing repeatedly.

            • Tnks sir, I’ll do that and give you the feedback ,
              1. Pls must the c1 be mkt type or can we use the ceramic disc type?
              2 pls is the auto correction for maintaining the set value so that it doesn’t go beyond or below n because , I don’t have a stable voltage, it drops while increasing load, to about 170. . Pls what do I do to get a stable 230v.?
              3. The output of the 741 ic shuts down the 3525 gradually thus making the output of the inverter gets lower slowly till it dies, I have used the 4007 diode forward bias to the 3525 #10, all is about the first design, tnks sir, awaiting your reply .

            • Kayode,
              1) C1 should be MKT preferably, although ceramic will also work.
              2) If your output is decreasing with load, it means your battery current is insufficient to handle the load. The auto correction can never increase the output. The auto correction can keep the output constant only as long as the load is within the battery limits.
              3) The operation is correct, the output will go down slowly when pin10 is held high continuously

  6. good day sir,, engr. I built the 3rd circuit above..there is output voltage from ic, I connected MOSFETs with 12v ups transformer but the output voltage from the transformer can’t power any load,,, okay I made the battery 24v it powers 100w bulb if I put another load the voltage comes lower pls help..my battery is okay…

    • Hi Sunshine, please measure the DC voltage at pin#14 or pin#10 with respect to ground. The transformer primary rating should be ideally equal to this value. Randomly changing battery or transformer can damage something in the circuit. Also the current delivering capacity of the transformer should be high, above 10 amps.

  7. good evening sir, thanks for your post, please sir , I built the above inverter I mean that of Anas though I used all the modifications built when ever I connect transformer the MOSFETs get heated immediately, I have damage lots of MOSFETs and I have checked for errors but can’t fine any, though I didn’t consider the resistors wattage. I used20k preset instead of 22k, 50k instead of 47k and I used a 650 watts ups transformer and irf3205 MOSFETs please I need your help

    • Hi eric, please try the 3rd circuit in its basic form, once its working is confirmed then you can upgrade the mosfet stage with the BC547/BC557 stage and more parallel mosfets.

      If still the mosfets burn then the problem could be somewhere in your circuit layout.

      Resistor wattage or slight preset value changes should not have any effect on the working of the circuit

  8. Good morning Sir…thanks for your regard, question about the transformer, I’m using 200w super Master stabilizer’s transformer,guage20 for 220v o/p side and guage12 for I/p side…..should I wind the input side 9-0-9. OR 12-0-12..and separate winding for the battery charger like 18v…for 12v Inverter… Or can you direct me here, like the turns for primary side and secondary, what wattage could such transformer give? Thanks Please don’t be upset for my disturbance.

    • Hi Sunshine, the winding for inverter operation can be 9-0-9 for a 12V battery, for the charger you can add a separate 0-12V winding, having 10 times lower current specs than the battery Ah rating.

  9. Thanks so much I really appreciate.. God bless you..i will try this with the pure sine wave conversion system…I like your company..

  10. Okay thanks.. Please help me with any good inverter circuit that can power small refrigerator.. May God reward you with good thongs

  11. good morning Sir… u have not replied my text..

    good day ENGR. thanks so much for your love and help…. I built the Inverter u Posted using SG 3524 pwm…is working the output  voltage 220vac but is not stable, if I vary it sometimes it will be stable sometimes it will be blinking… what could be the issue?…. please I want to build Inverter that can power refrigerator…which circuit can I use please help..thanks so much my regard to your company friends and families.

    • Hello Sunshine, if the output is fluctuating rapidly then there could be some problem with the configuration or one of the components, it can be difficult to troubleshoot it without a practical testing

  12. Hello my friend, I build one of your inverter circuit with 4047 ic. And it works perfectly. I want add this feature that will switch off the inverter when battery is drain to 9 or 10 volts.

  13. I meant any way to use the freezer with the 720w panels and bad 36v batteries and the inverter. I even used stabilizer with it, still it didn’t work

  14. Thanks for being resourceful sir. Please presently I am using 36v/2.5kva inverter with solar panels, which used to carry my freezer, but now the batteries are bad, is there anyway I can still use the freezer, only my fridge is working, I am totally off grid.

    I have tried using your triac circuit for inductive loads, not working.

    At peak sunlight, still not working. Freezer is new

    Any advice please.

    • Thanks Grace, Can you please specify your exact requirement? Are you trying to control 36V with a triac? Triacs will never work with DC.

  15. I meant how to build 120v/10kva inverter using 10batteries. Most importantly the smps power supply for the oscillator section, stepdown 120v to 12v for the oscillator

    • hi sir swagatam, i want to built a project inverter using 555 and 4017 with a transformer of single 12v/220v rated 1000va, do you have any circuit what u call them full bridge or h bridge circuit. thanks

        • thank you sir, may i ask? how about the article you post about the SG3525A with a full bridge power schematics? i have read it. is it possible to implement? or have no choice but to use the the recommended ICs. i have a EGS002 pure sine wave driver. thanks

          • Hi TCWS, I got the design from one of the forums, I have not tested it practically. Therefore I won’t recommend it to a newcomer. The full bridge drivers are foolproof and therefore there’s minimum risk in using them.

  16. Good day sir, when I put my fan(50w) to speed 1 and 2, it works fine with inverter(2.5kva), but at speed 3 the inverter blew. But speed 3 is working fine with public utility, please what could be wrong

  17. Hi Swagatam,
    Longtime friend,
    This article is well presented, though I have different but related request, I want to build an inverter using the same chip sg3525 but I’m using ferrite core instead of iron core, using basic circuits I manage to get 210ac at 30kHz, how can I use another Sg3525 to get 220ac at 50Hz!?
    Preferably with automatic output voltage regulations.

    My regards to you all.
    Greetings from Tanzania 🇹🇿

    • It’s for chopping the mosfet gate frequency into smaller blocks, so that the RMS waveform of the output can be set appropriately

      • I checked the THD of the inverter design using analyser, I got 8.8% as compared with 2.5% of the utility. Can I call it pure sine wave or what.

        • what kind of waveform are you getting?? If you can optimize a correct waveform and make it close to the utility waveform then the THD will also improve. You can do it by adding LC filters at the output

  18. Sir i got a 200w inverter wich usins sg3524 i modified it by hooking up the feedback for rms correction. The problem is when i connect a 16w led the output voltage drops from 220 to 212 if i increase load it keeps droping. Without load if i increase input voltage the output is not increasing meaning its only working on overvoltage not on undervoltage. Does this ic feedback work on voltage drop or am missing somethng. I know schematic is worth posting but dont have it.

    • Hi Francis, what is the Ah rating of the battery? Please check with ammeter the current consumption of the system by connecting in it series with the battery positive, also check whether the battery voltage is dropping or not. If the battery voltage is dropping will indicate that your system is drawing over current, or your battery is not good, and this may be causing the output to drop.

      Feedback will not work for over load or over current situation if it exceeds the transformer or battery limits.

  19. Hello Sir, please I have an issue with my inverter automatic voltage regulator made 7 months ago using an optocoupler. The issue is that for a week now it’s not regulating well any longer, I have to reset it manually, it may work fine for two days then I reset it again. I have tried replacing it but same result. Thanks .

  20. good day sir. I have problem with my SG3525A inverter feedback. my feedback is from the output of the transformer, through 280k resistor, through a diode, through one leg of 50k VR to pin 1. before I connect the feedback, the output voltage was 220v. but after I connect the feedback, the output voltage reading comes down to 0v with the inverter making a tickle tickle sound( though not loud). I tried adjusting the VR but the voltage does not respond. Pls help because I need this output voltage stabilizer seriously.

  21. Hello, I used a transformer of 12-0-12v rating to design an inverter using your 555 pwm model with Sg3524 ic, I thought I would get above 300v output at the transformer but I got 220v. Is it normal.

    • Please check the DC voltage at the gate of the mosfet, your transformer must be rated at this voltage to get 310V out. And preferably this DC level must be be equal to battery voltage divided by 1.41.

  22. good day sir. thanks for your previous response. sir, can I use sg3525 square wave inverter to power a freezer. will it have any bad effect on the freezer? thanks.

  23. thanks for all your reply . I think I am learning. sir, I used a 5000w stabilizer transformer to build sg3525A inverter using 6 irf260 in all. how can I know the power of my inverter. I only have digital and analog multimeter. can the output be up to 1500w?

    • Abbey, if it is a 5000 watt then you must get 5000 watts from it, you can check it practically by connecting appropriately rated loads to the inverter and check whether voltage drops or not, the load should work without dropping the voltage by much

  24. sir, I don’t understand your last statement” MAKE SURE YOUR TRANSFORMER ALSO IS RATED AT THIS 50% LESS RATING AT THE PRIMARY SIDE”. Pls can you explain better? thanks.

      • The correct value should be 12 / 1.41 = 9 approximately. So adjust the PWM to get 9V across the output pins of the IC, and select a transformer with 9-0-9V rating at the primary side.

    • you can the check average DC voltage on the output pins of SG3525 while adjusting the pwm until it is almost 50% of the supply voltage, this will hopefully fix the most favorable modified waveform for your circuit…make sure your transformer also is rated at this 50% less rating at the primary side.

  25. good day sir. thanks for all your post. Pls is the first circuit square wave or modified sine wave? if the last design uses sg3525 and it is square, what make the first circuit to be modify sine wave. is sg355A the same to sg3525?

  26. well done sir. Pls is the output from design1 modify sine wave or square wave. I am somehow confuse. since the last design using SG325 is said to be square wave I think the first design also suppose to be square. what make the difference. is SG3525A the same with SG535. thanks.

    • Thanks Abbey, for a modified version you must have the PWMs adjusted such that each block is followed by a gap or a “dead time” meaning it should be one square block then a “null” then the next square block and again another null and so on. This waveform when dumped into transformer winding will try to implement a sine wave like waveform.

      In any SG3525 when you adjust the PWM feature to do the above then it becomes a modified sinewave. So it just depends how you are adjusting this PWM structure through the given pot.
      If this pot is adjusted to produce full square waves then it is no longer a modified sinewave rather a simple square wave.

  27. Hello sir, I actually built the above inverter circuit using ic sg3524 and 555 timer as the sine wave generator. I feed the 555 timer stage with 5v beside 8v fed to the ic sg3524. However, the pwm from ic sg3524 is being blocked by the collectors of the bc547 transistors at the bases of the power stage transistors. The question must sg3524 and 555 timer ICs have the same voltage feed or could there be something else?

    • Chinomso, the lower two BC547 are wired to chop the mosfet gate 50Hz pulses into smaller sections as per the PWM rate, …..it won’t block anything.

      IC 555 can work comfortably with all voltages between 5V and 15V, so no problem with 5V…still you can use 8V for the IC 555 also to clear all doubts

  28. Hi Swag, I have question on the 2 pure sine inverters I made. First, a 2kva/24v with trafo using 12swg in the primary side and 18swg on secondary with adequate filter capacitor 5uf, it carries my freezer easily even at 5% battery level

    However, I made a 3.5kva/36v with trafo using 12.5 swg primary and 16swg secondary even with 32uf filter capacitor it could not carry same freezer at 40% battery level but carries it at 75% or more battery level.

    Sir,what could be responsibl for this low power bigger trafo pure sine inverter(according to your design)that could not carry much load. Thanks Chief.

  29. Hello enginner , Secondly we all understand that technologies have reached its peak, such that it is like morden inovations principles are trying to disagree with early lay down principles upon which many have built their knowledge. Please my questions. I have seen from a blogger from Indonensia who display a pure sine power inverter with frequencies, one is after building gives 77hz ,second 32 hz.Which from his videos he used induction machines like electric driller, fridge,water pump,set up table computer and eletric stove. I am not quiet at ease with it. I know please globally two grid frequencies 50 & 60hzs please your advice.

    • Ekoe, the frequency of a pwm based inverter must be measured and confirmed using an oscilloscope, a multi-meter can give misleading results.

  30. Hi Swagatam, I want you once again that you trow more light on the concepts of choosing transformer and power transistor to a paticulation power inverter oscilation circuit to obtain a desired power. Please consider me, am still not getting hold on this fundamental principles.

    • Hi Ekoe, there’s nothing complicated in it, just divide the maximum intended load wattage with the battery voltage and get the amp value, then make sure the transformer’s and mosfet’s V and I rating are higher than these acquired value

  31. Hi sir, I use copper wire for my MOSFET cascade but when the MOSFETs got burnt due to any reason, and I replace the MOSFETs with same quoted Copper with the black soot from the burnt MOSFETs , the MOSFETs blow again until I change the copper wire. Then no more MOSFETs burning and the inverter is working fine.

          • Thanks Sir, please why is my built inverter gets voltage stable at 220v, 61hz, what could be factors for the 61hz frequency and how can I make it 50hz.

            • Hi Tinuke, please measure the frequency across the output pins of the IC, do this by disconnecting the mosfets from the IC, confirm whether it is 50Hz or not….

            • Thanks it is better after several tweaking I now got 52hz, please what is the size of Ac output capacitor can I use for 5kva/48v because the combination you gave from the redirected page, is not efficient.

            • I am glad you could get the right frequency tinuke, however I am sorry, I do not have any other calculations other than what I suggested you in the referred page.

            • Well done Swagtagam, please how can I set the spwm or pwm (comparing circuits ) preset correctly to get pure sine wave without an oscilloscope because I turned the preset to Max and min without obvious difference.

            • Tinuke, there’s no way to confirm a sine waveform without using an oscilloscope, but to some extent it can be verified through a multimeter by checking the output of the transformer. If the voltage varies in response to PWM variations that would confirm that the PWM function is working.

            • Thanks, I checked the spwm output, it varies as I turned the preset, does that mean it is working.

      • Thanks for your response, I have sorted out the wave. It’s working great. Between modified and pure sine wave I made using your circuits, the two inverters carried the freezer, but the pure sine worked smoother but the two required thesame output filter.

        I thought pure wave inverter will require lesser filtering to carry the freezer. Please educate me

        • Great, I am glad you could sort it out, the filter capacitor or inductor values can be experimented manually…. but only with the help of a oscilloscope

          • Hello sir, I checked the waveform using goldwave software for the waveform looked the same for the three-modified inverter, pure sine wave inverter I built at 50hz and the public utility power supply. They all produced sine wave. But at extreme of the preset value for pwm of pure inverter and at 51hz upward for the modified inverter, the waveform was poor.

            I want to ask why did the modified inverter produced same good sine wave as the pure inverter and the utility. Thanks for your enlightenment.

            • Tinuke, the Goldwave software is actually designed for analyzing music frequencies, I am not sure whether it will be able to check an inverter frequency, because when I tried to check square wave from an inverter using this software it simply did not work.

              Can you please specify which two inverter designs are you comparing? Is it from this website??

            • Thanks Swag, i got an oscilloscope, the waveforms are different for the utility, pure and modified sine inverter. I tried tweaking the filter output and the pwm preset but the pure sine inverter I made using your bjt/ pwm stage didn’t come out as perfect as the utility power supply. Although the waveform was better than the modified inverter. Please how can I improve this. Thanks.

            • Hi Tinuke, what kind of SPWM are you seeing in the oscilloscope? How many blocks are there on each waveform and in what order? Please clarify these I may try to help!

            • There are combination of sine and sawtooth waveform( occasionally), 2 blocks in a waveform. There are different waveform with different load. Thanks so much sir.

            • Please check on the DC side, and make sure the blocks are in the SPWM format, that is widest block at the center and gradually narrowing blocks on either sides.

              Total number of blocks should not be more than 7

            • Tinuke, it number of blocks should an odd number, like 3, 5 or 7, and the widest block should be at the center, so please make sure the SPWM is configured correctly.

            • the widest block should be at the center! and preferably there should be 5 blocks as shown in the IC 741 output in the above article

        • Good day sir, from the spectrograph of this pure sine inverter I built, there are so many harmonics as compared with the bought pure sine inverter an the utility supply, please how can I reduce the harmonics, I have used different filters. Thanks Swagtagam.

          • Hi Tinuke, Can you show me the image of the spectrograph? I’ll try to analyze the reason. Upload it to any free image hosting site, and provide the link here.

            • By the way you must use an oscilloscope for analyzing the waveform, i am not sure how a spectrograph can work for analyzing inverter waveform.

    • yes it can be perhaps done, by modifying the transformer, mosfet stages in the same way as implemented in one of the relevant designs in this website.

  32. I made this circuits working perfectly 1.5kva/24v, with LC filter but when I load my washing machine at few times the output frequency which was set at 50hz jumped to 2.2khz,16khz…. For 1second To return to 50hz, why this, what can I do, I added more filters no difference. Thanks

    • one should be NPN and the other PNP….BC546 is not a PNP, so please make sure to replace it with a pnp
      by the way the shown pair is not BC556/BC547…rather they are BC547/BC557…

  33. thanks sir for your quick reply
    one more thing sir to creat the SPWM device that mean instead of using two ic556 to creat slow and fast triangular wave form i can just make use of only one ic555 and ic741 while i tap a slow trianguler wave form from the sg3525 to generate SPWM for the inverter

    • yes that’s possible, but just check and confirm whether the triangle wave from the SG3525 has a peak equal to the 555 triangle peak or not…they should be approximately equal for optimal results

  34. sir i was reading through some of your comment to ( mr faith) of how to generate SPWM under this thread you said that one can extract triangular wave form from pin 4 of sg3525 for slow triangular wave form
    and pin 6 and 2 of any ic 555 wired as a astable circiut for fast triangular wave form
    sir my question is that the diagram of ic555 being provided by you sir has a resistor port for adjusting the PWM output
    sir my guess is that as we adjust the port we increase or decrease the voltage at the transformer output or will we have to modified the ic555 circuit
    my last question is sir are we going to make use of the PWM being generated by the ic555 thanks sir

    • Abioye,
      As per my assumptions, adjusting the PWM to extreme levels may cause abnormal SPWM behavior, because too narrow or too wide PWMs may force the triangle waves to become discontinuous or without significant valleys between the triangle waves which can cause inefficient SPWMs. But yes it can be applied for controlling the output RMS voltage of the inveter. The ideal PWM should be to a 50% ON/OFF cycle for initiating a reasonably uniform triangle waves…all these will to be verified with practical trial and error method…

  35. Hi swagatam , my friend bought a standard purewave inverter, but about 6months the crt TV got burnt why the led TV is still working. I found the parameters are still 228v output voltage, frequency 50.12hz, what could make the TV got burnt.

    • Dayo, LED/LCD TVs normally incorporate a stabilized SMPS for powering the circuitry…therefore these are well protected internally and can survive upto 300V, and that may be reason why the LED TV is not yet affected, while the CRT which was not so well equipped burned due to a possible switch ON surge…

    • Good day sir, I built this inverter, but within hours of use with my CRT TV, the TV color behaves funny in that the pictures go so dark that I barely see the image then later come out so nice. Please what could be wrong sir, help out. Thanks

      • Dayo, that could be due to a loose connection, a bad solder, or a low battery…..please use a good PCB for making the inverter circuit and check the response again…also make sure the output from the inverter is below 250V

      • OK sir, but the old modified sine inverter I used for years didn’t have this issue but I wanted to try to upgrade to pure sine wave using a 555 ic and an opamp ic with your bjt stage.

        Even now when I uae the modified inverter it now have the same issue. Please help .

        • It will be difficult to understand because I don’t know anything about the modified inverter circuit and its specification. The best thing would be to monitor the waveform and voltage during the testing period…

  36. I know how to generate my spwm what am asking is that i will be needing a second opamp for my feedback and again

    Please can you give a range which the frequency of the filter will fall or can it be the same frequency as the spwm

  37. Ok that is i will be needing a second opamp, and again Please can you give a range which the frequency will fall or can it be the same frequency as the spwm. Lastly can i use the circuit for hbridge

    • for the triangle slow wave you can extract it by processing the output from pin#4 of SG3525.

      the fast triangle waves can be achieved from pin#6/2 of any standard IC 555 astable circuit

      you can use the SPWM circuit for H-bridge also

  38. Good day Mr swag., i want to thank you first for your good work, but i have few question to ask
    1. If i use spwm to modulate the signal i.e instead of using pwm i now use spwm how do i set my feedback considering that i will generate my spwm using two 555timer and one comparator.

    2. What will be the frequency of my output filter is it a high frequency filter or a low frequency filter

    • feedback can be achieved through an opamp comparator stage by configuring it with a resistive divider stage across the inverter output, and the output of the opamp fed to pin#1 of IC 3525. The resistive network should be adjusted such that whenever the output tends to go higher than the normal level, the oamp output turns high narrowing the PWM content

      the output should have a high frequency cut off filter

  39. Good day My Tutor,
    Is it possible to use a none centre tap transformer in any inverter circuit using already a center tap transformer? If real , what modification can be done?

    • Ekoe, that can be possible only if the oscillator section replaced with a full bridge IC stage, please type full bridge in the search box, you will be able to find a few concepts using this topology.

  40. Hello Swag, When you are building any Power inverter circuit , and you want to match with a transformer to obtain a maximum loading power for example a center tap, is it the voltage that you have from the output A& B of the circuit as a driver voltage let’s say from 3-9volts to the power transistors , on that you base your transformer input voltage say 7 -12volts?

    • You have to consider the average voltage which is coming to the gate or base of the power devices from the IC, and then make sure that the current of the trafo is selected as per the load wattage with respect to this voltage, that is if the required load wattage is 200 watt, and the average voltage from the IC to the mosfet gate is 6V, then the trafo must be rated at 6-0-6V and 200/6 = 33 amps for primary…and for secondary this will be proportionately = 200/220 = 0.9 amps.

  41. Hello Engineer,
    Please educate me on this very issues and ease my mind. My question is odd, and is this, Any time I am browsing through the internet and I see any educative article either in video or not, films and music. You will always see subscribe, now if I go ahead dowloadind Am I doing harm in cheating on the publisher of these articles? Or the money deducted from my internet bundle after is shared indirectly to the owner of the website. Please what is the right procedure, endure with me thanks .Because I want to correct my mistakes.

    • Hello Ekoe, subscribing and downloading is not wrong for the publisher, but frequent downloading will increase your internet bill for sure

  42. Hello Mr Swagatam happy new year,
    My tutor, am building a modified inverter with sg3524 circuit. I used 1400VA transformer from an old UPS, When I put power into the inverter the battery negative terminal get what quickly within 1 minute as if the cross section of the cable is small. Also the power transistors run very hot which cannot last for an hour .The primary input of the transformer reads 9volts a center tap, and it sounds heavily when powered. Am confused engineer, resolve my problem please thanks.

    • Happy New Year to you Ekoe,

      This can happen either due to a mismatch between between battery voltage and the transformer voltage rating, an unbalanced trafo winding or a faulty IC which may be generating incorrect oscillations or frequency. please check all this parameters using an oscilloscope or other suitable test equipment and make sure these are perfectly implemented

  43. Many thanks to you. Sir I have a problem on the buffer stage, am getting 4-5 volts on mosfets gates instead of 12v why? I have changed all the transistor still the same, I also tried other transistors(c1815 and a673) on another pcb no change. But when I isolated base of the bc557s the voltages rose to nearly12v. Where am I lost?

    • 50% less reading is fine, and is due to 50% duty cycle of the SG3525 oscillator wich is causing the meter to simulate the average 50% value of the supply level, you can confirm the same on the output pins of the iC directly…if the readings match then you can assume this to be perfectly normal.

      removing 557 removes the negative cycles from the reading, causing the meter to show only the ON time, so may be this is causing the 12V to appear on the meter

      • Thanks once again for that. If that is normal as you said then will that be good enough to drive 20NM50 on h-bridge without causing them to overheat?

        • What you are seeing on the meter is the average value of the voltage but the peak value is always 12V (or the supply level), meaning the ON time of the frequency is always producing 12V, therefore any connected mosfets will have no problems conducting optimally

          • Thanks once again. I have introduced the 555 circuit to my inverter but now the lower two bc547s are shorting the oscillations completed ie from 5.6v down to 0v. I measured the output of 555 is 11.5v but I not sure if that is PWM because I don’t have oscilloscope.
            I tried to built another circuit using other components of same marks but still.

            • your PWM IC 555’s output at pin#3 should vary from 5% to 95% of the supply voltage that’s applied at pin#4/8 of this IC in response to the PWM pot rotations.

              If this is not happening then your PWM circuit might not be working or could be having some fault…please confirm this…

          • Ok I see so what is the best position of potentiometer to achieve a fair waveform I have set it at the middle inverter working fine but I don’t know how the waveform is like because I don’t have the oscilloscope?

  44. hello sir
    i salute the great job you are doing, where else can we find free tutorials like these?
    i think you have been sent by the heavens……

    i constructed the above circuit which was drawn by Ainsworth Lynch, the 3525 did not output signal from pin 11 and 14 though it was warm meaning there was power. i looked again into the schematic and compared to the one you drew and found that pin 9 was directly connected to the ground instead to the R1 which then link pin1. after that correction there was output.

    although i am a new born to electronics ,I’m a hobbyist of electronics wiling to know better.
    My question is ……. whats the prpose of 555 and lower two transistors ,can that not short pulses from 3525 to ground?

    • Hello Francis,
      I am glad you liked my site.
      Yes it seems the drawing created by Ainsworth has a mistake, no problem readers can correct it by following the other diagram, and anyway this article is not about the SG3525 circuit, it’s primarily regarding understanding the technique of converting any square wave inverter into a sinewave.
      The IC 555 or the SWPM feed will short the waveform, but it will do it in steps which will ultimately take the shape of a sinewave at the output of the inverter therefore chopping or shorting of the actual square waveform into stepped waveform is deliberately introduced in order to acquire the intended sinewave output.

      If you have any further questions regarding any of the concepts presented in this website, you can feel free to inquire, and get them solved from me.

      • Ok I now understand the use of 555 in that circuit.one more question, how is the pwm from 555 ic incorperated to short part of the waveform at the right time to reshape square wave into stepped waveform? Is it because the two ic start at the same time or ? What if I introduce the the pwm from 555 later in the operation of 3525 ? In other word how does the two ic sync?

  45. sir swag…can you give me the part list of this pure sine wave inverter using sg3525 because other component is not clear…plss sir…

    • Hi Denmark,

      please do one thing, just copy down all the part numbers that you are able to see in the circuit diagram, and send it here, I’ll check it and verify it for you…. and if required add more info in it.

  46. Good day sir, please what can I do to frequency drift of my inverter in response to variation to battery level and load. Thanks

  47. Hello swagatam, thank u very much for helping alot in construction of this wonder inverter circuit, what i need now is to help me design a pwm generator circuit using op amp for pure sine wave output. Thanks

      • Hello sir, i have to questions to ask:
        1. what is the minimum AH battery can each of the inverter can handle: 5000w, 2000w, 1000w?
        2. What is the maximum current for charging each of the battery: 100AH, 50AH, 12AH?

        • Hello Solomon,

          the circuit can handle any battery with any rating as desired by the user.

          The mosfets and the trafo ratings will need to be matched with the battery rating appropriately.

          It is ideally 1/10th of the AH rating, divide the AH with 10…..

            • If two mosfets can handle the power then adding extra two will be a waste, it’s your wish, you can add them if you want.

              You can use a 50 AH battery for a 500w trafo , there are no restrictions as such…

  48. Thank u very much sir. Pls more questions sir. I raised an argument with my friend about N channel power MOSFETs, there are some of the MOSFETs that has a diode symbol on their body, he said that those that have the diode symbol on them are local quality product and get hot easily or even burst during operation while those that doesnt have the symbol are good and original quality, and i oppose that. Pls help me with the correct answer.
    Second question: in the second circuit containing SG3525 Ic, which type of capacitor can i use for the non polarized, is it ceramic or polypropylen type or both. help me and clear my doubt. Thanks

  49. sir pls dnt be tired with me, i wanted to gather all my questions to post, but i forgot, before i still forget, i have more questions:
    1. in choosing or selecting the MOSFETs, what must i consider, is it the volt or the amp?
    2. For knowing sake, i there any diferences or similarities between an inverter transformer and a stabiler.
    transformer in terms of winding?
    3. Can i use a stabiler transfor(5kva stabilizer transformer) to connect my inverter circuit with?
    4. What is the relationship between MOSFETs and transformer in terms of power capacity. Pls help, thanks.

    • Hi solomon, here are the answers:
      1) you must primarily check the Drain-Source voltage and the continuous Drain current ratings for mosfets
      2) All transformers work with the same principles so there’s no difference as far as functioning is concerned, only the V and I ratings may be different…
      3) You can if the winding specs are compatible…
      4) mosfets are just switches, therefore their current and voltage rating must be adequately rated to handle the trafo wattage…preferably the rating of the mosfet should be at least 1.5 times higher than the trafo max wattage.

  50. Hello sir, thanks for the circuit, i appreciate and so grateful. I have something to ask whether it can work, can i configure those MOSFETS in pairs? (meaning each side two-two)

  51. Good day sir, I made a 36v inverter but I have issues with the duty cycle, without load is 60% but with load 50%. I have tried LC filter but no avail, please assist.

  52. hello sir.. thanks for updating our ideas on electronic.. please sir I need an Automatic change over circuit that will automatically switch over my inverter to power source in my room when light is been restore.. thanks

  53. Hello sir, pls i have few questions to ask:
    1. I want to add power transistors (2N3055) to this circuit when completed with the SG3525 circuit, and i want to use the arrengement and the pin connection like the circuit of 200VA square wave inverter u posted, i want to increase the wattage of the circuit using the transistor, pls help me to configure the pin connections where to connect them.
    2. Can i use the AC mains output of the inverter circuit to a 12v battery charger to charge the battery of the inverter itself? Is there any effect to the battery or to the inverter? Pls help me sir. Thanks

  54. Thanks sir, I made a pure sine wave inverter 1Kva , buy goes off after 40mins which I will need to switch on again, mosfets are cool. I troubleshoot , couldn’t get the fault. Please, what can I do . Well done sir.

    • Love, which circuit did you make? without seeing the schematic or the block diagram it can be difficult for me to judge the fault??

  55. sir can you suggest what is best in our thesis project….we want to build a power inverter for our school…in case of power outtage we have emergency electricity…we want to installed it in our electronics lab…plsss sir…we need a tested power inverter that can run the appliance at the same time …tnx sir…

  56. Please sir, if I want to do 48v inverter, will I feed 48v +dc battery in bjt stage or will I step down to 12v to feed into it. Thanks

    • Dayo, only the trafo center tap will connect with 48V source, rest everything must be isolated and connected with a 12V or 15V input

      • Sir can i ask if these project is tested…and can you give me the parts list of this project….sir i am a electronics student turning 4th year college and our thesis project is power inverter using dual motor…can you suggest sir if what inverter is the best for our project….that can run the appliance and bulb in case of power outtage or brown out in our school..we want to installed it in our electronics lab.. Thank you very much sir…godbless you

  57. Hello sir, pls i have some question that u should help me answer in the first circuit:
    1. What output waveform, it is modified sine wave or pure sine wave?
    2. what is the function of the two MOSFETs at the 12v tap of the transformer
    3. What does it mean by the resistor 10E
    4. How can i attach/connect the pins of a power transistors(2n3055) to the circuit. Pls sir help me to answer them

  58. Hello Mr Swaggart, Can a choice of a timing capacitor and resistance when calibrating an I.C for frequency let’s say 50hz.Would it influence the d.c & ac current or voltage at the outputs of the I.c circuit. Is it a factor? Please Doc.

    • Hello Ekoe, do you mean to say the duty cycle?? yes the duty cycle or the ON/OFF time of the 50Hz frequency can affect the output current and voltage….it should be set at 50% duty cycle to ensure a 100% current/voltage output

  59. Hello, I made two inverters one works at 150hz but the mosfet did not blow with an inductive load but blow at 50hz for the second inverter. Why, and what can I do

  60. Good day engineer, I made a 36v inverter(secondary trafo guage is 16swg)
    but when used to power washing machine, the machine works heavily but when used with 12v inverter, the machine works smoothly.

    • Tinuke, it’s simply beause your 36W inverter is not correctly built and it is not delivering the required amount of current to the load….you can confirm by attaching an ammeter in series with the battery and check how much current it draws, and then multiply the result with the battery voltage…that will give you the output power range of the inverter

  61. if you think everything is correct then where is the fault?? something has to be wrong somewhere…which you must find out

    you cannot troubleshoot or build a circuit without understanding the stages or without proper equipment.

    please do not make it blindly, check the stages with a meter with proper understanding, if your BC547 is ON continuously it means your 741 IC is not producing the PWMs.

  62. Please help me design a circuit for inverter voltage stabilization in reference to varying battery voltage and load variation. Thanks sir

  63. Try adding a 4.7V zener diode at the output of the IC 741…may be the IC 741 is generating a leakage voltage which is causing permanent switch ON of the BC547

  64. you must check waveform for this circuit, checking volts will not help…
    please don’t do it unless you have without proper equipment and detailed understanding.

    • how would you check the output waveform and whether it is generating PWM or not?, please tell me how will you confirm this without a scope???

  65. Hello engineer, what would happen if any power inverter built with 60hz frequency is used for electrical gadgets operating on 50hz frequency.
    And if there would not be any trouble can this application be done the other way round ?

  66. hi
    iam building an 1KVA inverter using isw20n90 mosfets. but i needed a closed loop pwm driver ic for my inverter
    can you suggest me any IC which i can get it in market.

  67. Hi Sir,
    I am designing a Bi directional Inverter for domestic application having a variable load, I should drive mosfets using a spwm IC which can support a closed loop purpose,
    The output load limit is 600 W, the mosfet used are isw20n90, the switching frequency shall be greater than 200kHz, can you please suggest me an IC for this purpose
    Thanks in advance

  68. Hi Swag,
    I want to know if adding a pull-down resistor between the outputs of SG3525 (before connecting the gate resistor) will help the switching performance of the IC.

      • Swag,
        Everything is working very fine now. At first, I used IRF250 as my power MOSFET (one for each arm of the switch).
        When I tried using 100N25 (two for each arm of the switch), the MOSFETs burns out. I have repeated this and the MOSFETs kept burning.
        Whenever I revert to using a single IRF250, the inverter works very fine.
        Can you please advise me on what to do, thank you.

        • Hi Reoc, if one type of mosfets is working and the other not working then clearly the one which is not working could be a non-compatible type for the present application…or possibly those are faulty originally…

          can you please tell me the voltage and current specifications of the bad mosfets from its datasheet, that will help us to confirm the tests.

        • Hi Swag,
          From my observations, it seems like the burning MOSFETs were not clamped firmly to the heatsink. I believed this because any of the MOSFETs clamped firmly to another heatsink works very well.
          I want to know if this can cause them to burn out.

          • Hi Reoc, that may be possible, however mosfets are positive-temperature-coefficient devices, and therefore will normally try to shut-down as its core temperature increases, so a loose clamping may result in poor efficiency, but not in the burning of the mosfets…there could be some other potential reason.

  69. Hi Swag,
    What can cause my MOSFETs to burn within 5 Seconds?
    I am using a gate resistor of 22ohm and I connected a 10k resistor between the gate and the source. Please help me out, thank you.

    • Hi Reoc, if its blowing even after connecting everything correctly, then the possible cause could be the reverse spikes from the trafo winding…try installing rectifier diodes across the cathode/anode of each mosfets and see if that helps.

    • I discovered that there was a dry joint (not properly soldered) in one leg of the SG3525.
      I have soldered it well but there is another problem, the 22ohm resistor connected to the gate burns out after a short time.
      Please can you help me by suggesting a solution to this, thank you.

      • 22 ohm is the gate resistor which should never burn because mosfet gates have a high impedance, it seems your mosfets are damaged or faulty originally.

  70. Hi Swag, I think when the frequency of the second PWM is 200Hz, it will only chop the primary wave into two. For you to chop it into four, the frequency of the second PWM must be 400Hz. I just simulated it. Please correct me if I am wrong.
    My question is, is there any advantage or disadvantage of given a feedback voltage to pin 1 of the primary PWM for voltage regulation?

    • Hi Reoc, Let me analyze it:

      50 Hz corresponds to 10 milliseconds, 200 Hz corresponds to 5 milliseconds, during each 10ms ON time of each mosfet, the PWM would chop this 10ms pulse with 5ms ON/OFF periods, which will result in 2 ON and 2 OFF pillars, that’s 2 pillars for each 50 Hz, so it seems you are right it should be 400 Hz for generating 4 ON time pillars on each of the 50 Hz cycles.

      • considering the RMS is dead fixed, the feedback becomes unnecessary, because the output would be always constant regardless of the load, unless the load exceeds the inverter’s max wattage limit, or the battery goes below the acceptable discharge limit.

  71. Hi Swag,

    Hope you are doing well. One question. What should be the frequency of SG3524/25 on its pin 11 and 14 if I require output of 50Hz. I assume it should be 100Hz because there is a switching between these pins.

    • Hi Saqib,

      it should be 50Hz according to me….50 Hz corresponds to 20ms, therefore 20ms wave pulse on each of the pinouts will allow a +/- 50Hz waveform at the output

    • OK. second inverter using SG3524 is almost ready. but I am having an issue. one of the mosfet is heating up without any load in 5 to 20 seconds. while the second one is cool. and transformer giving little noise. Can you please guide me from here. SG3524 is powered on with 8 volts using 7808 and 547/557 are powered on using 7812.

      • If the IC powered with 8V then the emitter of BC547 will also create 8V, infact only 7V which could be quite low for the mosfet, feed the IC also with 12V and check the response, and anyway an extra 7808 is simply not required, you can use the single 7812 supply for the complete circuit stage.

      • Tried it. but dont know what happened. IC is oscillating correctly. I am getting 5+ volts on pin 11 and 14. Mostfets are cool. 13.4v on center point of transformer. BUT output is zero. transformer isn’t making any noise seems not working anymore. I am trying to find out the reason. any quick suggestion?

        • use 12V motorcycle bulbs in series with the mosfet drains, if they light up then the mosfets are working otherwise they are not.

          if you BJTs in Darligton form you will get guaranteed results.

          You can try TIP122/TIP35 in Darlington combination on each channel…the results will be immediate with 100% success.

        • I dont have motorcycle bul. Any replacement. And do you have any example for whatever you have said for BJT and TIP transistors?

          • you can any 12V 2 amp bulb for the testing.

            for the Darlington, connect the base of the TIP122 with the IC output, connect its emitter with the base of TIP35, connect the collector of TIP122 with the collector of TIP35, connect the emitter of TIP35 to battery ground…the collector joint of the transistors will go to the trafo tap

          • Can I feed TIP122 base with output coming from emitters of 547 and 557 so I will require a small PCB in addition to whatever I have printed already.

            Also can you please confirm for any replacement in case of unavailability of TIP122/35. I have to go market to get them.

            Also do you think there is a way to join any two transistors to get same functionality as these TIPs?

  72. Well done sir, please I built a modified inverter of 24v(2kva) and 36v(3kva) input, both when used to carry pump 1hp draw almost the same current (20amps,dc), what could be wrong .

    • Reoc, are you referring to the fast triangle waves? you can select it as per your own comfort, it can be 4 times the slow frequency or 10 times…but higher difference will cause higher harmonics and will require more sophisticated filter for cleaning it up….but higher frequency will also enable more improved sinewave replication

  73. Sir,
    Thank you for your reply.
    From your reply, does it mean that I need a transformer of 24-0-24, if my battery bank is 48VDC?
    If your answer is yes, please explain the reason to me.
    Must the filter capacitor be that value in your diagram? What if I reduce or increase it or completely remove it?
    Also, is there any need for a feedback to pin1 of the primary sg3525 for voltage regulation?

    • Reoc, yes that’s correct, due to the PWM chopping the average battery voltage will be reduced across the trafo primary which will result in a dropped voltage at the output, to compensate this loss the primary should be also equivalently reduced to match this.

      you can read the following article for more info

      https://homemade-circuits.com/2017/07/inverter-voltage-drop-issue-how-to-solve.html

      the filter capacitor will need to experimented for achieving an optimal outcome!

      pin#1 PWM control can be eliminated or ignored if the IC 555 PWM is incorporated.

  74. Already, I have a working PWM inverter based on SG3525 that I want to upgrade to a sinewave inverter. Thank you for the knowledge shared on this web page.
    1. Can I use a second SG3525 PWM whose frequency is 200Hz, from pin 4 to power the lower side of the circuit (I mean the signal that divides the original signal into 4)?
    2. Concerning the transformer, should I use ordinary 12-0-12, 220V transformer?

    • yes that’s possible, you can use another SG3525 for generating the 200Hz PWM chopping, but the same can be done using a simple and cheap IC 555 circuit
      The inverter transformer must be rated at 6-0-6V/220V if the battery is 12V, the wattage of the trafo should be appropriately selected as per the requirement.

  75. Hello sir Swagatam, I must say that you are doing a great job in educating electronics hobbyists. Keep up the good work sir. I’d like to ask some questions sir.
    1. From the schematic above, you used a fixed resistor as Rt instead of a pot. I’d like to know why sir.
    2. Can the schematic above be upgraded to construct an inverter up to 10KVA merely by increasing the number of MOSFETs, size (power rating) of transformer and battery voltage as explained by you in the comments without any modification? If no, what is the maximum capacity that can be built from the schematic and what modifications are required to upgrade it up to 10KVA or above?
    Anticipating your response. Thank you sir.

    • Hello Godson,

      the last schematic was taken from the internet, it is not my design, I have just provided an example design which can be integrated with the first PWM controller stage. If you wish you can change the Rt with a preset, or you can even replace the entire SG3525 stage with your own SG3525 version.

      you can upgrade the above design or any inverter design to any desired level, simply by upgrading the mosfets, trafo and the battery proportionately.

      You can add as many mosfets you want in the design for upgrading its handling power.

      • Thanks so much for your prompt response sir. I sincerely appreciate it. I still need you to help me with the answers to the following questions:
        1. I’d like to use your own design, the one in “Modified Sine Wave Inverter Circuit using SG3525”, which has low battery auto-power off and automatic output voltage regulator. But in the comments, you said that the voltage regulator can be removed since voltage can be controlled with the preset in the PWM session. Please I need you to confirm that sir.
        2. As regards the upgrade of the schematic, please I need you to help me with how to calculate accurately the number of mosfets per transfo capacity per battery voltage. Say for example, for a 1KVA inverter using (IRFP150N), I can use six of the mosfets, (three on each side) with a 9-0-9V transfo (as recommended by you) and powered with a 12V battery. Is there any formula to use for the calculation? If yes, kindly help me with it and if no, I’d like to know how to get the combination correctly.
        Thanks a lot sir.

        • Thanks Godson,

          yes a voltage regulator may not be required if the PWM is correctly adjusted and remains fixed at that level. however if the voltage drops due to heavier loads then that cannot be corrected by any means…expect by enabling further upgrades to the trafo and the batt.

          number of mosfets can be simply calculated by dividing the max output wattage by the mosfet amp rating, making sure that the voltage rating is correctly selected as per the battery level.

          • Thank you very much for your response sir. But I didn’t quite understand the last sentence: “number of mosfets can be simply calculated by dividing the max output wattage by the mosfet amp rating, making sure that the voltage rating is correctly selected as per the battery level”, especially the last part of the sentence. I’d really appreciate it if you could shed more light on it, possibly with an example. Please pardon me, I’m quite new to inverter construction. Thank you sir.

            • Godson, from the datasheet find out the “continuous drain current” or Id rating. then divide the wattage which you intend to have at the inverter output with this Id value.

  76. Sir I have seen a 555 based ac inverter circuit in this circuit C L C π circuit are connected between transformer Driver (Bjt) and primary side of transformer indu used in series and its caps respect to find, can I use this cap indu cap π circuit with 3525 for accurate 50 Hz pure sine wave ??????

    • Arijit,
      the frequency input to the primary side must be a PWM based, only then your filter design will work to create a puresine, for an ordinary sg3525 design this arrangement won’t have much effect.

  77. Good morning Swagatam,
    I need a very sensible circuit for power inverter A.C. output protection which would respond to all loads.Only for short circuit due the use of economic bulbs. Secondly what can I use when testing a pure sine wave inverter if don't have oscilloscope.

    • Anthony, presently I do not have this circuit, if I find one will update it.

      only an oscilloscope can be used for testing waveform, there's no other alternative

  78. thank you,

    however 225 watts from 210 watts is not possible, you calculation may be incorrect.

    you can high efficiency inverter by using a ferrite core trafo, full bridge topology and a li-ion battrey

  79. Hi swagatam, its me again joe, I am working on a new project and i need your help cos i got stucked somewhere. I am working on a transformerless inverter. As we all know that, a transformerless inverter requires high-voltage DC to be fed into H-Bridge in the desired waveform. Fine, I have chosen EGS002 as my DC-AC SPWM driver, now before i can use it, i need to generate 250V DC or above from a 12V battery. Now, i opened up an abandoned transformerless inverter, i removed the ferrite core "color yellow" transformer inside, so as to use it to generate High Voltage DC. I choose IC 4047 as my oscillator. This small ferrite core transformer is a center-tap transformer, so, i configured my IC4047 to oscillate at 5KHz, and i used 10 Ohms resistor to the gates of my FETs, with a reverse diode (1N4148) connected in parallel with the resistor to aid the quick discharge of the gate capacitor inside the FETs, so as to improve the performance of the mosfets. At the output of the ferrite core transformer, i placed a bridge rectifier (Using 4 pieces of 5 Amps Thick diodes) with a 400V 120uF capacitor. Note that the circuit is made in a Push-Pull manner (i.e. 12v connected to the center-tap, and mosfets placed on right and left hand of the trafo).

    When i powered the circuit, it works and on my meter i saw around 270V DC. But, here is the problem

    I am using IRFP250 mosfets and the get HOT within 5 seconds of operation, i mean, really hot. The heat sink get really hot, so i quickly remove power. Please, how do i correct this problem. Thanks

    • Hi Joe, that could be happening due to mismatched frequency and turn ratio of the ferrite trafo, try increasing the frequency and see if that improves the situation.

    • Sir, i have done as you said, i increased the frequency from 5kHz to 60kHz, i can see improvement in the performance of the circuit. The ferrite trafo did not buzz again and the temperature is normal, the mosfets too, they still get hot, but not like before. there is an improvement. they get hot within 30 – 45 seconds of operation. unlike before which gets hot immediately. Is 60kHz enough? or i should still increase it??

      Also, i noticed IC4047 that i am using is not too good for high frequency oscillation, i checked on my scope, the wave form is bad, the higher the frequency, the uglier the wave form, i noticed that after 10kHz, the wave form is no longer square wave, it turns to an ugly triangle wave on my scope. I think this wave form can damage a mosfet quickly because it is not a pure square wave. I think i will need to change my oscillator to 3524 or i should use an op-amp for oscillation. Please i need your advice…

    • Joe, 60kHz is Ok, I have see some inverters even using upto 100kHz, so that's fine….and the voltage also plays an important, you can try varying the voltage slightly also, which will give you an idea regarding the correct proportion and relationship between frequency, voltage and turns, once you get the right match you can alter the parameters with different proportions as per your specifications. for the mosfets try using a buffer stage as explained n the above article, or if you want to avoid this, you can add reverse diodes parallel with the gate resistors which will help the mosfets capacitance to discharge quickly and reduce malfunctioning chances…make sure the gate resistors are not above 20 ohms

    • I have 10 Ohms to the gates of the FETs and also i have reverse diode parallel to the 10 ohms resistor. I have introduced the buffer stage like you suggested and changed the fixed resistor of 4047 to a 10K POT so that i can vary the frequency. I tested the circuit and the result was amazing. First, i vary the 10K POT so that i get constant 20kHz and i test, the result was awesome, FETs worked upto 2mins before getting warm (Not HOT), i think this is normal, also, there is no huming sound, everything is cool. I tried to vary the POT again, and i noticed that, anything below 20kHz, the traffo will produce a humming sound and FETs will get HOT, but 20kHz, working condition is normal. But i am faced with a new problem. I dont really know if it is a problem. The output voltage on my multimeter reads 550V DC (on no load). I am not sure if i add a load, maybe it will go down. I have a bridge rectifier and 450V/150uF cap at the output. I noticed that the voltage is even above the voltage of my capacitor. I examined the temperature of the capacitor, and its normal, not hot, not warm. I am confused, i don't know if i can proceed by making use of this 550V DC and feed into h-bridge. Please advice me.

    • Joe, a meter might produce confusing results while measuring high frequencies from an inductive system. if you check the peak and the RMS with a scope you will surely find it to be correct and as per the expectations.

      and yes it will become normal as soon as a load is connected

    • Sir, you said "if you check the peak and the RMS with a scope you will surely find it to be correct and as per the expectations" how do i do this? The voltage (550V) is too high for my scope and will damage my scope. In the user manual of my scope, it says maximum voltage of 50V AC or DC. How do i test it on scope??

    • Joe, 550V is not the correct reading from the meter, your trafo is rated to generate 330V from a 12V input so 550V is not possible.. that is what we want to confirm from the scope. you am verify the same by connecting a small load of 10 watt….

      you can use a small 0-12V/220V trafo and step down the output of your inverter, and then measure the 12V side with your scope, this will you to get the proportionate value, which can be then used for calculating the peak and RMS of the inverter through simple cross multiplication

    • Sir, i have not completed the inverter, I am still working on the DC-DC converter, after getting it right, i'll do the DC-AC conversion. That was why i asked that, with the information i have now, can i proceed by using this voltage for my h-bridge dc-ac? Should i proceed?

    • Sir, How do i confirm 330V DC?

      You said:
      550V is not the correct reading from the meter, your trafo is rated to generate 330V from a 12V input so 550V is not possible.. that is what we want to confirm from the scope.

      YES, I agree, but my scope cannot measure any voltage above 50V, otherwise, it will explode.

      You said:
      you can verify the same by connecting a small load of 10 watt….

      I don't have any electronic device that run on high volt DC, max DC electronic i have is 12V DC and also, the AC load i have is 50-60Hz and cannot run on such high frequency i'm operating. So, i cannot get a load to test.

      You said:
      a meter might produce confusing results while measuring high frequencies from an inductive system

      Yes! i totally agree with you. But how do i get the "ORIGINAL" voltage readings?

      What i did, i placed one multimeter at the output of the ferrite before the bridge rectifier to measure the AC voltage and another multimeter after the bridge rectifier to measure the DC voltage. The first meter measuring the AC fluctuates between 170V AC – 240V AC, while the second meter measuring the DC stays constant at 600V DC. The capacitor after my rectifier is 450V/150uF. Now, my conclusion is:

      AC voltage reading fluctuates because the frequency is too high for the meter to handle
      DC voltage is showing such high voltage because, no load is connected and also, the capacitor might also store and store and store more energy that is not been utilized.

      So, my assumption is, i think the circuit is safe to operate (just a guess), since the AC voltage is between the safe voltage (even though its not 100% true).

      Sir, that is my assumption, please correct me if i am wrong.

    • Joe, you can connect a 10 watt incandescent bulb as the load and then check the parallel output with the meter, I am sure you would have a small 220V/10watt or 25 watt incandescent bulb with you or you can procure it from the market.

      the bulb will operate on both AC or DC without issues

      • Sir, i have just ordered two incandescent bulbs. Those bulbs are not available in my country, so i have to order it on xxxxxxxx and ship to my country, to it took a month for it to arrive here. Now i have those bulbs, and i test it on my circuit. Without the bulb, like i said earlier, my multimeter reads 600V DC steady and mosfet gets hot in less than two minutes. Now i got 220V-240V 40W incandescent bulbs and i connected one to the output of the DC, and power the circuit, the bulb came on fully and i got 260V DC steady on my multimeter. The circuit operation got better with load connected. Mosfets only get warm and not hot, everything is cool and i am very happy. Now, i want to perform another test, to be sure i am not getting too many voltage drop. I connected the second bulb to the output, now, i have two bulbs at the output with 40W each, now i have 220V and 80W load, and i power the circuit. The two bulbs came on FULLY, and i still have around 245V DC on my multimeter. I was very happy and dancing… I want to double the ferrite core traffo so that i can have more energy, cos the ferrite core traffo i have can only give me around 500W max, so if i double it, i can get 1000Watt. I am very happy….

        • That’s great achievement Joshua, congrats on that.

          yes you can try upgrading the winding by using a bifilar coil and by increasing number of strands in this bifilar winding, this will help you to achieve more power at the output, but make sure that the battery is also appropriately upgraded, along with the mosfets.

    • better to confirm first and then proceed with the next stages…you can do it in the above method, or using the step down trafo method.

  80. hello sir thanks alot yesterday i ran the first on my inverter that i have been making. the bulb was lighting but the output voltage was less than i expected i want it at 240volts.i tested it with a 9-0-9 transformer using a 12v/7Ah battery. so what could be missing. thanks

    • Hello olupot, if the load wattage is more than the transformer wattage and its supply wattage then the output voltage will drop, please go through all the previous comments to learn the exact details….

  81. Hello Swagatam, Sorry for my mistake I thought you have the previous message still.The pin#2 is connected to pin#6.Pin#3 of ne555 output is connecting to pin#3 of second I.c Sn7474 thanks. What about the 4047 circuit please sorry for the inconvenience I am causing to your blog am a starter in all.

    • Hello Anthony, OK no problem, I only wanted to suggest that the 7474 IC is not required, it is unnecessarily making the circuit complex, you can get 5kva with any oscillator IC, such as IC 555 or IC 4047 or SG3525.

      If you are interested to use the 4047 concept suggested by me earlier then you can definitely go ahead with it, it's perhaps the easiest pure sine wave wave inverter circuit you can get anywhere.

      but please be cautioned that if your are a newcomer then you must first make an effort to understand all the associated theories thoroughly, otherwise success can be difficult to achieve.

  82. Dear Swagatam, Therefore please send me your e-mail so that I can post the diagrams. Am finding it difficult pasting through your comments block and if any direction as to how to go about it,help me.I use smart phone to do all my operation I don't go to cyber café.

  83. Dear Swagatam, I did send the circuit diagram through your email about the inverter circuit I brought to yourblog for clarification (NE555&SN7474n system).You did request. And again another one about CD4047 schematic diagram. So I wish to know if you have got the circuits. GOD bless you.

    • Dear Anthony, I did not find any email in my email ID, and by the way I don't seem to have any circuit using those two ICs mentioned by you at the moment, sorry about that.

    • put 220V AC from input 220V side and check the 12V side with meter (AC)

      if it shows 12V with load (12V bulb) then your is OK

      ….connect 220V with a fuse in series and and take all the due precautions

    • it means your transformer is good, the 600V reading in your meter is wrong, connect a 0.22uF/400V cap across the output of the trafo and check again, this might bring it down to 310V

    • Hello sir,it's good to hear, but why transformer is showing suddenly such a behaviour even with both versions of inverter and how multimeter could show wrong if it's showing true reading with mains supply but 500v to 600v with 12-0-12 10A transformer and 5amp transformer is damaged fully.
      I was using 5Amp with square wave inverter since one year and suddenly.

    • It's because mains AC is clean with no harmonics, whereas the AC from your square wave inverter may be accompanied with many disturbances and harmonics, causing a false reading on the meter, did you connect 0.22uF/400V capacitor at the output as I had advised you??

      Your technician is not correct, transfomer are manufactured as per the frequency, not on the basis of square wave or sinewave…ask him to provide the technical reason why a sinewave trafo must be different from square wave??

    • Hi sir, I have tried 2.2uf 400v and 1.2 uf 400v capacitor as I was not having 0.22uf 400v as a result the battery terminal was giving spark but without capacitor the result was same 600v(with square wave only upper circuit) And as per your last comment statement"" It's because mains AC is clean with no harmonics, whereas the AC from your square wave inverter may be accompanied with many disturbances and harmonics, causing a false reading on the meter" I want to say that 1 year ago when I made only the square wave inverter from other site I had same multimeter and it showed 230v reading so why now new one will show false reading, I think there might be problems with transformer winding, as some days ago I told you that I had added mosfets in parallel which was 'not' necessary and both transformer made crispy sound so I think problems started from that time and now I prefer to arrange for a new transformer. I am using 555pwm, Now do favour suggest me a new transformer specs so that may fit according to the circuitry best with all measures.

    • Not getting things right might be very frustrating and can make someone to cry. I could remember myself in this same kind of situation months ago, but with determination, i was able to solve the problem. The major point of all this issue is UNDERSTANDING… When you understand the circuit, you'll have no problem.

      From this post, i think you're having problem with:
      1. Voltage drop
      2. Over-voltage at trafo output
      3. Bad/damaged trafo

      Let us look into the issue one after the order.

      1. Voltage drop: This occur in 3 different ways. (a) If you use low rated transformer (b) If you use low amps battery (c) When your PWM is not well calculated. If these 3 are taken care of, then you should not have problem of voltage drop

      2. Over-voltage: You need to understand that, a transformer is meant to step-up or step-down voltage. Thats all. Therefore, if you are getting high-voltage at the output of the trafo, then you need to check your input voltage. This is because, the output voltage will always correspond to the input voltage according to the number of windings. If you have a 12-0-12/220 transformer, if you feed in 12v, then you're rest assured that output is going to be 220v, and if you feed in 24v, then you should be expecting 440v at the output. So, if you're getting unwanted voltage at the output, then check the input voltage.

      3. Bad/damaged transformer: I want to tell you that, a transformer cannot damage. A transformer is made up of coil and silicon sheet, thats it. There is no electronics that can get damaged inside a transformer. Even if the transformer over-heat and melt, it still keeps working until there is a mis-contact in the coil of the trafo.

      In summary, to solve over-voltage problem,
      1. Construct a simple square wave inverter using either 4047 or 3524 IC and use your trafo with it and measure the output voltage. DO NOT USE ANY CAPACITOR AS FILTER AT THIS STAGE.

      2. If your output voltage is correct, then it means you need to do more precise calculations on your PWM circuit stage.

      3. If your output voltage is NOT correct, then it means you need to check if your battery is fully charged, and if you are getting the correct voltage at the input of the trafo. Also make sure that you are using a THICK wire that can handle sufficient amps for the trafo and the MOSFETs.

      After following these steps correctly, you should be able to solve your problem.

    • Also, concerning your engineer saying square wave inverter transformers are different from sine wave inverter transformers, i think that is wrong. Transformers are transformers, it is only winded in different ways depending on the need. Most pure sine wave inverters uses the Full Bridge (H-Bridge) Mosfet topology. So, the kind of transformer for H-Bridge has two input terminal, which means, there is no center tap. But the ones we do here, including the one i did for myself, i used a center-tap trafo because i am NOT using H-Bridge topology. So, transformers are not different. they are all the same.

  84. OK sir,(1)I understood you mean to say the 600v output without using pwm is not transformer's fault and it is normal.(2)I need to regulate it using 741 ic. And with pwm ic 741 regulator is not needed. Is it all that you want to say? But earlier this was not happening.
    Thanks

    • 600V is not OK, it should be 310V but previously it was showing lower reading so it seems your meter could be wrong, or the transformer could be originally of bad quality and might have got shorted because of some low quality winding….but normally a transformer can never get damaged without getting burned

  85. Hi sir, ok I will follow your advice now tell me what is solution of my problems instead of buying new transformer what can I do if get 400v output should I use voltage correction circuit and are you sure voltage correction with that circuit will be best solution and not cause any problems. Please reply till night so that I could go to buy ic 741 from market.

    • Hi Abhishek, all my solutions were the best solutions but you did not follow them so far…that's the reason you are still struggling with a simple inverter circuit.

      Please note that I may not repeat what I have already explained you many times.

      to get 400V you must use a lower voltage rated trafo than the battery voltage, but since you were not ready to buy a new trafo I suggested you to buy another battery and connect it in series with the existing battery, you did not do that, so please do whatever you may feel may correct, or you can read the links which I have already suggested you previously and advised you to first learn the concepts thoroughly and then move ahead….

    • PLEASE READ FULL…
      hi sir , Currently I am not having voltage drop issue .please,And i dont want
      400v(why i will wish for 400v i am already getting 600v) .From yesterday I am saying you that suddenly transformer started giving 500 to 600v.i have checked both of my inverters with same transformer and also with 5amp transformer result is almost same .AND EVEN WITHOUT PWM ALSO THIS IS HAPPENING.
      I THINK YOU WERE UNABLE TO UNDERSTAND MY APPEAL.PLEASE READ FULL .
      I DONT HAVE VOLTAGE DROP PROBLEM. PLEASE TELL WETHER THE TRANSFORMER IS FAULTY OR IT CAN BE CORRECTED THROUGH VOLTAGE CORRECTION CIRCUIT.my whatsap number is 8826825108.

    • Hello Abhishek,

      I have already explained you many times, and this is the last time I would be explaining, please write it down on a paper:

      1) adjust the PWM to reduce the output voltage (RMS) to 240V, if PWM is not use then you can use the 741 IC regulator circuit to drop it.

      2) if PWM is used make sure to connect a 0.22uF/400V or 0.33uF/400V or any such suitable capacitor to bring down the output to 240V even without load.

      3) with PWM connected, if you see output dropping to 170V or lower then that could be due to low trafo current spec.

      to correct the above voltage drop issue you can read the following article thoroughly and act accordingly

      https://homemade-circuits.com/2017/07/inverter-voltage-drop-issue-how-to-solve.html

    • correction 3) point:

      with PWM connected, if you see output dropping to 170V or lower UNDER LOAD then that could be due to low trafo current spec.

  86. Hello sir, I have checked multimeter with mains and it's showing 220v and 217v which is fine, are you sure the reason you mentioned are only to get transformer damaged and not the other reason ?Both The transformer never heated
    And both inverters can't be false I'm feeling right now tired man, please read previous comments for more problems details this is first time in life I'm facing so much of problem in making something. Please help and don't get angry.

    • Hi Abhishek, I am sure of that, before a transformer gets damaged it will emit smoke or at least emit a burning smell…even burnt trafos keep working until the winding is completely shorted…if you proceed with proper understanding and follow my instructions then I will surely keep helping otherwise I may lose interest….

      if you are tired then you must quit electronics and stop pursuing electronics….

  87. Hi Abhishek, a transformer will get damaged only if it gets too hot and burns, there's no other way a transformer can get damaged…I think your meter is faulty, and malfunctioning

  88. Hello Mr Swagatam, I am at my wit end just the fact that I am not a skill type in electronic.Your circuit sg3525 pure sine wave, am still unable to get my 50hz frequency having done all I could with my little Automobile electric knowledge. Dear designer, inventor and public mentor, I wish to bring on your table an old power inverter circuit for your clarification, this I built several time. But it has very small output, since I began browsing through internet it has been my wish to build something more sophisticated.
    My circuit consists 3 integrated circuit. A regulator 7805 battery power source feeding NE555.And output pin #3 of ne555 connect output pin #3 of the third I.c SN7474.And from pin #2&6 and pin#5 of sn7474 is 2(22k ohms) one connected to earth and through a transistor 2N2222A through 2(820 ohms) to second transistor BD136 and finally through a 33 ohms 5 watts and 100 ohms to 2 power transistors 2N3055 to a transformer input. Please, how do I increase this to 1000 watts output and a pure sine wave? Please help I know you are not waery of our long bothering questions. My dear to you my engineer.

    • Hello Anthony, since I cannot see the schematic design of your inverter, it will be difficult for me to judge its internal functions and other related parameters, however power output of any inverter can be quite simply increased by adding more number of power devices in parallel at the output stage, ideally using mosfets, and along with this the transformer and the battery must also be proportionately upgraded to enable the power boost.

      in your case it seems 2N3055 are used, which I am afraid doesn't look be an appropriate candidate for enhancing power upto 1kva even if more number were added in parallel.

      you must select a mosfet based design for implementing the suggested upgrade, or replace the 2n3055 with mosfets, so that these can be added in parallel for achieving the intended output level, not forgetting the trafo and battery specs

  89. MR. Joe Adeoye!you save my day! i am now totally understand why too much voltage drop when connected any pwm method to make the waveform similar to sinewave. now all i need to do is use OP-AMP as SPWM and use 6-0-6 transformer.

    MASTER SWAGATAM! can i use ic556 to generate both slow and fast triangle-wave?

    • Thanks Dracir, yes you can use a single IC 556 configuration and you can collect the two frequencies from across the two respective timing capacitors.

      However, the type of PWM is not the culprit, it's the duty cycle adjustment that affects the output, so you

      must understand how the PWM functions and how it must be optimized to get the correct

      results from it.

      without PWM the duty cycle is 50%, therefore if you multiply the battery 12V with this 50%

      you get 6V, multiply this 6 with the current consumption, say for example 10 amps (for a

      10amp/0-12V trafo), you get 60 watt as the answer, for both the halves this becomes 60 + 60 = 120 watts, that's exactly what your rafo is rated, therefore you are able to get full output.

      suppose you are using a PWM 50% duty cycle, and you apply it to the gates of the mosfets, this will cut the already present 50% duty cycle further down to 25%, therefore your output will become 60 watts instead of 120 watts.

      Therefore it's not the type of PWM that matters rather it's how you optimize it makes the difference.

    • Hi Drahcir, in one of your recent comments you asked whether an SPWM would overheat the mosfets or not, the answer is no, it won't if you use the BJT buffer stage as indicated in the above article, and if you keep the PWM frequency low, meaning use just 3 to 4 pillars for the SPWM , this will keep the harmonics within limits and prevent the mosfets from getting hot.

  90. so why theres no voltage drop when i disconnect the pwm to chop the waveform? i will try to measure the ampere next time i will update you soon, and i try to change the load with 40w incandescent bulb. maybe my analog multitester confuse on monitoring the current voltages.

    • it's because chopping is cutting out the sections from the original square wave leading to reduction in current… this has to be compensated by using higher current winding at the primary side so that the winding can absorb optimal current from the high sections of the chopped waveform.

    • Also, do not use IC741 OP-amp because it requires positive and negative voltage to power it. You can use LM324 or 358 which can be powered using a single source

    • Hi Joe, I accidentally deleted your previous comment, but fortunately I had the copy saved in my email, so I am copy pasting it below for benefiting the other readers:

    • Advise from Mr. Joe

      Good day drahcir, I have been in your shoes before suffering from voltage drop problem after introducing PWM to the square wave from 3524 IC. It took me weeks for me to be able to figure out and resolve the problem. The problem i had then is that, using a normal square wave, after connecting load, the voltage still remains at 220v which is pretty good. But when PWM is introduced, whenever i connect load of 60Watt, the voltage drop by 50% i.e. from 220v to around 110v. Taking time to understand what is going on helped me to resolve this problem. First thing you need to understand is how the PWM works, when pwm is not introduced to your square wave, you have your FET turned on for 20ms and off for 20ms (if working with 50Hz) which in turns gives you the desired output. Now, when pwm is introduced, like for example, using 200Hz pwm which divides your square wave into 4 segment, you notice that the ON and OFF time has been reduced by 50% i.e. dividing 50Hz into 4 pulses, you have 2.5ms ON and 2.5ms OFF for 4 times, adding 2.5ms * 4 gives you 10ms ON and 10ms OFF, which originally was 20ms, which will cause your output voltage to drop by 50%. This is why it is always recommended to use a 6-0-6 traffo for 12v power supply, or 12-0-12 traffo for 24v power supply which will help you get your full output voltage.

      Now, concerning the voltage drop, from my experience, the filter i was using is causing the problem. Normally, after applying PWM, you need some filter at the output of the traffo in order to filter out harmonics, if no filter is used, you'll get some funny readings from your scope and endanger loads connected to traffo output. In my case, i was using 1uf/400V capacitor as filter. After adjusting the pwm POT, i got a clean sine wave from my scope at desired voltage but when i connect load of 60W soldering iron, voltage drops to 120V. The problem there was that, the filter i used was deceiving me, i.e. giving me wrong voltage readings on my multimeter. After setting the PWM POT and getting a clean sine wave, i removed the filter and check the voltage on my multimeter and i discovered that it was around 190V, and when i add the filter again, it jumps up to 240V which was a *FAKE voltage.

      So, the thing is, i wasn't really getting the voltage i thought i was getting as output voltage and which is why the voltage dropped at high rate, because, powering a 220V load with 190V source, leads to insufficient voltage and in other to complement the voltage, it will draw huge amount of current which will also reduce the voltage the more.

      I have tried several PWM with no success, i am ALWAYS faced with this same challenge.

      One day, i came across another PWM circuit on this blog which saved my life. If you scroll up, you will see another PWM circuit, using Operational Amplifier (OPAMP), to generate SPWM, all you need to do is know how to generate a triangle wave which is quite simple, generate a fast and slow triangle wave and feed them to the input of an Op-amp, and it will give you some sort of SPWM which you can use. Note that the *slow triangle wave form must be 2 times your original frequency e.g. 50Hz for 100Hz triangle wave. And the *fast triangle wave shouldn't be less than 2KHz, otherwise, your output sine wave won't be *pure. As for me, i used IC 4047 and i used the PIN 13 to generate the triangle wave for the *slow wave fed into op-amp. This gives me 100% accuracy on the TIMING.

      So, to summarize the whole story:
      1. Check your output voltage when you remove your output filter
      2. Connect a little load (like a soldering iron) without filter and read the voltage again
      3. Connect your filter and read the voltage
      4. With filter connected, connect your load and measure the output voltage again.

      As for me, the SPWM circuit saved my life and working pretty fine using 2.2uf/400V cap as filter.

      WARNING: Do NOT connect any surfisticated electronics as load. Always use something like a soldering iron as load during test.

  91. [URL=s1077.photobucket.com/user/drahcir26123/media/testing_zpsvx2lii0a.png.html][IMG]i1077.photobucket.com/albums/w475/drahcir26123/testing_zpsvx2lii0a.png[/IMG][/URL]
    Master if i slow down the pwm to 300hz the waveform chopped into 4 times, and the voltage drop form 220vac to 140vac with the load of 40watts soldering iron. i think if we use this pwm method on h-bridge orientation this will reduce the quality vs efficiency.

    • Hello, the voltage drop may happen due to the following reasons:

      incorrect PWM duty cycle
      insufficient transformer, battery current output.
      you can correct the issue by connecting an ammeter in series with the battery, and then adjust the duty cycle of the PWM until the optimal current is reached and the voltage is raised upto the desired limit.

      basically insufficient current from battery or insufficient trafo saturation is main factor that leads to voltage drop

    • pwm has nothing to do with efficiency..we are using PWM here just to "soften" the square wave DC output in terms of correctly regulated RMS value, so that it can reach close to the sine RMS value

  92. I build this circuit with difficulties,and I ended up getting 225volts but output frequency was 150hz and fluctuating down continually not stable. My Major problem was Ne555 p.w.m circuit finding the 200hz.I finally had by try and error way.So Mr Swagatam, please help me find it easily by giving me the exact values of the two capacitors in pin5,pin 2&6, of ne555 or help solve the problem. Operation sound rough.thanks God your blog.

    • you can build any SG3525 circuit, and integrate it with the PWM, it is not necessary to build the one which is shown in the 4rth diagram fro top.

      200Hz is also not a mandatory figure, it can be 300 Hz or 400Hz also, 200Hz was chosen to keep the harmonics at minimum.

      Pin#5 capacitor is always 10nF, pin#6/2 capacitors can also any arbitrarily selected value, such as 1uF/25V…the other values can be adjusted by using the following software (second option on the page)

      https://homemade-circuits.com/p/ic-555-calculator.html

      the 150Hz reading is incorrectly shown by your meter, it's probably the PWM frequency which is being caught by the meter, using an oscilloscope to check the exact frequencies.

  93. hell sir thanks for sharing your knowledge with us…..i have made this circuit but i didn't get any output please suggest me what can be done??

    • Hello Ravindra, it would be difficult to troubleshoot your circuit because I cannot see what mistake you might have made in your.

      I would suggest you to first learn all the basics and then build a simple SG3525 inverter, after that you can go for the PWM integration as instructed in the above article.

  94. Sir i have an idea in my mind. if i increase the dead time more and more, Is this decrease the pulse width.?

  95. Thanks a million Sir!
    it's really helpfull but i have still confusion. i need 40% duty cycle from sg3525 but i get maximum 49% duty cycle. i have my own design of smps dc dc converter i-e 12vdc to 310vdc using etd40 ferrite core tranformer. for which i need 40% duty cycle. i am tried on searching but fail. please sir help me how can i get my goal. please

  96. Thanks for the wonderful post sir, i have made 3524 inverter years ago and i'm using it, but it is a square wave inverter. I think it's time to upgrade it to a sine wave. Sir, i have plenty questions to ask concerning the PWM. I don't want to use IC555 for generating PWM, i would prefer to use the SWPM opamp method using IC741. From your article, you told us that, if we feed two traiangle wave into pin 2 and 3 of the IC741 which one's frequency needs to be faster than the other. Now, my question goes thus:

    1. The triangle wave, the Hi and Lo state, is it +12v and 0v or +12v and -12v (assuming i'm using a 12v battery)?

    2. Please, can you help me with circuit diagram how to generate triangle wave, i only know how to use IC555 to generate saw-tooth wave, but i have no idea how to generate perfect triangle wave. Please help?

    3. What is the ratio of the frequency of "FAST TRIANGLE WAVE" to the "SLOW TRIANGLE WAVE"? is it ratio 1:2 (example: fast=200Hz while show=100Hz)

    I joyfully await your response sir. 🙂

    • Thanks Joe, I am glad you liked it!

      Here are the answers:

      1) they just need to be +12V, and 0V

      2) If you search online regarding how to generates true triangle wave, you might surely get many related options, you can give one of them a try and check, otherwise IC 555 can be also used in the astable mode (a couple of them), the saw-tooth won't cause any problems, it will still work as good as a triangle wave.

      3) the ratio could be 1:6, this will give you six pillars for each SPWM waveform.

    • Sir, I am working on this PWM, first, I want to generate a saw-tooth wave using 555 timer, I joined pin 2,6,7 together and connected to V- with 1uF cap. The pin 2,6,7 is also connected to collector of Bc557 whose emitter is connected to V+ via 2.2k resistor and the base is connected to reverse voltage coming from 2v7 zener diode and grounded with 470 ohm resistor. Now, I placed the probe of my scope on the pin 2,6,7 which are connected, I got a saw-tooth wave as expected, but the problem is that, the bottom of the saw-tooth wave is not getting down to zero volt, I powered the circuit with 12v but the saw-tooth wave is between 8v and 3v, it is not getting down to zero volt. Can I feed this into an op amp? Will it work? And how can I make it come down to zero volt?

      Thank you sir.

    • Hahaha haha…. Worked Like charm.. You're a genius. The 555 IC in your diagram is wired in monostable mode which is triggered by pin 13 of 4047 IC, so, I used a separate 555 IC to trigger it, and it worked…. Clean saw-tooth wave on my scope. Let me continue with my work… ? ?

  97. sorry, you mentioned 23 amps for the battery…so it needs to be multiplied by the battery voltage and not 236….

    so your inverter might be OK, it's the battery which needs to be upgraded with higher AH.

  98. OK, I think you answered your question yourself….at 23amps the inverter needs to be above 5kva, while your inverter is rated to handle just 2kva….you can try connecting another battery in parallel, together they must be able to satisfy the momentary 6000 watts by the freezer.

  99. Hi, it's 100 Ampere, and your battery will be flat within 15 minutes and almost permanently damaged if it's a lead acid type.

    the rule is drawing current at 1/10th of the battery AH…this will ensure maximum good health and long life for the battery…

  100. Hello, did you check the output voltage of the inverter while your freezer is connected? if not please check it and also check the current by connecting an ammeter in series with the battery positive….and let us know the results.

  101. hi Swagatam! greetings!! I felt very glad to read your blog out here and the manner in which you responded to various queries/ clarifications raised by electronics hobbyists/ enthusiasts. I am also curious to know whether this inverter can be configured to obtain pure sine wave at 400 Hz? Why I am asking is because I am associated with Aircraft systems, and as you know they work with 115V, 400 Hz AC. Thanks. Arvind K (Bangalore)

    • Thank you Arvind, I appreciate your thoughts very much!

      yes the above circuit could be also run with a 400Hz frequency simply by modifying the relevant R/C parts associated with the IC

      However I am not sure what kind of core would suit for the transformer at 400Hz frequency, this you may have to confirm this with an expert transformer designer

    • Hi arvind, you can change any one of them or both, it may not be relevant to performance issues, the product of the two parameters basically become responsible for the frequency change only

  102. Thank you Mr. Swagatam and I appreciate your great work and efforts. I need to clarify more about the value of resistors which feed the MOSFETS. As per the given diagram, it's 10E. Can you clarify more about it please as it's not really clear enough.

    Thank you.

    • You are welcome Mohammed, the values are 10 ohm each, please click on the diagram to enlarge it and view the details clearly.

      10E refers to 10 Ohm

  103. Hi swagatam sir, can I give above circuit input from astable multivibrator circuit, if I do it, what wave form will I get as output, I'm not familiar to use ICs.

    • Hi Abhishek, the frequency input to the transistor stage can be from any suitable source, you will always get a sine wave at the output, so you can replace the SG3525 with an astable of your choice and still get a sine wave

  104. The circuit seems working but how come you did a voltage control .I explain if the no load output find yourself a 260 volts I also have more 'but that tends to fall with the load, but if you have a control of output voltage always you have a stable voltage

  105. Hi Sir,
    Can you suggest me design for 24 volt 1220 watt, 2 kW and 5 kW Solar Inverter design please… Also what will be the basic design change if wattage increases like 1.2 KW, 2KW & 5 KW…

    Thanks,
    Ram

  106. Please Sir, may I know if I can get 80khz 6kVAC Pure or Modified sine wave output from this Circuit?

    I need the high voltage to to drive 12 500g serially connected coils of 180ohms each.

    • sorry please ignore the previous answer, It was in response to an earlier request regarding a full-bridge SG3535 circuit….

      as for your question please send it again to my email I'll try to check it out and solve it.

  107. Hello Swagatam thanks for the respond on my comment. I want you to know i substitute that 555ic and 2NPN JBT with SG3524 by using 2 internal transistors of SG3524 i connect them common emitter configuration and i generate 200hz, it work OK and i connect the out put to that gate driver(npn,pnp/npn,pnp) and i generate 50hz using SG3525 finally i get this sample of wave form. i sent it to your e-mal thanks

  108. pls sir, any simple circuit to use 555ic to generate slow and fast triangle waves. i got a circuit online that produces square wave and triangle wave using one 555ic at 200hz.

    • Atinuke, all IC 555 astable will give you triangle waves across their capacitor…the frequency will depend on the capacitor value and the associated resistor value.

  109. Hi Swagatam i tried this circuit and i get the out put wave form the same with the one that you design in fist diagram, i tried my best to filter it but is denied it still square wave. so can i do. thanks

    • Hi Salman, that cannot happen, I think your PWM circuit is not working.

      please check the waveform at the base of the NPN/PNP BJTs and let me know..

  110. hi engineer, how can i replace d pot with a fixed resistor and do d calculation of d right value because the pot needs to be adjust and readjust atimes. also most of d factory made inverters have no pot. thanks.

    • It does not include an automatic correction but according to me it's not required since the PWM is supposed to take care of the output voltage and ensure a fixed 220V or 120V… unless the load is incompatible and draws abnormal amount of current.

  111. Hi Mr swagatam, it's been a while, I really value and appreciate your response / effort just to make someone like me to be able to do something on my own.

    I've completed the design but I need oscilloscope to check the wave form in which I don't have presently.

    Is there any other device I can use to check apart from oscilloscope?

    • Hi Baasit, you can use your PC as an oscilloscope and use to confirm the waveform….download the free version of Goldwave software, and then you can use it with your PC.

      for more info Google "how to use PC as oscilloscope using goldwave"