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Convert a Square Wave Inverter into a Sine Wave Inverter

Convert a Square Wave Inverter into a Sine Wave Inverter

The post explains a few circuit concepts which can be employed for converting or modifying any ordinary square wave inverter to a sophisticated sine wave inverter design.

Before studying the various designs explained in this article, it would be interesting to know the factors which typically makes a sine wave inverter more desirable than a square wave design.

How Frequency Works in Inverters

Inverters basically involve  frequency or oscillations for implementing the boost and inversion actions. The frequency as we know is generation of pulses at some uniform and calculated pattern,  for example a typical inverter frequency may be rated at 50Hz or 50 positive pulses per second.

The fundamental frequency waveform of an inverter is in the form of square wave pulses.

As we all know a square wave is never suitable for operating sophisticated electronic equipment such as TV, music players, computers etc.

The AC (alternating current) mains that we acquire at our domestic mains outlet also consists of pulsating current frequency, but these are in the form of sinusoidal waves or sine waves.

It's normally at 50Hz or 60Hz depending upon the particular country utility specs.

The above mentioned sine curve of our home  AC waveform refers to the exponentially rising voltage peaks which constitute the 50 cycles of the frequency.

Since our domestic AC is generated through magnetic turbines, the wave form is inherently a sine wave, so doesn't require any processing further and becomes directly usable in homes for all types of appliances.

Conversely in inverters, the fundamental waveform are in the shape of square waves which needs thorough processing in order to make the unit compatible with all types of equipment.

Difference between Square Wave and Sine Wave

As shown in the figure, a square wave and sine wave may have identical peak voltage levels  but the RMS value or the root mean square value may not be identical. This aspect is what that makes a square wave particularly different from a sine wave even though the peak value may be the same.

Therefore a square wave inverter working with 12V DC would generate an output equivalent to say 330V just like a sine wave inverter operating with the same battery  but if you measure the output RMS of both the inverters, it would differ significantly (330V and 220V).

The image incorrectly shows 220V as the peak, actually it should be 330V

In the above diagram, the green colored waveform is the sine waveform, while the orange depicts the square waveform. The shaded portion is the excess RMS which needs to be leveled of in order to make both the RMS values as close as possible.

Converting a square wave inverter into a sine wave equivalent thus basically means allowing the square wave inverer to produce  the required peak value of say 330V yet having an RMS just about equal to its sine wave counterpart.

How to Convert/Modify a Square Waveform to Sine Waveform Equivalent

This can be done either by carving a square wave sample into a sine wave form, or simply by chopping a sample square waveform into well calculated  smaller pieces such that its RMS becomes very close to a standard mains AC RMS value.

For carving a square wave to a perfect sine wave, we can employ a wien bridge oscillator or more precisely a "bubba oscillator" and feed it to a sine wave processor stage. This method would be too complex and is therefore not a recommended idea for implementing an existing square wave inverter to a sine wave inverter.

The more feasible idea would be to chop the associated square wave at the base of the output devices to the required RMS degree.

One classic example is shown below:

The first diagram shows an square wave inverter circuit. By adding a simple AMV chopper we can break down the pulses at the base of the relevant mosfets to the required degree.

simple square wave inverter circuit

Modified square wave to sine wave equivalent inverter version of the above circuit.

Here the lower AMV generate pulses at high frequency whose mark/space ratio can be suitably altered with the help of preset VR1. This PWM controlled output is applied to the gates of the mosfets in order to tailor their conduction into the stipulated RMS value.

How to Modify a Square Wave Inverter into a Sine Wave Inverter

Expected typical waveform pattern from the above modification:

Waveform at the mosfet gates:

Waveform at the output of transformer:

Waveform after proper filtration using inductors and capacitors at the output of the transformer:

Parts List

R1, R2, = 27K,
R3, R4, R5, R6, R7,R8, R9, R10 = 1K Ohms,
C1,C2 = 0.47uF/100V metallized
C3, C4 = 0.1uF
T1, T2, T5, T6 = BC547,
T3, T4 = any 30V, 10amp mosfet, N-channel.
D1, D2 = 1N4148
VR1 = 47K preset
Transformer = 9-0-9V, 8 amp (specifications must be selected as per the output load for correct powre optimization)
Battery = 12V,10AH

Getting Better Efficiency Rate

The above conversion or modification will provide around 70% of efficiency with the achieved RMS matching. If you are interested in getting better and precise matching then probably a an IC 556 PWM waveform processor would be required.

You would want to refer to this article which shows the principle behind modifying a square waveform into a sine waveform using a couple of IC555.

The output from the above mentioned circuit can be similarly fed to the gate or the base of the relevant power devices which are present in the existing square inverter unit.

A more comprehensive approach may be witnessed in the this article where an IC 556 is used for extracting precise PWM based modified sine wave equivalents from a square wave sample source.

This waveform is integrated with the existing output devices for implementing the intended modifications.

The above examples teach us the simpler methods through which any existing ordinary square wave inverter may be modified into a sine wave inverter designs.

Converting into an SPWM

In the above article we learned how the waveform of a square wave inverter could be optimized for getting a sine wave kind of waveform by chopping the square wave into smaller sections.

However a deeper analysis shows that unless the chopped waveform is not dimensioned in the form of SPWMs, achieving a proper sinewave equivalent may not be possible.

To satisfy this condition an SPWM converter circuit becomes essential for carving out the most ideal sinewaveform from the inverter.

The following diagram shows how this could be effectively implemented with the designs discussed above.

SPWM conversion for a square wave inverter

Through one of my earlier articles we understood how an opamp could be used for creating SPWMs, the same theory could be seen applied in the above concept. Two triangle wave generators are used here, one accepting the fast square wave from the lower astable, while the other accepting slow square waves from the upper astable and processing them into corresponding fast and slow triangle wave outputs, respectively.

These processed triangle wave are fed across the two inputs of an opamp, which finally converts them into SPWMs or sine wave pulse widths.

These SPWMs are used for chopping the signals at the gate of the mosfets which ultimately switch the waveform over the connected transformer winding for creating an exact replica of a pure sine waveform at the secondary side of the transformer through magnetic induction.


About the Author

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

339 thoughts on “Convert a Square Wave Inverter into a Sine Wave Inverter”

  1. Howdy, Friend! Interested to Learn Circuit Designing? Let's Start Discussing below!
  2. hello mr Swag,
    I found your site from Google. A lot of stuff here, it is very good!
    I know that the Square Waveform inverter needs a classical iron (50hz) transformer to work.

    I have a dumb question.. do a spwm inverter (which pwm frequency is for example 1 khz) also need
    a classical iron transformer OR it needs a ferrite toroid transformer.
    I am confused because of the pwm’s high (ralative to 50hz) frequency.

    thank you mister!

    Petros Chris

  3. Thank you very much Sir for the thump’s up and for replying me. The issue is that am using a stabilizer container to cover the inverter…thus it wount contain upto 24(12pairs) of IRFP150N because the Vero Board will be too long. I learnt there are higher IRFP MOSFETs, but i dont know the numbers and how many watts they dispense that give 3kva with lesser pairs.

      • Ok sir, but 3 MOSFET of IRFP150N will only give me 750watts. I need the specification of 3or4 pairs of MOSFET that can give me upto 3kva, please Sir.

        • Steve, if you intend to use the mosfets without heatsink then it will 250 watts each…but with heatsinks, they will be 40 x 24 = 960 watts each according to me.

  4. Good morning Sir, ive successfuly built a 1000w inverter with a 24-0-24 to 240v transformer, using a 4pair IRFP150N MOSFET for the Power Stage and its working well. I need to build another 3000w inverter but if i use the IRFP150N MOSFET it will be too long and ridiculus, so please which MOSFET can i use that will make it easy? Thank you Sir

    • That’s great Steve, appreciate your efforts.

      you can use IRFP150N mosfet for achieving 3kva, without any problems, it won’t be an overkill..

      if possible please send me a small video clip of the working inverter which you have made to my email…I’ll be grateful!!

      my email is homemadecircuits @ gmail.com

  5. Hello sir, i asked some questions in one of ur post and i see no reply, let me ask u the same questions here:
    1. In choosing or selecting MOSFETs, what must i consider, is it the volt or the amp of the MOSFETs?
    2. Can i use stabilizer transformer to connect with my inverter circuit?, or does a stabilizer and inverter has different pattern of winding

  6. Sir I hv some questions-
    1. instance of ( R1,R2,R3,R4,R5,R6,T1,T2,C1,C2 the 50Hz oscillator circuit)
    can I use a 4047 oscillator with 50-60Hz?

    2. instance of (R7,R8,R9,R10,C3,C4,T5,T6,VR1 the pwm circuit) can I use a 555 PWM circuit?

    3. I want to make 4047 for oscillator, with 50-60Hz and then can integrate 555 PWM with it as like as u shown the 2nd circuit, is it possible?
    4. if possible then what ll be 555 PWM frequency?
    sir plz make me understand
    Thank u

  7. Sir please help me to convey the details regarding the conversion of 12 volt 50 hz square wave signal to 12 volt 50 hz sinusoidal wave…pls help me in the designing part ,

  8. Hi sir, I'm now double stressed, I, this time recently checked only the square wave part of circuit with my old 12-0-12 5amp transformer and this time I got 266v even without pwm, I really think that the circuit and 555pwm have damaged both of transformer now what to do? This time life sucks ?.

  9. Hi sir, every thing else is going good now but the LEDs are still fusing because of high voltage 260v(without load) as you know with loads it's 230v in mine case (refer to upper comments) and I can't use 9-0-9 transformer because I had bought 12-0-12 10A far earlier, and the voltage problem is also due to that reason I know. So what to do now? Can I use a converter shown in your blog (anyone from your blog) for 12v to 15v? Is it safe I'm positive towards this regard, please read full and reply soon.

    • Hi sir, could you please help me with some other idea with this matter. Read older comments for revising summary of problem. Please let me know if you have any help for me

    • there's no other idea, either you use the 741 circuit which is suggested to regulate the output, or change the trafo.

      or alternatively you can buy another 12V battery and put in series with your present battery to get 24V and use this 24V with your 12V trafo…then adjust the PWM to get 240V at the output

    • Hi sir ???new problem arised, today I checked my circuit without pwm(only square wave circuit) and multimeter was showing 595v to 600v output and then by connecting pwm I tried it to adjust then it showed "1" means limit crossed. Earlier this problem was not there why is it happening even without pwm, and also with pwm. This problem happened only today, please tell me what is wrong now. I'm littrally very stressed ?, this was my holiday project and holidays are going to be over.
      ??☹️my electronics role modal please help me. Please.

    • Sorry sir, I'm commenting again here but 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.

  10. Hi sir, my transformer is of good quality it's made by shopkeeper on order its big and weighs 8kgs, sir yesterday I added new mosfets and increased them in parallel but when tested no output was there (fluctuations) only some stabilizer like abnormal sound comming when I removed then also conditions were same,I'm very stressed.I think may I'm these problems are because I'm using zero pcb (pcb with square boxes and predefined holes) and not the copper claded, and also due to some improper soldering, because transformer is good. I have written thanks because everytime you give true knowledge and guidance. PLEASE reply soon.

    • Hi Abhishek,

      if transformer is good then it should take the load. and the voltage should not drop…. I am sure something is not correct in your circuit or the parts which I cannot identify from here.
      adding mosfets will not help at all, because it's not correct ,a single pair of IRF540 can handle upto 200 watts to 500watss easily.

      try with BJTs if you are not able to use mosfets…try with TIP142 instead of the mosfets

    • Hi sir I have replaced the lower pwm with 555pwm as you advised and it's good. I have adjusted it without load on 240v but when I connect 3 Watt incandescent bulb the output dropped the voltage by multimeter was 178.so how to adjust it whether while adjusting I have to also connect a load then the voltage without load must come upto near 300v what to do master.

    • Hi Aabhishek, since this is a simple circuit and does not employ any load control circuit, therefore the best way to adjust the PWM is by connecting the load, and anyway the voltage which you may see in your meter without load may not be correct, because the meter will always show a much higher voltage without load due to its high impedance nature, therefore the best way is to adjust the preset with a load connected, and remember I had told you to use a 9-0-9 trafo, at 10 amps and a 12V 7 to 10AH battery fully charged.

    • Hi sir, now I can power mobile charger and 3w bulb (tested) on inverter but when I connect 7w LED bulb the bulb is not glowing and frequency sound increases.what to do sir?

    • Aabhishek, something is not correct in your circuit, it seems the trafo is not saturating correctly, and this can happen when either the transformer or the battery or both are not matching correctly.
      when you connect ammeter in series with the battery the meter should show a current equivalent to the load current.

    • Hi sir I think led bulb might be fused due to high voltage 260v ac, when i connect 3w bulb the voltage goes to 230v and when connecting my phone charger then voltage drops to 215 v what to do? Is there any way you can suggest so I could use this inverter as a good inverter with no further problems or issues. PLEASE HELP. So finally I can say you thanks for this project.

    • Hi Aabhishek, LED bulb are rated to work with 285V so it cannot fuse at 260V.

      Your transformer is not taking the load due to lack of amps, change the transformer with a good quality heavy duty transformer…in todays market most transformers are falsely labelled…for example 3 amp trafo can be seen labelled as 5 amp…no need of saying thanks

  11. Hi swagatam sir, is it possible adding mosfet in parallel with reducing the chances of MOSFET damage and also reduces mosfets heat?

    • You must first find out why your mosfets are burning if it's due to overloading then you can you can add parallel mosfets, but I don't think it's due to overloading.

      I hope you are my following my suggestions and not doing just anything haphazardly???

    • No that's not possible, in your mosfets can get damaged due to a duplicate mosfet, static electricity from your hands, wrong pin connection, drain short circuit or perhaps from reverse transformer emf if diodes are not connected

    • Hi Abhishek, the buffer stage BC547/BC557 was specifically introduced to keep the mosfets safe, but since you were having difficulty in configuring them therefore I allowed you to try without it…but I think it should be included, so better put it back in place as shown in the diagram, I'll update the diagram soon and make the stage simpler by removing the extra diode at the emitter of the BC547.

      And remember you shoold NOT make the design on a breadboard…use a strip-board and make it by soldering…

    • Hi sir.,ok I will do it again and I'm using zero pcb and always solder, no breadboards!. Hope doing this will help, sir I really respect you and your knowledge you are like my favourite teacher.

    • Sir in my PCB there is no space to put those bc547 and 557 STAGES, so what to do I really want to make this inverter Perfectly working. PLEASE HELP ME sir.

  12. Hi swagatam sir again problem even with the modified version of this inverter (see last comment) which you approved when I removed mosfets it was giving 300v output without using pwm circuit but the transistors in first oscillator were becoming hot so you suggest me an alternative, and I have changed mosfets 2 times from starting day and till now. Working without mosfets. Im using 12-0-12 10A transformer and 7.6ah battery. See last conversation for circuit and tell me an alternative this is first time I'm having problems in making something. I'm using 12-0-12 10A transformer.

    • Hi Abhishek, this is such an easy circuit, not sure why you are getting so much of problems, may be because you are doing it without understanding the concept, or using damaged parts.

      By the way who told to remove mosfets??? how can you drive the transformer without the mosfets??

      I am not able to understand what exactly you are doing….

      I would advise that you first thoroughly understand the working of the two circuits and all the parts and only then proceed.

    • Hi sir,
      Can I use transistor Darlington pairs instead, of irf540. May be the seller from whom I take irf540 has given damaged mosfets.

    • Hi Aabhishek, yes you can definitely do that, that's what I had recommended you earlier…..you can use 2N2222 and 2N3055 in darlington mode…or any other similar combination will do

  13. Hi sir, I think you haven't focused on my question, I WAS ASKING " can I make this modified sine wave inverter by not using the upper bc557 and bc547 stages, diodes and all, by using the main upper AMV and lower pwm, and mosfets, no bc557 and bc547 stages , as these things are creating complications." * I MEAN IF I REMOVED THE BC547 AND 557 STAGES AND JUST USING UPPER (MAIN AMV) AND LOWER PWM AND MOSFETS ONLY. PLEASE REPLY FAST TILL AFTERNOON PLEASE MO ?.

  14. Hi sir, when I test pwm, with 16v supply separately, it's out put is 6v,ac,and the output can only be measured when I connect only one prob of multimeter to the capacitor output , when I connect both probes output on screen is 0v, is this normal,?
    Another question is that only lower circuit is said to be pwm or the upper bc 547 and 557 and 1n4007 circuit also a part of pwm

    • Abhishek, your method is incorrect. You must connect the meter probes across the collector/emitter of the transistor…and the meter should be in the DC range NOT AC range. and the measured volatge must vary from some minimum value to maximum value in response to the pot rotation.

      The Bc547/557 is not in the PWM section.

      you can try the first circuit from this article…connect the LEDs and see the effect of the PWM on the LEDs..if it illuminates from fast to slow and vice versa then the circuit working OK.

      after this you can reduce the capacitors to 1uF for fast PWM..


    • Hi sir, one question can I make this modified sine wave inverter by not using the upper bc557 and bc547 stages, diodes and all, by using the main upper AMV and lower pwm, and mosfets, no bc557 and bc547 stages , as these things are created complications. Please reply as as possible.

    • You can try it as shown in the first diagram, make sure to use 1K for the gate resistors and put 1N4148 diodes parallel with these resistors in the following manner:


  15. Hi sir, yesterday night I tested my above circuit by 12v battery for adjusting the 50k preset with multimeter connected at output of transformer, so in first round the voltage was going on decreasing from 210 to 90v ac, In 2nd round the output was 250v and suddenly the point where I had connected the negative terminal catches sparking and fuse burnt,so I removed and again connected battery negative (to point where pwm -ve, oscillator-ve and both sources of MOSFET were connected together) but again that point shorted sparked. I'm using pcb (not printed one), can you assume what is problem or which part should I check. Please help me

    • Abhishek, sparks should never come,,,it means there's a short-circuit in your circuit or something is not working correctly.

      first make the basic circuit without the PWM….and make sure it produces 250 to 300V and is able to illuminate a 60 watt bulb very brightly.

      after this check the PWM circuit with a DC voltmeter connected across collector/emitter of any one of the transistors…the Dc V must change as you vary the 50 pot. also confirm the frequency of the PWM with a frequency meter.

      If you are having problems with a transistor oscillator you can replace it with a IC555 PWM circuit which is much easier to adjust

    • Hi sir, I removed the second AMV circuit and checked everything in first upper circuits for shortings using multimeter I found in one MOSFET source and drain of that mosfet beeped, while in other this was not happening, so I think shortings of source and drain shows that mosfet is faulty, so replacement of one MOSFET will be OK or I replace both, how to protect new mosfets from further defects. Please reply fast. I'm really interested in making this inverter perfectly working.

    • Hi sir the link you sent is seen and understood but I want to ask that after replacing MOSFET, now can I check the inverter or I need to give some protection to the mosfets, which diodes can I use with mosfet to protect them. Can I test inverter without providing any diode protection to mosfets.

    • Abhishek, although all mosfets are protected internally with diodes, still you can place diodes across the primary of the trafo… from center tap to the outer taps..cathode will go to the center tap, and anode to the outer taps…you will need two diodes from ceter to the outer taps.

      1N4007 diodes can be used for the diodes.

  16. Hi sir, every time you are so helpful, I want to ask that can you explain the procedure for adjusting preset (50k I have used) without damaging any thing. PLEASE HELP ME, tell me a safe method. How to adjust it.

    • Hi Abhishek, the procedure is simple.

      initially keep the preset slider at the center.

      Now switch ON the inverter and connect an AC voltmeter at the output of the transformer for measuring the voltage.
      after this slowly adjust the preset until the output voltage settles down to 220V.

      I hope you have used a lower rated 6-0-6V or 9-0-9V trafo for a 12V battery

    • Hi sir, I'm using 12-0-12 10A,transformer for 12v 7.6ah battery. Is it OK? Will the circuit work perfectly. OR any correction I should make. PLEASE REPLY FAST.

    • 12-0-12 will produce 180V output with PWM activated…you will have to use a 6-0-6 10 amp or 9-0-9 10 amp trafo for getting proper results

    • Hi sir, I only have 12-0-12 10A transformer, you must have specified in article that it's necessary (mandatory) to use 9-0-9 v transformer this is very disappointing.Now the problem is budget and I already spent rs 1050 on that transformer, shopkeeper will also not take that back because it was made on order, can you please tell me a solution so I could get 220v to 230v AC from the same transformer i.e 12-0-12, should I increase input if yes, how? Please help, I couldn't ask my parents for this. PLEASE HELP.

  17. Hi sir, please reply fast,can I use 820pf capacitor instead of 680pf, and 50k preset instead of 47k in second circuit, because 680pf capacitor are not available in market. And tell me how to adjust the preset and from where to measure the rms to adjust preset, explain me whole process please. PLEASE HELP ME.

  18. Hi sir, I'm using 50k preset (not the potentiometer) and 820pf capacitor instead of 680pf capacitor, is it OK? How to adjust the preset, what is the process.

  19. Hi sir,
    Can you tell me how to connect preset in this as the circuit shows,all three terminals are connected at different places, I don't know how to connect, can you please assist me through any image or photo explanation, please reply fast.

    • Hi Abhishek, the arrow symbol indicates the center pin of the preset and the outer two points correspond to the outer two pins of the preset…

  20. hi sir,
    please tell me how to tell shopekeeper if want transformer for 100 to 150 watts inverter? ,as if i say them i want 12-0-12 10A transformer they say tell us "va" .thay dont understand me,tell me what should i say them in their language if i wat transormer for 150w inverter ?

    • Hi Abhishek, If they are asking for VA, then tell them the value by multiplying 12 x 10 = 120 watts….. there's nothing too critical about it….

  21. Abhishek, those are not Darlington pairs, those are arranged to generate a push pull action on the mosfet gates…they are in NPN/PNP formation

  22. Thanks for posting such a nice and useful project.

    I want to make an inverter of 1000-Watts or higher, could please guide me what components mainly required
    Best Regard

  23. Sir, I have already built this inverter. But, It is sometime giving above 230v output, depend on the battery AH I use.
    Colud you help me with any output filter, so that the out will be constant at 220v to 230v?


    • Aminu, it is not required as long as the output is between 210V and 240V, it is quite normal.

      If you add an output regulator it will make your design unnecessarily complicated

  24. Hi there, I have read over your blogs and am very impressed with your electronic knowledge, I have a question for you, I will be running two dc to ac inverters rated at 10,000 watts surge and 5,000 watts constant running watts each. They are however MSW ( modified sine wave) I am wondering if there is a circuit I could build for each of these that could convert them more closely to a standard sine wave to make them safer for use for sensitive electronics ETC, computers, tv,s video games and the like? I am familiar with basic and communication electronics but rather weak when it comes to inverter modifications. the inverters are a HF( Harbor Freight) product that carry the CEN-TECH brand name. I havent been able as of yet to find a schematic for these units. It would be greatly appreciated for any help you could offer…thank you in advance

    Mad Scientist

    • Thanks Eric, It is definitely possible using the concept explained in the above article, however first you will have to figure out how the mosfet stages are configured in your existing inverter, and then target the right mosfets for integrating the explained circuit theory…otherwise you may end up ruining the entire inverter or create catastrophic results.
      You can also try a much improved version using SPWM which I may soon present in one of my future articles in detail. In the meantime if you need any help you can feel free to consult me

  25. Good day sir, the VR has two legs or three legs. Bcos the one i have is three legs but the one on diagram is just end to end with the transistors. Thanks

  26. Yes Sir, it has.
    But what I mean is this, UPS works on little corrent battery i.e 7ah and it's able to operate a computer that needs high watts ?while majority of inverters cannot.
    I learn this due to the suggestion you made to start our homemade inverter with big ah battery ? e.g 100ah or 200ah to operate 100 watts which is not as big as deck top.

    thanks you Sir.

    • your assumption is not correct, an inverter can be equally efficient just like an UPS as far load handling is concerned…except the waveform and automatic functions which are the more enhanced in UPS.
      please show me where did I say that a 100 watt load would require a 100 AH battery??

    • A 100 AH battery will be required for a 100 watt load if a back up of 10 hours is expected….so I might have said on that context.

  27. Sir this is Aminu.
    Sir I wonder why UPS can operate computer ? using a 12v 7ah battery ? while inverter cannot work with such a higher watts device on 12v 7ah.

    • Aminu, an UPS also has a built-in inverter so that's a wrong assumption.

      without an inverter the UPS cannot create the back up supply

  28. Hi friend I like your projects. I actually want to build and try your design. So, for the first circuit in which you used two power mosfet , can i replace them with IRF150n? If so, what will be the output power. And also kindly tell me if i use IRF150n with the second schematic contains four transistor what will be the power then? Thanks. You always helped me alot.

    • Thank friend, the output will depend on the wattage rating of the transformer and the battery AH capacity…the mosfets rating should be selected such that they are able to comfortably handle the power consumed by the transformer and the connected load.

      only the mosfets are responsible for power delivery, other transistors are only for buffering they need not be changed

  29. Sir
    I have su-kam inverter trusty . 1500 w . 24 v .when connecting to home all fans making noize . What should i do to remove that noize from fans . Shall i add capcitor to the out put . If yes which type and size

    • yes you can try it…..you can see the following example design and follow the configuration:


  30. I would like to know if this circuit has been implemented and tested as i am experincing some problems and would like to brain storm for possible rectifications from those who have implemented this exact circuit.

  31. Sir what I mean is that, If I used the 2nd circiut the fan is not operating but the circuit can operate many appl and If I remove PMW part and leave AMV and BC547/557 the result is the same. whhile with the first circuit (squar wave) that has no bc547/557 stage, the fan can work with little noise.

    • Aminu,

      connect a 60 watt incandescent lamp to the inveter output and check its brightness with PWM ON, and without PWM, this will tell you whether or not PWM is reducing the output power?… and why the fan may be finding it harder to rotate with the PWM ON.

  32. Sir,
    I did it.
    I used this ic555 configuration, as you suggested me alias.


    After I connect this to the AMV, I can vary the volt from 0. to 220v and above.

    I dont realy know if, my circuit is faulty or not.
    I tried many electronic app and they work, But the fan is still incline to operate.

    I wondar why, the First circuit (Square wave) can operate the fan with little noise, While if I connect the PWM part (including this newly adopted i.e IC555 part) it woun't operate.

    Anyway, Sir, Your help is always appreciated and Iam very much proud of you Sir.

    Thank you once again.

    • Aminu, the PWM is chopping the actual 50 Hz, that means it is actually reducing the overall power….so this in turn means that the transformer needs to be more powerful for a PWM inverter because the PWM is cutting off 50% current…so this could be the issue…try another trafo with higher wattage and check the response.

  33. Ops, Iam wrong Sir.

    The volt is not 220-240 its almost 200v peak and almost 195v the low, so, its not stable. It is shaking ups and down within a second.
    This is why the multimeter is reading wrongly.

    • Aminu as long as you don't confirm the lower circuit performance you'll always be in doubt regarding the circuit proceedings, I think you should try replacing the lower AMV with a 555 IC AMV, I'll try to update the modification soon in the article, may be tomorrow, you can then try it out and check the response.

  34. I did it Sir,
    But the test is done with 0.2uf i.e 224j instead of the one you suggested, because I have only a pair of 104 which was used in PWM.

    Based on this test i can see the volt is ok, Its around 220 to 240 now with PWM but I tried to adjust the pot and nothing change even if the pot turned to the end of each direction.

    But I load only 26watts economy ligh bulb.

  35. Sir,
    Right now I do some changes as follows,
    I used 7.2_0_7.2 tranfo 650Va.
    I chanced mosfet to IRF3205.
    I removed pwm.
    finaly, the fan operates with some low noise if compared with my last test.

    and if I connect pwm part, the fan fails to operate and produce louder noise.

    Thank very much, its few staps remain to build a very reliable low cost inverter.

    • Aminu,

      PWM will reduce the RMS of the output voltage therefore the transformer's primary rating should be lower than the battery voltage, 7-0-7V is a good trafo but its current should be at least 10amps, and for higher loads the battery AH should be at least 10 to 20AH fully charged.

      If the PWM frequency and duty cycle is high, the fan will make noise, so adjust it until the noise is almost gone.

      reduce the lower AMV capacitor values to 0.1uF to reduce the frequency and adjust the pot to optimize the duty cycle, and then see the response.

  36. Sir,
    with pwm the AC output volt is between 180v to 111v or even lower, but without pwm the volt is alway above 200v AC.

    I used three transfo
    1. 7.2-0-7.2 transfor removed from 650va
    2. 12-0-12 5A
    3. 500va transfor that has no details printed on it.
    each showed the same result.

    I used 12v 20AH battery.

    Sir, The inverter has no any other problem now because I discovered them and solved them today.

    But, the issue of operating Fan is still unchanced.
    the fan is 50watts and its only producing loud soud without turning, even if I used my hand to help it to turn, it won't.
    and this problem is the same with both oper and lower circuit.

    Thank you Sir for the help.

  37. Aminu,

    remove the PWM feed from the lower circuit, and check the response.

    and what's the battery AH?

    and what's the transformer amp rating, let me know about these, I'll try to troubleshoot.

    would it be possible for you to use power BJTs instead of mosfets just for testing sake? because BJTs are much easier to handle than mosfes.

  38. Sir,
    I am refering to this recent one that you asked me to build and I builded it. I dont mean it has problem, Iam the one coursed it.

    I found the track and jumper are borning and the mosfets are getting hot instantelly when i load a higher watts. so through your help all those was solved.

    base on my check I discovered the courses of the problem as follows: the battery power is set to cross over the circuit then goes to transf and it is also solved through the procedure I sent in the last mail.

    Sir, still Iam exeriencing some problems that i dont know their source.

    1. one of the mosfet is getting hot If i load the
    laptop or any higher wattages appilience like
    100watts bulb.

    2. my multimeter is ok, but when connected it to
    the inverter in order to test the AC output volt, the multimeter is reading wrongly and if connected to main AC its reading normal 220v or 219v.

    3. still the inverter can not operate Fan.

    As usual, I need your help Sir to solve them
    thank you very much sir.

  39. Morning Sir,
    The problem of component borning has been solved by following this procedure.

    1. I connected the battery positive directely to the centre of transfo and then I used thin copper ware with switch to the positive input of the circuit board.
    2. The negative of the battery is also directely connected to the sourse of the two mosfet then I used another thin copper ware to the board.

    I think, this can save all the components in the board.

    Sir, still Iam exeriencing some problems.

    1. one of the mosfet is getting hot If i load the laptop or any higher wattages appilience like 100watts bulb.
    2. my multimeter is ok, but when connected it to the inverter in order to test the AC output volt it is reading wrongly and if connected to main AC its reading normal 220v or 219v.
    3. Still the inverter can not operate Fan.
    As usual, I need your help Sir to solve them

    thank you very much sir.

    • Aminu, which inverter circuit are you referring to?, is it the above inverter or the ready one faulty inverter which you are presently repairing?

      if it is the one which you are repairing, it would be difficult for me to judge and troubleshoot because I don't know what kind of circuit may be used in it and what stages may be involved…

  40. and what will be the effects on the same motor load if i was to directly connect it to the output of this inverter ???
    thanx for all ur help.

  41. so if the LC filter is added to the circut will i be able to run a 20 watt ac motor load without having the adverse effects on the pump ????

    • Salut Wileps,

      you simply have to use a transformer having an 120V rated secondary winding, rest everything can be as is

      il suffit d'utiliser un transformateur ayant une 120V évalué enroulement secondaire, du repos tout peut être aussi est

  42. Sir can you please suggest me what is wrong?

    1) If I connect a load with morethan 100watt the Mosfet are getting hot and even some of the component in the circuit are damaging, like the ware i used for making jumpers and some line in the viroboard.

    2) This new Inverter that I build (sinewave) cannot operate fan. I tried it with a table fan, and the fan is only emitting louder sound as if it is going to bust.

    In testing this sinewave circuit, I used:
    *12v 20A battery.
    *Transfomer removed from 500va UPS and,
    *IRF3205 mosfet.

    Thank you sir.

    • Aminu,

      The PCB is getting hot because the tracks or the jumpers are not able to bear the higher current level, you should use thicker wires and tracks for the PCB, and use a big heatsink for the mosfets.

      Adjust the PWM and see which PwM setting produces the most suitable results for the fan.

      actually the pot should be adjusted first for setting the output voltage of the trafo at the correct level, only after this it's recommended to connect the load

  43. Good Morning Sir,
    Am back with the result.

    As you asked me to do, so I did it.
    All the pots are working, because the LED's light is varying.
    Now, I changed the pot to 473. May be my moltimetre has fault that is why I cant see the changes in the AC volatge. But, even the bulbs I conneced did not show any change.

  44. Again Sir,

    With last and recent inverter I builded, I understand that, both cannot work well with transformer removed from old UPS.

    I tested with two transfo, one is 7.1-0-7.1 removed from 500va UPS and other has no detail but it was removed from 750va UPS non of them is able to operate PC, the transistor become hot instantly but they work on TV and bulbs.

    Finaly, I tried the other tranfo that I'am using which is rated 12-0-12 5A it operate PC normaly and light 26watt bulb at same time, so due to its low current (5A) it cannot operate the TV.

    Sir, I need your help on what best transfo should I use, that can operat many electronic apliencies. Because, Buying or winding new transfo may cost too much.

    Iam very grateful Sir,
    Thank for the helps.

    • Aminu, use 33uF, or 47uF, or any such high value capacitor in place of the 102 capacitors and connect lED in series with R7, R8…now check the LED illumination, it should flash alternately and the flashing should change on both the LEDs oppositely as the pot is moved….this will confirm your PWM section transistors are working or not.

      once this is confirmed positively you can again replace the capacitors with the 102, and if this time it doesn't work then it could be the 102 caps which can be deemed faulty.
      7V trafo is the correct one and will work optimally when the PWM is attached and adjusted correctly.

  45. Sir, You are great!!!

    Iam happy to informe you that, I have builded this Simple SineWave Inverter. Now, Its working normal and it provided me with full current.
    But, I did not used IC555 stage, I used the complete circuit above since it seems more familier to me.

    The only problem i got was in BC557/BC547 stage where one of the BC547 used is damaged and it allows the high volt to pass through it, Though based on your resent reply I have identified and solved problem.

    Now, Another Issue is on POT and some other component I used as result of their scarcity.

    1) I used 473 pot, then another new 473 and finaly I change to 503 pot still I cant see any difference in AC outpot when varying both the pots that i used.
    Anything wrong?

    2. I used 2A102j instead of 680pf.
    Can this affect the working of the pot or can it damage the applience operate with this inverter?

    Thank you very much Sir.

  46. Good Morning Sir,
    I have build this new circuit, all 3 parts are made seperataly in one board, but I did not test any.

    I want you to help me as usual with a trick on how to test the following stage.

    1. the IC555 stage without oscilloscop.

    2. BC557/BC547 stage.

    Thank you very much Sir, Iam very proud of you.

    • Hi Aminu,

      first check the circuit without the lower PWM stage

      assuming your 50Hz upper inverter works normally, and it should. initially keep the PWM link from the lower circuit T6 disconnected and check the voltage at the collector of T6 which should vary as the pot is varied, next confirm the frequency at this point and make sure it's 2 to 10 times higher than the frequency of the upper stage (50Hz), depending on the value of the capacitors C3/C4

  47. hi bro
    how are you ?
    can you please show a simple lc filter for the 220v side,i have 2.5uf ac cap
    how much is the l=?

  48. hello Mr. swagatam
    i have some doubts regarding this project.
    1)is this a square wave or a pure sine wave inverter.
    2)in the modified circuit there are 2(+ve) terminals but i cant see a -ve terminal,is there some thing wrong with the diagram or am i missing something which is obvious in epic proportions ??
    pls help.

    • Hello Akshay, The second variant is as good as a pure sine inverter, you might possibly need to put an LC filter at the output for enhancing the results, which could help make the output much like a pure sine wave.

      All the earth symbols in the diagram refer to the negative line and will need to be connected with the battery negative

  49. Hello Mr. Swagatam.
    I have couple of small questions regarding this project which might seem trivial,but i would be be grateful if u did .
    1)is this a sine wave or a square wave inverter ?
    2)In the modified circuit there are 2 (+ve)positive terminals and i dont see any negative terminal.is the diagram correct or m i missing something?
    much appreciated.

  50. Thank you very much Sir.
    I will try this updated version too.

    1. Sir, If I use IC555, is it necessary to do BC557/547 stage?
    2. In my old inverter builed from first circuit (SquareWave) I used 2A473j cap instead of 474j and the inverter is still working. Can this change course problem to the appliances Iam operating with it, Sir?

    Thank very much Sir.
    I will contact you very soon if am through with this version and the other one that convene ic555 pmw and transistive AMV.

    • Hi Aminu,

      If you are using PWM then the BJT will become necessary, to enable a better working of the mosfets.

      473 will give 10 times higher frequency than 474, that means your inverter would be running at 500 Hz which can be bad for the connected appliances which are specified to run at 50Hz or 60Hz.

      so make sure the frequency of the inverter is 50 Hz at 220V or 60Hz at 120V

  51. When I built this circuit in the past and I normally get the correct voltage but wrong frequency I realized you modified it, I'll try this updated version…. Could I use an arduino to generate pwm and send it to the diodes I'm wondering if the voltage would be too low because the arduino would be sending a 5v or less pwm Signal

    • the frequency has nothing to do with the configuration, it's simply due to the PWM freq interfering with the base 50 Hz frequency….if you analyze with a scope you would be able to get the correct figures.

      As for the modification a reassessment made me realize that actually the previous design too was safe and had no problems, earlier I thought may be the PWM would damage the BC557, then I realized that with no emitter current that would be impossible….so the new diagram is as good as the previous one….technical both are safe.

      5V would be fine as PWMs, no issues.

  52. Again Sir,
    1) This 680pf caps is not availabe in my area. Is there any changes in Caps and resistors of PMW?

    2) If I want use IC555 as PMW what is the value of following components?
    A) Resistors,
    B) Trimpot and
    C) Caps.

    Thank you Sir for your time and help.

  53. You are great Sir,
    Thank you very much… And I will do as you mentioned.

    But, Sir
    1) This 10E resistors seem to be identical with the 10R resistors used in the old circuit.
    Their colour are: Brown:Black:black:gold. Right?

    2) If I used 1.5watt for all resistors in the circuit what will happen?

    Thank you once again Sir. May God help you, protect you and reward you.

    • thank you Aminu, I have not removed the BC557 actually, just added a resistor at its base for preventive the damage.

      yes that's right, but the 10 ohm is not critical, it can be any resistor below 50 ohms.

      higher wattage resistors will not do any harm to the circuit just consume unnecessary space on the board.

  54. Sir, I think my problem is not in the building the above two AMV, but rather in the BC557/BC547.
    How can I check, If they are correctly configured?

    I cross checked the two circuit I made with two AMV and I learnt that, now only mosfet is instantely becoming hot. And while connecting the battery to the circuit there is little spark and the battery wire becoming hot too.

    Thank you Sir for all your help.

    • Aminu, You will have to configure them as shown in the diagram with correct lead connections, I also told you to measure the frequency, until you confirm the frequency at the various nodes, you cannot be sure about the results.

  55. Again, on the issue of venturing…
    I mean I want to build a very cheap, simple and brighter lamp that has less battery power consumption.

    For Example;
    A lamp with 3 to 6 bright LED type opperated with only two AA batteries.
    Because, here in the market, there are many kind of this lamp, but people complaining about the quality, the battery power consumption and it's ability to opperate only on 3 AA Batteries.

    So, I want, if available, any component to make changes.

  56. Ok Sir.
    I anticipated those bc557/bc547 to damage because they got smoke when the first problem happen.
    Now, I decided to give up this circuit and build new one.
    While, building new one, Sir can you please guide me on how to test any part I buid before proceding to the next stage. Thought, I mastered the first circuit but still I need some help.

    I also have multimeter but, I think I lack knowledge on how to use it properly.

    • Aminu, the BC/547/BC557 cannot go in smokes unless something's wrongly configured.

      anyway, in the new circuit first make sure the two AMV circuits upper and lower are oscillating correctly at the specified rates.

      you might be having a frequency range in your meter, use it to measure the frequency across the collector and ground of the transistors.

      the upper circuit must show around 50Hz…while the lower circuit should indicate some higher value depending on the pot adjustment.

  57. Yes Sir, I have rectified it. But, another problem, one bc557+bc547 part is damage. I discovered this after I removed the transfo and I left only a board with two mosfet, then I used LED across the two 10R resistors but, the LED did not light up. While if I connect the normal one with Positive battery power it light up, and if i repeat the procedure on other side with Nagative battery power, the LED will not ON.

    1. Sir, can this procedure work?

    2. And is it true that if the circuit is working the LED will light up? Because, I dont have another working circuit to confirm it, other than the above Square wave I made.

    Again, Sir do you have an idea on how to make a simlpe, cheap and few components brighter touch light operated on 2*AA batteries that last longer than usual?
    I'am asking you this because, I have recenty graduated and I don't what to stay for Government to give me job, that is why Iam blindly searching for an opportunity.
    I learnt that, our main problem in area I'm leaving is Light, that was what brought an Idea of inverter to my mind, even though there are many inverters in market that are very cost. And I have a little knowledge on electronics and I can devote my time on it freely and tirelessly.

    I have no words to express a gratitude.
    Am proud of you sir.
    Thank you very much for your time, help and king responses.

  58. Sir, I have discovered the problem.

    I learnt that, I placed the VR wrongly that is why Iam facing the problem.

    Now I changed new mosfets, and I disconnected the PWM section but the output AC voltage is very low.

    I can see VR has 3 leg, one in isolation part and other 2 in the same part. And I have four resistor's leg to connet them with it.
    So, Which VR leg should I connet to 1k and 27k resistors.

    Sir please help me as usual How to place this pot, because I tried it in any direction but it did not work.

    Thank you Sir!

    • Aminu, as i indicated before the trafo voltage rating should be lower than the battery voltage for enabling a correct voltage at the output, so make sure this rule is followed.

      the pot two end leads should be connected with R9/R10 while the center lead connects with the positive rail.

  59. Sir, as soon as I connected it to the battery, the mosfet is instantly become too much hot and some other component will start smoking. And I tried it without load as you suggested but the problem is remained unchange

    But, it worked by the time i build the circuit. This problem was started when I loaded a laptop.

    And, Sir is there any way to check the whether the circuit is fine or not before connecting it to the transformer.

    Thank you Sir.

    • Aminu, that will never happen if your circuit is oscillating correctly, or if the mosfets are correctly connected or are not faulty.

      disconnect the gates of the mosfets, and check the frequency at the collectors of the T1/T2, then at the base of the BC547/BC557, and finally at their emitter junctions….all should show an approximately 50Hz without the PWM connected.

      after connecting the pWM this must increase as per the PWM frequency.

  60. Probably Sir!!
    Sir, I dont know what is wrong with my inverter that i build with the 2nd circuit, its now damage 3 mosfet and sometimes its connection is burning untill i make jumper with copper.

    Pls, help me sir.

    And can I use the inverter I made from 1st circuit to on tv? Because, I try it now but the tv is ON and after some mints it OFF and instantly ON again.

    Thank you very much sir.

    • Aminu, that will be difficult to troubleshoot, you will have to find it yourself what might have gone wrong in your circuit. As you can see the concept is explained comprehensively in the above article, you will have to thoroughly understand how the two circuits are related and how these are supposed to interact, and how the pot needs to be set for an optimal response.

      you can check the output voltage without any load, and check whether the pot adjustment varies it or not…it should vary

  61. Great work sir,
    This circuit is very interesting, I used the first circut to charge and on a laptop and a bulb. this is amazing.
    The partlist i used are;
    1. 12-0-12v 5A transfo.
    2. Two FP50N06 mosfet
    3. The fist circuit orsillator and,
    4. 12v 20ah battey.
    With this, I on a laptop and a 10 watt bulb for 30 mint and the battey never empty.
    But, the transfo generate some sound and little heat and the two mosfet take less heat than transfo, So I dont know whats wrong.
    Am sure my Teacher Sir Swagatam will help me if there is problem.

    Thank you for all your help to us, and may god bless you and protect you.

    • thanks Aminu, such problems are difficult to judge….most possibly it could be due to a low quality transformer, because most companies try to save money on copper and iron and end up creating non-standard designs, and compromising on the quality of the trafos….it is difficult to get a really professionally designed trafo in the market.

  62. Thank you very much Sir, The problem is solved by changing the new pot. *So, can you please suggested me the mosfet to use for more wattage? Let say 500 watt.

    Again, I need your help on the above circuit.

    *If I use 12-0-12 5A transfo what wattage can it provide me with the first and the second circuit.

    *And can I use 12-0-12 transfo removed from 750va UPS with this circuit? If yes what wattage can it provide me?

    Thanks once again Sir, I realy like you much.

    • That's great Aminu, thanks for updating the info.

      you can try IRF3205 for achieving 500 watts however for this you will first need a transformer rated at 60 amps….yes a UPS 750va trafo will perhaps do the job…..and make sure the battery is also rated at 100 to 200AH minimum.

  63. Hello engineer, great work. pls can you make me a comprehensive article on using oscillator having IC SG3524 with IC 555/556 to generate a pure sine wave coupled with mosfet and center tap transformer, or how to perfectly smoothen modified sine wave using IC SG3524 with little or no distortions. Thanks sir

  64. Sir, I have completed building the 2nd circuit as you advise me to do inoder to opperate Fan, Tv, etc.
    So, I have a problem, that, If I connect a socket or an extansion that has an LED indicator the resistor of the LED is burning and produce smoke especial if I did not load.

    And, Is it possible to build 500 watt to 1000 watt using this process, If yes, please what component should I modefy to give me higher watt.

    Thank you very much for your help.
    May God see you through!

    pls help me

    • Aminu, please check the output voltage of your inverter, it could be too high, try reducing it to 220V by adjusting the shown PWM pot.

      you can upgrade the inverter simply by replacing the existing mosfets with higher rated mosfets……….. nothing else needs to be changed.

  65. Swagatam Sir, Thank you very much.
    I have compeleted my project right now, and my inverter is working perfectly.
    I test it with 100watt bulb and it fully on. and i try tv too. Almost all appiliences had been tested and work smoothly.
    My question here is if I can I generate more watt from the above project?
    let say, 500watt to above, what components should I modify?

    Thank you once again Sir.
    I like you very much!

    • That's great Aminu, I am glad to hear this.

      To increase power you will need to upgrade the transformer and the battery power to the specified levels.

      for example for achieving 500 watts the transformer will need to be rated at 24V/25amps, and the battery at 24V/200AH

  66. Sir, Iam Aminu who asked your help on simple 150watt inverter last week, and you refered me to this post, also you gave me an advice to try the second circuit of this post.
    So, since Iam new here, I started by builing the First Circuit and work perfectly, I Loaded Phone and Laptop cherger, I also operate Radio that used transformerless power supplier.

    My question here is;

    1. can I use 0.47uF/100V metallized in C3 and C4?

    2. Can I mix S8050 in T5 and T6 and PMS2222A in T1, T2 instead of BC547?

    Thank You very much for your Kind and Helpfull post.
    I like you very much.

  67. Dear Swagatam,
    On your 3kw pure sine wave inverter circuit diagram , I need to know the type of free wheeling diodes and wire gauge/ side of the transfomer both on primary and secondary winding.


    Bernard Tendengu

  68. how to design 5 level cascaded h-bridge multilevel inverter with 6 power MOSFET? please put the value of the component.i need the squarewave output waveform..

  69. OK I figured it out. Somehow its triggering the country firewall that was put in place to block the religously offensive material.
    Could I ask you to email this png to me please?
    Many thanks,

    • sorry, actually due to my busy schedule sending through email might not be possible, please check out the following link this might solve the issue.


    • Hi Swagatam,
      Thank you for posting the link.
      But I think this is the same link where your original pic is stored and something in this link triggers the country firewall.
      Would it be possible to upload this pic elsewhere like google drive or email if you have a free minute please?
      Many thanks for your help,

  70. Hello Swagatam,
    Thank you for this. I am trying to make such modification to my existing 1500watt modified sinewave inverter. But
    1. your second diagram is not showing for some reason.
    2. Could you please tell me if this same cct can be applied in my case for 1500 watt modified sinewave inverter?
    Thank you.

    • Hello Moen,

      yes it can be applied to any square wave inverter.

      you could probably try a 555 IC for generating the chopping PWMs, if the transistorized circuit looks difficult to optimize.

    • Thanks Swagatam,
      Would it be possible for you to look into why the modified cct is not visible? If possible could you upload it again please?

    • thank you sir! later they got stock on 547, my problem now is the AMV chopper or the lower circuit not working, if i connect the AMV circuit i got 0v output. i dont know how to test the circuit if working or not, but i used analog multi tester dc range, i connect the red test probe to +12 then black to collector, i got 8v, then 12 on end of diode. now i connect the black test probe to negative supply then red to base i got 2.5v, 3.5v on collector. now what is the problem on the circuit? what voltage supposed to be on end of diode? thank you

    • you will need a frequency meter for confirming the chopper working, or alternatively you can do the following:

      temporarily change C3/C4 with 33uF capacitors or any similar high value capacitor connect a red LED in series with emitter of any one the transistors, now check the LED response, if flickers and changes the rate of flickering then you assume the chopper circuit to be working fine.

      after this you can revert the circuit to its original form by replacing the configuration.

    • led light alternate left and right but when i replace the c3/c4 to original value its not working. so i tried to use 103 its work now but the xformer become noisy even adjusting the trimpot also the voltage current dropped. by the way boss thanks for your time to help us. i will buy frequency test and oscilloscope when i got enough money. sorry for my bad english, im hate english im not good in it.

    • very slight buzzing is fine…make sure the frequency from the upper astable is 50 Hz (for 220V output)…and the lower it could be around 500Hz…confirm these with a scope.

  71. Hello Mr swagatam my inverter which I am using for more than a year now I just on it today it showing me this (inverter out) and the output is blinking after some second it will show (protection) please I want you to help me with some ideas to solve this problem.thank you sir.

  72. Ok sir 1nf how many voltage because I put 102 but the voltage has dropped down to less than 120 and if I adjust the preset the voltage will drop to zero,sorry for my bad English,thank you.

  73. Good job Mr. swagatam I have finished making the first circuit and it works correctly,I am now working on the second one but I didn't get the capacitor 680pf please which number is equivalent to that, am really appreciate thank you sir.

  74. IRFP260N : Power MOSFET(Vdss=200V, Rds(on)=0.04ohm, Id=50A)
    And the transformer is 15v-0-15v
    240V 2000MA and I want my inverter to be 500watt if possible thank you sir.

    • 200V is unnecessarily too high…but nevertheless it will work

      multiply your tafo's amp with voltage….15 x 2 = 30watts…so the maximum capacity of your trafo is 30 watts…you cannot get 500 watt from it.

    • Basiru, please check the datasheet of the mosfets and tell me what's the amp and voltage specs of the mosfets, and what your inverter wattage is intended to be?

  75. Good morning sir I hope everything is ok with you please in this article the second diagram Is this all that is required of one to produce an inverter (complete diagram)? or is just a section of it? Thank you

    • Basiru, first make and confirm the working of the first circuit, if it works correctly then you can proceed with the second stage modification

  76. Hi mr swagatam
    As you know… I have inverter using sg 3525.. So should I use your second transistor circuit or should I use another sg 3525… And Connect only one pin like pin 11.
    Thanks .

    • Hi hisham,

      use the second circuit and connect the diode ends with the mosfet gates and check the response by adjusting the pot….

  77. Okkk sir. The meter is ok.. i did measured the pwm without the mosfet and i got the 60hz …. so maybe the problem could be the mosfets or the transf. ?

    • problem is not in the trafo or the mosfet….first measure the basic frequency without the PWM connections…and onec thew 60Hz is confirmed then you can connect the pwm back in position…PWM frequency is supposed to be 4 times more than the basic frequency (60Hz)

  78. Hello sir.. i have the same problem . I am using the sg3525. It show 60hrz for 5 secs then jump to 130 and after 10secs like 280hrz .

    • Hello Hector, your meter might be getting "rattled" with the PWM frequency and showing false readings….please check it using an oscilloscope….or first confirm the 60Hz without the PWM integration, once it's confirmed you can restore the PWM connection back in place.

  79. Q.
    Hello sir.
    I have the same problem with this inverter i am using the sg3525 .. the frecuency just staid at 60 hrz for 5 seconds after that jump to 135 and like 10 seconds later to 385 .. how can it staid at 60hrz.

    1. 1
    —————————– — ————————-
    0.7*112k+3( 1000 )*200nf. 78400+3000*0.0000002

    Thank 's.

    • It will work, but a 400v is not an appropriate match…

      preferably the voltage rating should be below 100V and the current above 30 amp

  80. Why does the square wave changes into sine wave at certain frequency?Can someone explain to me more briefly about it?

  81. Thank you, Sir, on this circuit
    I have a question can i use the second part only with my sg 3524 and irf064 mosfet inverter which I made ? it is already has a automatically voltage correction

  82. i build the above circuit : the transformer keeps making some noise .so i took the chopping circuit out but the 50hz oscillator together with driver cannot turn the 12 by 12 former. when i added the chopping circuit it was able to light a 100watts bulb at low voltage. what can i do to correct this. noise

    • the noise can be reduced by increasing the values of C3/C4, however removing the chopping circuit should in fact make the inverter more powerful,,,there's something not correct with your 50Hz circuit, check it for any faults.

  83. I disconnected the lower half and these are my results from testing
    I am getting between 32v and 44v rms

    Average voltage is fluctuating between -27v to +44v

    Voltage peak to peak is showing 444v and sometimes 81v

    On my multimeter i am getting 126v

    Frequency on my meter stays at 69hz then jumps to 138hz then to 289hz in a dpace of 10 seconds

    On the scope i borrows the frequency show 4.58kc

    And duty cycle shows 99 and 100%

    • all these are weird results and will never happen under normal conditions…it seems either your measuring devices are faulty, circuit is wrongly connected or the components are faulty.

  84. I started from scratch again with this circuit and with a 9v center tap transformer I got 94v but I realized that the transformer was squeaking so i tested the frequency and I got 4khz, the only part i used different from whats in the schematic is that I used a 50k preset instead of 47k, so what could cause the frequency to be so high and my voltage doesnt go any higher when I adjust the preset the voltage goes down and I am trying to get 110v

    • isolate the two stages and confirm the outputs separately….once confirmed you can integrate them for the final results.

      the lower circuit is designed to produce high frequency…the upper one for producing around 50 Hz.

  85. I did im getting 75v out if i use to 2 legs that should give me 220v im getting 120v i connected a normal house fan to it and it didnt even spin a little

    • remove R5/R6 and connect the gates directly with the collectors…also measure the current by connecting an ammeter (10amp) in series with the battery.
      check the response…if still it does not yield the required results you can assume either the battery, fets or the trafo may be not good or incorrectly connected.

  86. I used 2 irfz44n and one of the transformers were 12v 5amp and one was a microwave transformer that i got wrapped over they said its about 500watts and i tried a 9v 3amp transformer

  87. I used a 12-0-12, 5amp and also same voltage 10 amp and i tried a 9-0-9 3amp and and i got similar voltage the 9 volt brought it up by about 10volts but it couldn't turn on any load

    • 12-0-12/5amp will support not more than 40 watts load and 9-0-9/3amp not more than 25 watts….if at all these are accurately rated otherwise the output could be even less

  88. ok I finished this circuit and from the 110v section of the transformer im getting 75v and the 220v section im getting 120v, thats from a 12-0-12 and I got 85v and 140v from a 9–0-9 transformer… the battery i used was a 12v 65ah car battery and battery voltage stayed at 12.6 volts while testing and fets were warm not burning up… so what could be the prob plus I am not getting much power from it because I tried connecting a a contactor and it didnt energize the coil.

    • yes it will…… make sure you add a 0.47uF/400V capacitor across the output terminals of the transformer for cancelling bad frequencies.

  89. Hello sir,
    Santanu again. You said that the amv chopper circuit produces high frequency <50hz. So wont it cause any problem to run 50hz appliances in it?
    and if i add an existing square wave inverter made of 555 and irf540 and add it to the amv chopper will it give output waveform shown by you? Please reply soon.

  90. I have the diode positioned accross the drain and source like in the previous build without the sine wave, do I have to shift them to add the sinewave portion?

    and there is no dot on the line above the vr1 so just asking is it connected it the line above it?

    • I did not understand your question? which thread are you answering to? please comment under the same thread so that I can follow it properly

  91. Hi Swagatam

    Can i connect the chopper circuit ( only ) to a ready made modified sine wave inverter ?
    if yes how much watts can it afford ? thanks

    • Hi Ahmed, if the ready made inverter is already a sine wave modified then you wouldn't require the chopper circuit, it's recommended only if the inverter is square wave type.

    • The problem is the modified sine wave inverter i have im using it to power an lcd tv, the inverter is 600watts , and the tv is a small one (19 inch ) it works well unless a strange sound coming from the tv power section ..like ( zzzzzz),, i used a friends inverter it was 300watts pure sine wave,, and the (zzzz) was gone,, i thought using the chopper circuit will turn it into pure to fix the problem

    • I think you should try using a filter circuit first, that would most probably solve the buzzing problem.

      Try incorporating a the following network directly across the output of the inverter


      Initially try the 1uF capacitor alone…. if the problem still persists you can go ahead with the remaining parts in the network.

  92. I used an 8-0-8v transformer, I used a 12v battery and I get 350v AC, bt wen I connect the diode from the 2nd circuit(PWM), the voltage drops to zero, I also turn the 47k pot trim but iget no results.

    • change the 47k pot with a higher value pot, example you can try a 220k, 470k or even 1M pot, this will allow you to select from a wide range of PWMs.

      adjust it to get around 220V at the output

    • you will need to adjust VR1 correctly for getting optimum results and the trafo voltage rating shpuld be selected as 30% to 40% less than the batt voltage.

  93. For voltage correction, can we connect the collector leg in the link below to the output of C4 to the diode? Will it work?


    • Am afraid this won't work, because the circuit diagram of the voltage correction you have doesn't have a transformer, hence the voltage is just rectified to abt 200VDC which could damage the mosfet which accepts 55v. I think we should use a smaller TRF to step down to b safe.

    • the transistor shown in the voltage correction diagram will ground the inverter shutdown pin to which its connected for implementing the regulation, it will not supply any high voltage to the circuit with which is connected…

  94. I am not using a 50hz IC, I am just using a 50hz square wave oscillator using transistors and resistors as shown in the post above. Would it also be fine too to power the oscillator with 5,6,7 or even 12volts regualtor for a stable voltage.

    • Since the gate voltage is usually the half of the supply voltage(12v), therefore the PWM peak voltage should be 6v. How can I ensure that I set the peak PWM to 6. What's the configuration

    • mosfet gate voltage (peak) will be always equal to the IC supply voltage which is being used for driving it. If the IC supply is 12V, the gate voltage will be also around 12V peak.

    • Hello ifeanyi, the 555 output positive PWMs voltage should be equal to the mosfet 50Hz voltage, otherwise the PWM may not produce the correct effect. If the 50Hz IC is also driven with 5V then it would be fine.

  95. Hello swagatam, according to the design in this post and the one in the post in the link below. Which of the PWM diodes is correctly connected. Or it doesn't really matter how we connect it? 4.bp.blogspot.com/-4pFtMm0wuPQ/ULHioWwpZlI/AAAAAAAABnE/Q2UjJoTsFBU/s1600/Modified+sine+wave+inverter.png

    • Hello Ifeanyi, both are correct, the diode polarities are opposite because in the above article the driver devices are N-type while in this link it's P-type

  96. Hello swagatam…. Please can u modify dis circuit to it regulates outputs to a steady voltage even on load like the one you posted in dis image. 4.bp.blogspot.com/-5GDTaart2mw/UmYX6r5TyzI/AAAAAAAAFiI/il_1gPepQVQ/s1600/inverter+output+voltage+correction+circuit.png

  97. I found an obscure article about how a Russian took a 330nF Capacitor, went across his 220v output MSW inverter signal, and was able to 'filter' the resultant into a 'near replica' of a PSW form. I don't have a scope to test this myself, have you ever tried to 'end filter' a MSW and scope it to see if you can 'filter' the wave a bit for a 'bubba sculpting session'? I may have misread him, that 330nF seemed awful small to work on that voltage, but you never know (probably was mu, not nano).

  98. Good day!

    I would be able to help with a design using ordinary discrete components, as already i have presented plenty of such designs in this blog.

  99. Not more than 150 watts, at this much load the battery will last for 5 to 6 hours. You can use higher loads also but the battery would drain quickly.

  100. Dear Sir Swagatam,
    I am a fan of your blog and I've been inspired by your work.. for that i thank you very much.. how can i use ic 555 to joint with this circuit "sine wave inverter" to produce 220v at 60hz.. can you provide me a link… thank you very much sir.. and sorry for my bad english and where is D1 & D2 connected?
    sorry i am new to electronics..


    • The output will be modified sine wave not pure sine, but should be OK for PCs since all these gadgets have an AC to DC converters, so won't make any difference

    • if the two circuts are used … why the out put will be modified it should be converted to pure sine wave…am i right ?

    • check the output 220V level while you adjust VR1, it will change in response to VR1, adjust until the output settles to the required level.

  101. Hello Sadi,

    Change the position of VR1, use two of them and connect in series with R9 and R10.

    Adjust them carefully to get the required results

  102. Helo Sadi,

    Yes you can employ the concept for modifying your existing square wave inverter.

    RMS value would be simply the voltage that's specified at the output of your inverter without any load.

    If it's 230V then adjust the preset until the output comes down to 230V….it's now set.

  103. hellow swagatam, incase I add two more mosfet and connect them in parallel, in that case we will be having two mosfet in each side, Now how Will I Connect the chopper circuit on the mosfet? I have connected the gates with 1k resistor and sources with a thin wire of o.2 ohms. The inverter is working perfectly but i have a problem in connecting the choper circuit, please sir help

    • Hello hasan,

      Don't connect the gate resistor common ends directly to the collector of T1/T2 rather connect them via another 1K resistor, now you can join the PWM diodes at the junction of these two 1K resistors,

      Use 470 ohms instead of 1K that will be better.

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