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SG3525 Pure Sinewave Inverter

Last Updated on by 460 Comments

In this post we learn how to make a SG3525 pure sinewave inverter circuit using a straightforward PWM integration.

Using SG3525 for the Basic Modified Squarewave Version

We know that the IC SG3525 is designed to produce a modified sine wave output when used in an inverter topology, and 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 Takes Place

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.

 

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:

 

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:

 

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:

 

 

 

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:

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

Courtesy: Ainsworth Lynch

 

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Comments

  1. 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.

    Reply

    • Love, did you calculate the parameters perfectly while designing the transformers? If you do it by trial and error then that won’t allow you to understand anything regarding its working principle. By the way 12 and 18 SWG ratio does not look OK, neither does does 12.5 and 16 SWG ratio. The secondary side should have proportionately much thinner wire than the primary side.

      Please do it with proper calculation and if possible take the help of a professional transformer designer.

      Reply

  2. 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.

    Reply

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

      Reply

  3. 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.

    Reply

    • 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

      Reply

  4. 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.

    Reply

  5. Good day swag, Can this circuit be modify to single transformer inverter, what are the components in modification? thanks

    Reply

    • 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.

      Reply

  6. 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

    Reply

    • I am glad you could make it successfully, however the issue which you have mentioned can be difficult diagnose without a practical check, it could be perhaps happening due to instantaneous harmonics generated by the transformer winding or by the load motor winding…you can try installing MOVs at different nodes of the circuit and check if that solves the issue

      Reply

    • 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…

      Reply

  9. 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

    Reply

    • 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

      Reply

  10. 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

    Reply

    • 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…

      Reply

  11. Please, how can I make the inverter frequency stable at 50hz as against 55hz I presently get. I desire it to be 50z. Thanks

    Reply

  12. 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.

    Reply

    • 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…

      Reply

  13. 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

    Reply

  14. 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

    Reply

    • 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

      Reply

  15. 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

    Reply

    • 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

      Reply

  16. 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?

    Reply

    • 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.

      Reply

  17. 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?

    Reply

    • 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.

      Reply

  18. 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.

    Reply

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

      Reply

  21. Thanks Mr Swagatam for the quick response to my question on my modified inverter more grease to your elbows.

    Reply

  22. 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.

    Reply

    • 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

      Reply

  23. 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?

    Reply

    • 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

      Reply

      • 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?

        Reply

        • 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

          Reply

          • 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.

            Reply

            • 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?

            Reply

  24. 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?

    Reply

    • 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.

      Reply

      • 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?

        Reply

  25. 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…

    Reply

    • 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.

      Reply

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

    Reply

  28. 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

    Reply

      • 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?

        Reply

        • 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…..

          Reply

            • 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…

  29. 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

    Reply

  30. 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.

    Reply

    • 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.

      Reply

  31. 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)

    Reply

  32. 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.

    Reply

  33. 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

    Reply

  35. 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

    Reply

  36. 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.

    Reply

  37. 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…

    Reply

  38. 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

    Reply

      • 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

        Reply

  40. 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

    Reply

  42. 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.

    Reply

    • 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

      Reply

  46. 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

    Reply

  47. 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.

    Reply

    • 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

      Reply

  48. 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.

    Reply

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

    Reply

  51. 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

    Reply

  52. 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.

    Reply

    • 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???

      Reply

  53. Hello sir, please between mosfet and igbt which one is better in efficiency and other features assuming they have same spec

    Reply

  54. 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 ?

    Reply

  55. 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.

    Reply

  57. 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

    Reply

  58. 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.

    Reply

      • 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.

        Reply

        • 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.

          Reply

        • 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.

          Reply

          • 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.

            Reply

  60. 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.

    Reply

    • 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.

      Reply

    • 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.

      Reply

      • 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.

        Reply

  62. 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?

    Reply

    • 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.

      Reply

      • 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.

        Reply

  63. 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.

    Reply

    • 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

      Reply

    • 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.

      Reply

      • 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.

        Reply

      • 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?

        Reply

        • 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.

          Reply

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

          Reply

          • 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

            Reply

          • 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?

            Reply

  64. 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 .

    Reply

    • 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

      Reply

  69. 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?

    Reply

    • 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.

      Reply

  70. 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?

    Reply

    • 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.

      Reply

  71. 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.

    Reply

    • 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.

      Reply

      • 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.

        Reply

        • 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.

          Reply

          • 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.

            Reply

            • 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.

  73. 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 ??????

    Reply

    • 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.

      Reply

  74. 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.

    Reply

    • 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

      Reply

  75. GREAT JOB SIR!. i made an inverter,2kva, the input power from the DC was 210w and the output power from AC was 225w while on load( freezer), the calculated efficency was 106%, with any load it was 52%. how could this be. how can i have high efficiency inverter. thanks

    Reply

    • 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

      Reply

  76. 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

    Reply

    • 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.

      Reply

    • 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…

      Reply

    • 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

      Reply

    • 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.

      Reply

    • 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

      Reply

    • 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??

      Reply

    • 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

      Reply

    • 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?

      Reply

    • 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.

      Reply

    • 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

      Reply

      • 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….

        Reply

        • 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.

          Reply

  77. 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

    Reply

    • 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….

      Reply

  78. 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.

    Reply

    • 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.

      Reply

  79. 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.

    Reply

  80. 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.

    Reply

    • 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.

      Reply

    • 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

      Reply

    • 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

      Reply

    • 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.

      Reply

    • 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??

      Reply

    • 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.

      Reply

    • 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.

      Reply

    • 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.

      Reply

  82. 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

    Reply

    • 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

      Reply

  83. 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.

    Reply

    • 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….

      Reply

    • 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.

      Reply

    • 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

      Reply

    • 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.

      Reply

  84. 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.

    Reply

    • 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….

      Reply

  85. Hi sir, I'm talking regarding
    https://homemade-circuits.com/2013/04/how-to-modify-square-wave-inverter-into.html?showComment=1501252519737&m=1#c8767881833588251074
    As per your last comment "Hi Abhishek,

    make sure the PWM frequency is not over 200 or 300Hz.

    for your 600V issue you can read the following article.

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

    and please don't comment under this article because it is flooded with comments and I have to press "load more" button repeatedly…you can comment under some other inverter article" I want to say that, sir firstly I tested it without pwm then I tested the same transformer with my another square wave inverter then output was 360v. And I think this setup have damaged both of my transformer as I tested old 5amp transformer 12v then also the output was 260v, because earlier I had tried both of my transformer with this setup using pwm also and I think my both transformer are now damaged due to this full set (may be high frequency done this damage) please help, and can we have a video call so I can make you understand more easily.
    PLEASE READ FULL AND THEN HELP, I THINK MY BOTH TRANSFORMER ARE DAMAGED DUE TO THIS INVERTER AS I HAVE TESTED IN ANOTHER INVERTER RESULT IS SAME I'M JUST LIKE DEAD. Please tell if video call or WhatsApp is possible.

    Reply

    • 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

      Reply

  86. 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.

    Reply

    • 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

      Reply

  87. 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?

    Reply

    • 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.

      Reply

    • 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.

      Reply

  89. 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.

    Reply

    • 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.

      Reply

    • 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

      Reply

    • 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:

      Reply

    • 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.

      Reply

  90. [URL=http://s1077.photobucket.com/user/drahcir26123/media/testing_zpsvx2lii0a.png.html][IMG]http://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.

    Reply

    • 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

      Reply

    • 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

      Reply

  91. 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.

    Reply

    • 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.

      Reply

    • 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.

      Reply

  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

    Reply

  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. 🙂

    Reply

    • 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.

      Reply

    • 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.

      Reply

    • 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… 😂 😂

      Reply

  98. Hi Innovator, please what is the maximum current that a large appliance can draw from a 100Ah deep cycle AGM battery that will not have a negative strain on the battery. what is the rule for the battery to have long lasting life.

    Reply

    • 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…

      Reply

  99. please sir, i have built 2.5kva/24v inverter that works well for my water dispenser but did not work for my freezer- 1.8A current and 170w input power. why is it not working and what are your suggestion. thanks sir

    Reply

    • 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.

      Reply

    • Thanks sir, the voltage was 236v, Ac current draw using a clamp ammeter was 2.4A while the dc current when the freezer tried to pick was 23.34A but when not starting, it was 4.02A( DC)

      Reply

    • 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.

      Reply

    • 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.

      Reply

  100. 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)

    Reply

    • 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

      Reply

    • 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

      Reply

  101. 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.

    Reply

    • 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

      Reply

    • 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

      Reply

  103. 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

    Reply

  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

    Reply

  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.

    Reply

  109. 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

    Reply

  110. 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.

    Reply

    • 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.

      Reply

  111. 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

    Reply

  113. 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.

    Reply

  116. 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?

    Reply

  117. I think pin 10 of SG3525 can be without connection to negative, just stay free. And if you want, you can add a relay with plus (+) to com and NO or NC depends of state and connect to pin 10…..

    Reply

    • sorry that's not correct, preferably it should be connected to ground either directly or through a capacitor to avoid stray pick and instability

      relay can make it unnecessarily complicated

      Reply

    • Mattlander, it can be done by configuring pin#4 of 555 to positive through a 10k resistor then connecting a BC547 transistor collector with pin#4 of the iC, emitter to ground and base to the shut down high logic through a 10k resistor…..but it is not required because shutting down SG3525 alone will be enough to shut down the output

      Reply

  122. Good day,
    I saw your recent post mr. Ainsworth about sg3525 sinewave/modified sine wave pcb design.
    Please i would like to ask you some questions about pcb design and inverter circuitry and i will be greatful if you give me your time.
    This is my email please.
    abkrmsani@gmail.com
    Thank you.

    Reply

  123. Thank you both, it will be very helpfull, I can send you my email if it is now allowed to attach here.
    Swagatam, I can share a Eagle pcb for automatic slide gate controller from your site, tested and worked, if somebody wants to make it.

    Reply

  126. hello sir i made this circuit but the sine wave is not completely give any advice please.
    How to check inervter wave? without oscilloscope I will share you give mobile headphone and conect pin11 and 14 of ic sg3525 and 10k register in the serise of the headphone we hear the wave sound.sir my English is very weak don't angry on me.sir how to post image
    By me?

    Reply

  128. Hello sir. I really want to appreciate your efforts..your blog have being so helpful to me.
    Sir if I generate a sine wave using an op amp(ua741) and then feed it to the identical transistor(bc547) below will it improve the output? Or should I still use the triangular wave?

    Reply

  129. Hello Sire I want to firstly appreciate your efforts… your blog has really helped electronic novies like me.
    Sire if I generate a sine wave using an op amp an feed it to the two identical bjt(547) will it work? Or should I still use a triangular wave ?

    Reply

  131. In that case I could supply a 48-0-48v to the circuit and use a 45-0-45v transformer because I want to modify this to 6000 watts, I was thinking to use some irf3205, would 6 pairs do?

    6000 watts at 48 volts would be 125amps I'm wondering if I can get that transformer made.

    Reply

  133. Good day sir,
    Please can these two upgrade circuits be incorporated with output pin of SG3524 IC to achieve the same sine waveform?
    If not, please help me out with an upgrade because i have a circuit of SG3524 and wants to upgrade it to a sine.
    Thank you sir.

    Reply

    • Hello Abubakar, yes the concept can be easily implemented with SG3524 based circuit also, in fact with any squarewave inverter….you can use a 4047 inverter, TL494 inverter 4017 inverter etc….the PWM/BJT stage explained above is a universal sinewave generator design

      Reply

    • a simple LC network at the output of the transformer would help to neutralize the harmonics and improve the waveform, although this may not be entirely critical

      Reply

  141. since the SPWM method is better I would like to draft up the circuit for that also but I am having probs finding triangle wave circuits to match the 50hz and 200hz output I need at the correct voltage which should be 5v I assume.

    You could help me out with that I would go through your page and do some drawings of the tested circuits but i'm not sure of all those you tested, you could send me some links of circuits you dont have time to draw up and I would do them and some pcb also if you like.

    Reply

    • a 555 IC astable circuit could be used for obtaining reasonably good triangle waves, it could be extracted across the timing capacitor of the astable.

      two such circuits could be built for developing the slow/fast triangle waves and integrated with the opamp inputs

      5V may not be critical, although a 7V supply for the 555 ICs would enable you to get 5V triangle waves…

      Reply

  144. I read it over just now I understand I can use the basic 3525 diagram and the bjt output stage and also feed the pwm input to the pwm input section on the bjt stage.

    What I dont understand is the SPWM, I understand the concept just dont know the frequencies that I should feed the opamp with, how high and how low should the frequencies be by guessing I would make the fast one 200hz and the slow one 50hz my expected output is 50hz at the inverter's output.

    Reply

  145. I just saw this post I havent been here for some time, in the past I normally asked you for pcb of the circuits you make but it would normally be a case that your too busy. I have been doing some practice over the last couple months and I am now successful in building designing the pcb's and also making m own boards, I know im not as good as the professionals but for the simple circuits I build they work well for me.

    I was just reading this article and was trying to put everthing together so I could make a pcb but I think I am not understanding something, ouu uploaded a basic design with the 3525, I am now wondering where should I send 2 output pins on the 3525 to:

    1) An opamp?
    2) the same bjt stage you have?

    or would I need to make 2 triangle oscialator circuits to feed 2 opamps then send the outputs to the base on the bjt section of the inverter and also connect the output from the 3525 to the base of the bjt's also.

    Reply

    • 1) it's clearly indicated that the 3525 outputs are supposed to join with the "BJT/mosfet stage"….meaning with the two 10k resistors at the bases of the BJTs…

      the opamp and triangle wave stages are associated with PWM generation.

      Reply

  149. Hi Mr swagatam,
    I really appreciate your grate jobs and ideas shares with everyone. MORE POWER TO YOUR ELBOW AND GOD WILL BLESS YOU SIR.

    I've done many of your design and everything works perfect.

    I want to try this as well and I will need you to guide me through if any challenge. once I finish I will share

    Reply

  152. In the ic555 circuit what is the function of the pot and what single resistor will be used in place of it for generating 4 times the base frequency? and also will i eliminate the feedback feature of the sg3525 using a 6-0-6 500ma transformer 3.if i want to add more mosfet in parallel will i use seperate 50k resistor at it's gate 4.if i build this circuit will it produce a mains ac similar waveform that can get rid of the humming of inductive loads like fan when connected to modified sinewave? thank you.

    Reply

    • the pot is used for setting up the PWM for the inverter, and it cannot be replaced with a single resistor since it needs to be precisely adjusted for fixing the RMS value.

      the fixed resistor determines the frequency

      yes the feed back mess can be eliminated if the above explained method is employed, but make sure the all the circuits are supplied from a fixed voltage source using 7812 IC.

      parallel mosfets can be added without any modifications.
      with some filtration at the output the results could be quite similar to pure sinewave

      Reply

    • Thanks Swag for your devotion and dedication …

      Some few follow up questions,
      -How will i know that the adjustments i Have made with the pot of the pwm are optimal?
      -I thought this circuit was an ultimate pure sine wave inveter schematic, after reading your reply to this comment I was deviated from what I knew, My question is thus,
      Which filtration need to be added at the output to make the output similar to the pure sine wave?

      Reply

    • Buberwa, it is the ultimate sinewave circuit because it is easiest and the most effective design according to me.

      PWM must be set until the output of the transformer shows 220V or reaches the required correct output voltage level.

      initially you can add a 0.22uF/400V capacitor and check its response on oscilloscope.

      do all these only if you are well versed with all the basics of electronic..otherwise please do not attempt this circuit.

      Reply

  153. hello swag…thanks for your time and effort you take to answer questions and designs, i would like to ask this ..can the arduino be used to generate the oscillation to drive the mosfets and the pmw to feed the two BC547 ?

    Reply

    • thanks solomon,

      according to me, an Arduino can be programmed and used for generating the basic mosfet oscillations and also the PWM oscillations together from its respective pinouts.

      Reply

  155. Hi,
    First of all thank you for publishing that much of hard work free for any body to use. Also could you please tell me how you limit or achieve 4-5 pulses in each 50Hz cycle. Does it happen automatically once you connect BC547 to SG3525. Thanks,

    Reply

    • Hi, Thanks, it is initiated when PWM is fed at the bases of the two BC547 transistors shown at the bottom of the first circuit.

      The PWMs can be generated using the recommended circuits using IC 741, IC 555

      Reply

    • Dear Mr. SWAGATAM MAJUMDAR
      First of all, I would like to thank you for your dedication to help others.
      Thanks for publishing the modified sine wave inverter SG3525. Some days back you published a modified sine wave project with TL494. I wish to assemble one. Could you please suggest me, which one is better with features to assemble for my home? I need an inverter with capacity of 500 to 1000watt.
      Thank you, Benjamin

      Reply

    • Thank you Benjamin,

      both the ICs are significantly similar with their working specifications and features so it doesn't make much of a difference as far as performance is concerned. You can try the one which is more suitable to you…

      the power output will depend on the mosfet specs and the battery AH rating

      Reply

    • Hi…mr. swagatam appreciate your goid works hobys electronics i like those simple sinewave generation of inverter is it posible to simulate the circuit before i attemp to build im trying using proteus but not working only the pwm 555 side working but sg3525 configuration not work im using sg2525 proteus model what simulator you use to simulate the circuit?

      Reply

    • Hello mr. Swagatam i try to simulate the complete circuit using proteus but dosent work only pwm 555 working sg3525 in output trabsformer not work im using sg2525 proteus model

      Reply

    • Helo rynyahu, that's the reason I never use software for testing any circuit, I prefer simulating the design inmy brain and then implement it practically…if you are really interested to succeed with any electronic then you must first understand the design from the core and then build it practically using good quality parts.

      If You are depending on a software you would be wasting your time.

      or alternatively you can try applying any other SG3525 circuit from the internet and see if it responds in the software, there are many versions on the net.

      Reply

    • hello swagatam thanks for the reply mr. is the pwm circuit will work for all square wave inverter i have a square wave made myself i plan to use your pwm circuit only using those BJT buffer stage mosfet driver stage

      Reply

    • Ok thanks swag…one more thing is this circuit can be added to any squarewave inverter to modify as closes to main ac sine wave without any isue? I plan to add this circuit to my square wave inverter

      Reply

    • Shalom to you sir swagatam thank for a kind reply my another question is why the sg3525 circuit as shown above has not implemented with a feedback circuit for stablization of the output voltage lets say a 220vac should be stable during load or even at its maximum power of load the output voltage will be regulated or corrected

      Reply

    • Shalom rynyahu, the automatic output voltage regulation is an optional feature which is not crucial, because if the inverter trafo is selected correctly its output will never exceed 250V, which any load can handle with comfort.

      Reply

    • shalom sir swag you mean if my supply voltage to the inverter circuit is 12VDC the transformer to use will be like 9-0-9 center tap since it is pushpull or if my supply voltage is at 24VDC my trafo should be at 18-0-18 center tap am i correct? at this point feedback circuit is not crucial at all handing the load without dropping the output voltage?

      Reply

    • Shalom Rynyahu, you are right, keep the trafo input winding value almost close to the battery value for getting a correctly optimized output mains, but this may be true only for non PWM circuits, for PWM circuits the trafo voltage rating should be much lower than the battery value, and here the PWM should be adjusted for the setting up the correct output level.

      Reply

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