PWM inverter circuit

admin November 10, 2011 203 Comments

250W PWM inverter circuit SG3524.

A 250W PWM inverter circuit built around IC SG3524 is shown here. SG3524 is an integrated switching regulator circuit that has all essential circuitry required for making a switching regulator in single ended or push-pull mode. The built in circuitries inside the SG3524 include pulse width modulator, oscillator, voltage reference, error amplifier, overload protection circuit, output drivers etc. SG3524 forms the heart of this PWM inverter circuit which can correct its output voltage against the variations in the output load. In a non PWM inverter the change in output load directly affects the output voltage (when output load increases output voltage decreases and vice versa), but in a PWM inverter the output voltage remains constant over a range of output load.

Circuit diagram of 250W PWM inverter.

250W PWM inverter circuit

PWM inverter circuit

About the circuit.

Resistor R2 and capacitor C1 sets the frequency of the ICs internal oscillator. Preset R1 can be used for fine tuning of the oscillator frequency. Pin 14 and pin 11 are the emitter terminals of the internal driver transistor of the IC. The collector terminals of the driver transistors (pin 13 and 12) are tied together and connected to the +8V rail (output of the 7808). Two 50Hz pulse trains which are 180 degree out of phase are available at pin 14 and 15 of the IC. These are the signals which drive the subsequent transistor stages. When signal at pin 14 is high, transistor Q2 is switched on which in turn makes transistor Q4, Q5, Q6 ON are current flows from the +12V source (battery) connected at point a (marked with label a) through the upper half of the transformer (T1) primary and sinks to ground through the transistors Q4, Q5 and Q6. As a result a voltage is induced in the transformer secondary (due to electromagnetic induction) and this voltage contributes to the upper half cycle of the 220V output waveform. During this period pin 11 will be low and its succeeding stages will be inactive. When 11 of the IC pin goes high Q3 gets switched ON and as result Q7, Q8 and Q9 will be also switched ON. Current flows from the +12V source (marked with label a) through the lower half of the transformer primary and sinks to the ground through transistors Q7, Q8, Q9 and the resultant voltage induced at the T2 secondary contributes to the lower half cycle of the 220V output wave form.

The output voltage regulation section of the inverter circuit works as follows. The inverter output (output of T2) is tapped from point’s labelled b, c and supplied to the primary of the transformer T2. The transformer T2 steps down this high voltage , bridge D5 rectifies it and this voltage ( will be proportional to the inverter’s output voltage) is supplied to the pin1 (inverting input of the internal error amplifier of the IC) through R8, R9, R16 and this voltage is compared with the internal reference voltage. This error voltage will be proportional to the variation of the output voltage from the desired value and the IC adjusts the duty cycle of the drive signals ( at pin 14 and 12) in order to bring back the output voltage to the desired value. Preset R9 can be used for adjusting the inverters output voltage as it directly controls the amount of voltage fed back from the inverter output to the error amplifier section.

IC2 and its associated components produce an 8V supply from the 12V source for powering the IC and its related circuitries. Diodes D3 and D4 are freewheeling diodes which protect the driver stage transistors from voltage spikes which are produced when the transformer (T2) primaries are switched. R14 and R15 limit the base current of Q4 and Q7 respectively. R12 and R13 are pulldown resistors for Q4 and Q7 which prevents their accidental switch ON. C10 and C11 are meant for bypassing noise from the inverter output. C8 is a filter capacitor for the voltage regulator IC 7808. R11 limits limits the current through the indicator LED D2.


  • Mount the SG3524 on a holder.
  • All capacitors other than C10 and C11 must be rated at least 15V.
  • Preset R9 can be used for adjusting the inverter’s output voltage.
  • Preset R1 can be used for adjusting the inverter’s operating frequency.
  • Transistors in the driver stage require heatsink.
  • T2 is a 220V primary, 12V secondary, 1A transformer.
  • T1 is a 12-0-12 V primary, 220V secondary, 300VA transformer.
  • Driver transistors must be isolated from the heatsink using mica sheets. Mounting kits for these transistors are easily available in the market.
  • An optional finned aluminium heatsink can be attached to the 7808.
  • If 1A bridge is not available, make one using four 1N4007 diodes.
  • Aravind
    July 26, 2015

    hello sir.pls tell can I replace power trans by mosfet
    and also pls tell calculation of battery rating and transformer capacity rating

  • Mahesh Chitti
    March 27, 2015

    I have design the above circuit that is 250w pwm inverter,only i have replaced the transistor by mosfet but i am not getting the desired output that is 220v instead 214v,Even by adjusting the preset so please kindly help me to get down of this issue.

    • Armstrong Alhassan Buba
      August 18, 2015

      your preset VR is not responding because the collector of your transistor is not connected to GND. Please do that and see if it will work

  • March 9, 2015

    i want to purchase this voltage converter 250W output and 12W input so kindly request you to send me your dealer contact details in pune , Maharashtra

  • dhk
    February 25, 2015

    From where i can get transistor 2N6227 in india? please tell me that place or provide any link for that camponent.

    • Rafi
      July 1, 2015

      You can use 2N3773 OR 2N3055 instant of 2n6227.
      I hope it is help you.

  • Donald
    February 17, 2015

    Thanks 4 d schematics. pls to construct a 5KVA inverter, what adjustments should I make in this circuit?

  • essien
    January 24, 2015

    Sir can I use 12v 100amps battery for this circuit

    December 1, 2014

    I am presently constructing an inverter using your circuit diagram. Please, I want you to discripe how I can use voltmeter to measure the output of oscillator at pin11 and pin14 of IC SG3524.

      December 4, 2014

      Please, why do you not respond to my requet posted on 1/12/2014. Treat please.

      December 4, 2014

      Please, why do you not respond to my requets posted on 7/11/2014 and 1/12/2014. Treat please.

    • Rafi
      July 1, 2015

      You should use frequency enable DMM meter . normal volt meter can not measure the isolation.
      Thank you

    • Stanley
      July 5, 2015

      You can test the frequency of th output using a multimeter that can read frequency. Fluke has lots of product. you read from the terminals of pin 11 and 14

    November 7, 2014


    • seetharaman
      December 7, 2014

      sorry for the delay in reply, the transister collector should be connected to ground then it will act as an integrater for soft start. only wave form can be checked with an oscilloscope, multimeter cannot measure it. you can use a frequency meter to find the frequency available at those pins, should be 50 Hz.

  • October 12, 2014

    I think this is very useful as the circuit is well explained except this function of BC327. Thank you for that.

  • Pankaj
    August 29, 2014

    Someone help me ,i made it but the o\p of sg3524 is zero.whats the prob.

    August 23, 2014


  • okpala michael
    August 9, 2014

    sir pls i need ur help

  • okpala michael
    August 9, 2014

    sir what is the function of BC327 there in the circuit

  • August 7, 2014

    I made this circuit using IRF3205 instead of the three driving transistors. I didn’t test it on loads yet, but when working as OC I had 210 volts to 70 volts output range by varying R9 between 0-5K ohms.

  • okpala michael
    July 29, 2014

    sir please i don’t understand the function of BC327 there in the ckt

  • okpala michael
    July 28, 2014

    sir please answer comments

  • vasudev
    July 28, 2014

    hi setharaman why have you stopped answering the comments

  • Treasure
    July 26, 2014

    Please sir, must the output at pin 14 and 11 be the same with that of the driver’s unit? Because the output at pin 14 and 11 reads 3.87 while the respective driver’s reads 4.07.

  • Yusuf Dauda
    July 22, 2014

    Pleae sir, can I convrt the 250Watt inverter to 1000Watt or more by just inceasing number of driver transistors or mosfets and the suitable transformer T2 without alter the oscilator and the feedback circuits, thanks.

  • vasudev
    July 17, 2014

    hi setharaman are you sure that this inverter works properly ?,can i use 9-0v 750ma transformer in place of t2

  • okpala michael
    July 13, 2014

    sir i need a pure sine wave inverter ckt

  • okpala michael
    July 13, 2014

    sir i don’t understand the function of BC327 there in the ckt.

  • okpala michael
    July 13, 2014

    I have build it but the output voltage changes when increasing load. what must be the problem.

    • emejakpor emmanuel
      October 1, 2014

      Adjust the 2.2k pot, to set the pulse width modulation, so that even when u increase load, the voltage will not drop below 220v, provided u are not overloading. Overloading wil put ur mosfet to stress and damage, since ur mosfet wil do more work. This circuit doesnt contain battery low shut down.

  • vasudev
    July 6, 2014

    hi i used irfz44 mosfet ,it works well

  • vasudev
    July 4, 2014

    can i use mosfets to drive the transformer ,because transistors are quit slow and have internal resistance compared to mosfets

    • seetharaman
      July 4, 2014

      2N6277 is a good switching transistor with very low switch on resistance. Bipolar transistors are much faster than MOSFETs of course their switch on resistance is quite lower in the order of few milli ohms. You may try mosfet in place of 2N3055 & 2N6277 combination retaining BC337. As I have not tried I can only suggest. You may try and give us a feedback on that.

  • vasudev
    July 2, 2014

    can i use 250mA transformer (t2)instead of 1a transformer

  • vasudev
    June 30, 2014

    hi setharaman what is the advantage of pwm inverter over cd4047 inverter

    • seetharaman
      June 30, 2014

      Output voltage will be constant with varying load, due to voltage feedback. It will not be constant in cd4047 circuit.

  • omisore sola
    June 22, 2014

    please can i know the voltages of this capacitor. After i ddi the circuit my output from the oscillator is giving me 3.5v on pin 14 and 11. What do i do

  • June 17, 2014

    Ehem…hm.. I think this inverter will not work unless you change the pin out 7808 as shown in diagram V+in(pin1),V-ground(pin2),V+out(pin3) 😀 peace 🙂 i sorry for those who burst their voltage regulator ic 7808.. Reyo here 🙂

    • Seetharaman
      June 17, 2014

      Constructors who have basic knowledge about voltage regulators might not have made the mistake and would have completed the project successfully. Thank you for pointing the mistake.

  • LordB1
    June 7, 2014

    sir, I unknowingly bought IRF540 when I was supposed to get IRFP250 but when I tried to check the equivalent they have just little difference.. so can I use it in place of the Q7,8?? thanks!

    • Seetharaman
      June 8, 2014

      Yes both MOSFETs are almost have the same parameters can be substituted.

  • LordB1
    June 3, 2014

    hi! am so troublesome which I know of, please wanna know if my calculation is correct?? if I say I want an inverter of 3750w and I want it operate for 24hrs round clock, taking note of the the supply voltage to be 60v(5 batteries in series) the battery amp should be 60V30AH??

    • Seetharaman
      June 4, 2014

      Inverter of 3750 watts say power factor and the inverter loss etc etc say the efficiency is just 65% Then it should be 3750 / 0.65 VA rating in the primary of the transformer. Approx 5800 VA. So you want an operation for 24 hrs. 5800 X 24 = 139200 VAH. with a 60 volt battery the AH requirement will be 139200 / 60 = 2320AH battery. With your 60Volt 30AH battery it will work for a maximum of 20 minutes. Not even for 24 minutes how could be for 24hrs ???!!!

      • LordB1
        June 5, 2014

        Sir, I have requested for a transformer with 750va which is the T2(12-012)V now what about the T1?? Should it be specially made or we can get the normal type at the market??

        • Seetharaman
          June 6, 2014

          T1 is a standard 12-0-12 volt 1 amp transformer (12 VA rating)
          For a 750VA transformer (500 watts load approx)you can calculate from the above calculations. approximately 12 volts 75AH batteries 4 nos you have to use in series.

          • LordB1
            June 6, 2014

            Okay, thanks! but one question, a non-inverter transformer is far different from an inverter transformer??

  • June 2, 2014

    Inverter and solar charger technology transfer

  • LordB1
    June 1, 2014

    sorry to bother you, I forgot to include in the text what cables or wires to implore in the connection?? though I aware of the fact that I do need jumper wires but are there other parts where I might need wires more thicker than jumper wires??

    • Seetharaman
      June 2, 2014

      All wires connecting transformer primary to positive supply and the wires connecting to transistors Q4 to Q9 should be 4sq mm or better and should be as short as possible.

  • LordB1
    May 31, 2014

    what part of the stages requires a heat sink??

  • Sunday
    March 23, 2014

    In pwm inverter, does battery variation affect o/p voltage? that is will the output reduce as battery voltage reduces?

    • LordB1
      June 1, 2014

      hi! with little I understand, that’s an advanced circuit configuration using PWM.. if the circuit is using the required specs it will have no effect with the battery, the battery will discharge at a steady rate depending on the load and the load output remains same irrespective of the battery discharging….

  • gbenga
    March 20, 2014

    hello, i like this circuit and will make sure its constructed. i have few questions to ask.
    1. will the output be reducing as battery voltage reduces?
    2. can i uses 8-0-8 , 230v transformer? if yes what would be my output? thanks!

  • Anthony56
    February 19, 2014

    Need your urgent help & advise for a Solution the following problem encountered as listed below and What are the possible Root Causes & Reasons of my problem encountered here ??

    1)Can not obtain Output Voltage of 230V AC & Output Current of 2A AC by using 500VA(500Watts) Transformer(T2).
    I hv completed building the circuit accordingly but obtained maximum output voltage only 83V AC at Secondary Winding of T2)& Maximum Output Current 0.06A only using load 28W 230VAC Bulb Or 100W 230V AC Bulb, Observation Bulb can light up dimly only. The Input Current of 8A ( Ammeter Reading ) 12V at Primary Winding of Transformer T2. The Transformer T2 used here that I bought from the shop is 500VA(500Watts) 12V/230V AC. Also I used Car Battery Lead-Acid Type 12VDC,60AMax.
    From the pin 14 of SG3524 using Q2(BC337),Q4 TIP122,2N3055,4pcs 2N3773 replaced 2N6277 that is Not available from the shop and adding one Small Resistor of 0.1 Ohms in series with Primary Winding Of Transformer T2. The Load 28W 230V AC Bulb Or 100W 230 AC Bulb can not lighted up without added this 0.1 Ohms Series Resistor.Not Sure Why need to add this 0.1 Ohms Resistor, pls share your thought & advise urgently.
    Wherelse from your project Original Circuit do not require this additional 0.1 Ohms Resistor to Transformer T2 that can even produce Output Voltage 230V AC from Transformer T2 per your circuit description & explaination. Do I missed something here ?
    From Pin 11 ( SG3524 ) using Q3 (BC337), Q7 (TIP122), 2N3055, 4 pcs 2N3773 replaced 2N6277 that is Not Available from the shop.
    I did obtain 50Hz Output from Pin 14 & Pin 11 of SG3524.
    Hope to hear from you all soonest possible & thks in advance.

  • Ajinkya
    February 15, 2014

    sir, I want 10KW Solar inverter circuit. If possible please send me as early as possible.

  • abankwa
    February 10, 2014

    i need sg3524 to buy im in ghana obuasi

  • abankwa
    February 10, 2014

    i need sg3524 to buy im ghana obuasi

  • February 6, 2014

    Dear Sir

    i made that inverter it produces a 220v well with neon lamp but when i connect it to a computer or LCD tv the output became not stable the frequency became not stable decrases and increases..
    any ideas sir


  • January 18, 2014

    My inverter is only showing the green light but no output.what may be the cause?

    • Seetharaman
      January 19, 2014

      Have you connected you DC supply to Transformer T2 primary center tap. Without this connection the final output transistors will not get supply to function.

      • January 21, 2014

        That inverter was working and it just stopped whilst working.obviously there is a part damaaged and i dont know what is it

      • Praveen
        February 1, 2014

        Hello Sir,

        Sir i need to build a PWM inverter with output voltage control(50v-230v). Please mail me a proper circuit if u have.

        Thank you.

        • September 4, 2014

          Hello Sir,

          Sir i need to build a PWM inverter with output voltage control(50v-230v). Please mail me a proper circuit if u have.

          Thank you.

  • Pradip Debnath
    January 10, 2014

    Thanks for the schematic
    can you send me this sch file, Plz.

  • Miroslav
    January 6, 2014

    thanks for the schematic. I will try to built it. But I would like to ask you, do you somehow have some osciloscop plots of the output waveform? Or Pin11/pin14 IC? Thank you again for the schematic!

  • January 4, 2014

    This circuit can be was transformed to sinewave by me . by redesigning the oscillator circuit .adding three more IC chips after the Sg3524 pulses to produce sinewave at the output .If u need the circuit and a transformerless 3-stage automatic charger 12v 15amps .

    • Johann
      July 28, 2014

      Hi Simeon, thank you! Please send the circuit.

  • tommy
    December 1, 2013

    what might be going wrong that makes the voltage drop drastically If the fan comes on an I connect another load to it. it makes the television I to connect struggle to stay on. it keeps on tripping on and off.pls I really need ur help. also am I free to connect output from pin 11&14 directly to my power circuit or must I pass it through Q2 & Q3 & R12 & R13 first

    • Seetharaman
      December 5, 2013

      Q2 and Q3 are buffers not to load the IC. Check the quality of the inverter transformer and battery capacity. T2 primary voltage rating should be 11-0-11 or even 10.8-0-10.8 for a better transfer from 12 volt battery. For 5 hrs backup operation at rated load you require a 140AH 12 volt battery with a good charger.

    • February 6, 2014

      yah me too having this problem when conect a lcd tv or computer it keebs go on and off and the fan run very slowley but when i connect only fluresnt light or bulb it goes very well what could make that???

  • Oyedele.
    November 27, 2013

    you should have half the voltage in pin13& 12 as your oscillation output………..but this means with ref to ground…….check this……connect your test lead to pin 11&14 in ac mode… your voltage should be equal to voltage @ pin12/13,,,,,,,,,

  • tommy
    November 12, 2013

    is the circuit alright if I still discover a DC voltage of about 0.03

  • tommy
    November 12, 2013

    pls what might be going wrong with the circuit if I discover 11v from pin 11 and 14

  • oyinz
    October 4, 2013

    pls can i use a vero board for this circuit and i got a value of 01j 400v for the 0.1uf capacitor and i need a mosfet connection circuit for 1500watt inverter

  • Olu-Samuel
    September 28, 2013

    I want to commend you on this good job, please keep it up however I have these following observations and questions:

    1. T1 is not shown in the diagram.
    2. Note: Is this statement correct : pin 14 and 12 or 11? (This
    error voltage will be proportional to the variation of the output
    voltage from the desired value and the IC adjusts the duty cycle of
    the drive signals ( at pin 14 and 12) in order to bring back the
    output voltage to the desired value.)
    3. If I want to add more transistors to archieve for example 1000W, which transistors would be added and doe it require more base resistors too?
    4. Kindly expanciate this please: If a transformer is rated as 5000W, 220V by 12-0-12V, how can I determine its o/p current using DMM or any other devise?
    Expecting your response please, thank you.

  • oyinz
    September 22, 2013

    can i use a vero board for this circiut and got 3k vr can i use it to replace 2.2k vr

  • oyinz
    September 22, 2013

    pls here is my question how can i test the driver circuit after completing it so to know if it working or not

  • September 9, 2013

    Nice circuit..let me ask can i use Mosfet transistor as driver for the replacement Of 3055?

  • Kibuuka andrew
    September 7, 2013

    Hello there,what are the most available equivalent of 2n6277

  • ayobami
    September 1, 2013

    thanks for the good work. it is very inspiring. please can you send me the explanation about the whole circuit. i have decided to use it as part of my final year project and i need elaborate explanation about the function of each components in the circuit. although i know some but not all. for anyone that can help me, my email is . thanks all. i will expect response from anybody cos i need it urgently.

    • jojo
      September 5, 2013

      Hello Ayabami, We have given a detailed description of the circuit and list of components. Let me know if you have any other doubts.

  • Oyinz
    August 17, 2013

    Can anyone help me repair my digital multimeter it R6 burn out and it value number is burn too i dont know the value to use to replace pls give me reply on my email or post it pls. I cant read any component anymore pls help me

  • Oyinz
    August 17, 2013

    Pls sir am happy for this circuit i had a question that can i still remove the 2n3055 transistor if i had no volt drop sir pls i am waiting

  • Oyinz
    August 17, 2013

    Pls sir am happy for this circuit i had a question that how would i calculate the turns, ratio and diameter of a transformer

  • Oyinz
    August 15, 2013

    Pls any one with responde

  • Oyinz
    August 14, 2013

    What is a optocoupler sir

    • seetharaman
      August 17, 2013

      Hi Oyinz instead of using wire for transmitting data from one system to other, you use optics to do the job so that you get isolation between sender and receiver.
      Yes you can use more transistors in parallel to achieve higher power output.
      Where ever it is written +12 connect them together to +12 of the battery. the connection shown as earth should connected together and in turn should be connected to -ve of the 12 volt battery.

  • Oyinz
    August 14, 2013

    As you said nickk in instructable to increase the wattage u will add pair of Q7 and Q8 to increase it does it work for mosfet too bcause i need a 1500watt inver ter

  • Oyinz
    August 14, 2013

    Pls i am a primary student in electronics pls where will i connect the battery negative charge to on the circuit pls and so there are 2 +12v dc written there which one will have the positive of the battery

  • Joshua
    August 13, 2013

    Thanks alot sir, i really learned alot.
    My question is this, what formula do you use for calculating the transformer number of turns and the gauge to use, and even the size of the core, and lamination that can be used, thanks alot, i will be greateful if you will mail me back. Thanks alot more grace to your effort.

  • Sreejith
    July 11, 2013

    I trying to assembling this one dout
    1.where i will connect on 12- in this circuit..??

  • Neeraj verma..
    May 11, 2013

    Mujhe ye janna hai k is circuit me 2 transformer kyon use kiye gaye hain ?

  • 2n6277 transister
    April 10, 2013

    plz send me 2n6277 transister available shop address in india.

  • 2n6277 transister
    April 10, 2013

    2N6277 transister availble shop address send me plz in bangalore, india.

  • Oyedele
    April 2, 2013

    Let’s all go for mosfet….mosfet can perform the work excellently….I use mosfet mine is still working…with mosfet we can eliminates Q4 to Q6 and so on..connect the 100ohms resistor directly to the gate. The voltage present at the 100ohms resistor is enough to turn it on….using this mosfet little heat sink is enough…..bcz mosfet emits little heat………for more on how to do this text or call me on …08038252105….im available to assist…..

  • Oyedele
    April 2, 2013

    Hello…this circuit is a great one…I modified mine by replacing those transistor 2n3055 and 2n6277 with 2 mosfet in parallel irf3205 this mosfet has max of 10v gate to source voltage and is capable of handling 100A see their datasheet.I connect the output from the bc337 directly to the gate of the mosfet..I also remove those two diodes….08038252105

  • Sunday Chinedu
    March 18, 2013

    In this circuit, I observed that therre’s no battery. the circuits takes a rfaction of the output, rectifies it and uses it as the input DC. Does that mean that once a battery triggers it ON, we can remove battery?

    • Seetharaman
      March 29, 2013

      Hi Chinedu Without battery this cannot work. The battery is connected between inverter output transformer centre point which is written as +12Volt DC and negative of the battery to common ground. The inverter output voltage level is taken as feed back information to maintain the output voltage constant with variable load, within its capacity.

      • rakesh
        April 10, 2013

        plz send 2n6277 transister available shop address.

      • Oyinz
        August 14, 2013

        Pls where can i get the component for this inverter in nigeria at offa kwara state

      • Oyinz
        August 14, 2013

        But there are 2 +12v dc in this circuit and so many common ground

  • madan
    March 4, 2013

    Sir did ic sg3524 is available in india sir please replay me

    • Seetharaman
      March 29, 2013

      Hi Madan it is freely available in India around INR25/-.

  • Adelusi
    March 2, 2013

    Thank for this circult, please sir kindly tell me perhaps this is square waves or sine wave.
    Can i connect the GNDS to line between BC327 and pin 9 of the IC ? At oscilator side there are GND at 2N6277@emitter
    which line can this be connected. Thank. Please reply to my mail.

  • Gowthaman
    February 25, 2013

    Please help me sir i get output voltages very low that is only 50v and transformer & 2n6277 transister is more heat

  • January 4, 2013

    i am happy to have this diagram

    • peter
      January 13, 2014

      What is the purposely thing you won’t 2 do with the transformer.

  • December 15, 2012

    hello nickk i thank you for posting this schematic i have tried to make it and it works well but i need a shematic which can supply it with 12v only by holding a button one time and when we hold again on the same button the inverter shuts down.please help me

  • eng anas
    December 8, 2012

    Q1 I don’t understand work of it please help me

  • jermy
    December 3, 2012

    plz can some 1 tall me the number to turns and wire gauge of inverter transfomer for 1500 watts both primary and secondary winding

  • November 30, 2012

    pls can sombody help me with this circuit at the driver trasistors(bc337) can iuse it to dive two irf250n

  • sujan
    September 24, 2012

    hi.. i dint understand the use of another 220v primary 12v secondary 1 amp transformer.
    for what purpose is it used for??

  • DAMS
    September 16, 2012

    Please, how do I change the transistors to MOSFETs?

    • Oyedele
      April 2, 2013

      Just remove those transistor e.g Q4……..Q9 and replace with mosfet its work well with mosfet…I use mosfet for mine….remember to remove D3 and D4…….for further explanation 08035252105

      • RAKESH
        April 15, 2013

        which mosfet is should be used and how to connect it please send the circuit.

        • Oyedele
          April 18, 2013

          use IRF3205 for high power output…….connect the gate to that 100R resistor directly and eliminates other transistor….

          • Oyinz
            August 14, 2013

            Pls can you give a full explanation of the modified and it connection circuit.

          • August 27, 2013

            Means we have to replace all transistors (from Q4 to Q9 ) by two parallel mosfets irf3205 ??

          • GOHOHO
            June 8, 2015

            AM STILL TRYING IT
            I NEED 500W
            PLS HELP

  • August 31, 2012

    Thank You for posting the circuit on your website,
    PWM inverter circuit :

    But please at least give credit to who made it which happens to be me 🙂

  • SAMU
    August 24, 2012

    I have studied this inverter circuit and compared it to other PWM Based inverters.others are supplied with 12V AT PIN 15 BUT THIS IS 8v . HELP ME WITH AN EXPLANATION.

    • August 31, 2012

      It doesn’t matter, the 3524 has an internal 5 volt regulator. You can give any voltage between 8 and 15.

    August 23, 2012

    suppose I want to use a high frequency transformer like the one used in china’s JEC inverter.What modifications will I have to make to the above inverter?

    • mugeca
      March 25, 2013

      hi kip. just change the frequency from 50hz to like 1khz. i.e change component values between pins 6 and 7.
      try and wish you the best.

  • August 18, 2012

    sir, i am building this circuit for an investigatory project and i would just want to ask a few questions. 1.what is the required dimensions of the heatsink for the driver transistors and the ic 7808? 2. shall i use a 12v 40ah car battery for the supply?.what is the specification for diodes 3 and 4? really need your help,.,.,.

    • August 31, 2012

      7808 doesn’t need a heatsink and the driver transistors too. Use either 4x1n4007 general purpose diodes or a bridge rectifier instead.

      • kiran
        February 13, 2013

        u had workd on diz ckt …cn u giv ur material how u workd and ckt operation …. i am mechinical student…. bt wanna design it.

  • Ajayi Oluwasegun
    July 25, 2012

    I designed this circuit using a 48v 200ah dc input, but when coming ON on load, it keeps tripping OFF. Please advice. Thanks..

    • August 31, 2012

      1-Remove the 2n3055 which could be saturating the power transistors
      2-Make sure R9 is 2.2k and not 22k

  • July 16, 2012

    This is replacement for the transistor to mosfet which i design.I have tried it and it worked excellently.i have used it to build inverter for so many who need inverter.It has high efficiency and it runs cool . still mount the mosfet on heatsink.Try it and give me feedback.If u need the modification of the 250watts to 1000watts with mosfet and also a powerful charger for it contact me on 2348094681539 or email

  • June 26, 2012

    Plz…is gud to replace those TRANSISTOR to MOSFET.. becoz Mosfet switching rate is faster than ordanary bichpholar transistor and hi will preffire Icsg3524 as the best OSCILLATOR ic for inverter project so plz give this circuits involve of MOSFET

    • August 31, 2012

      when you’re talking 50 or 60 Hz there is no need for very high speed as you say. Transistors are OK.

      • Oyinz
        August 14, 2013

        Sorry for this question what is mosfet and how can i mount this circuit on a breadboard

  • hamza
    June 8, 2012

    i want to upto couple instead of the transformer

  • Raheel
    June 4, 2012

    it is a very good circuit for engineers and technicians having wish to be groomed, thank you for presenting it here

  • Sam
    April 18, 2012

    Dear Sir

    I have read the whole article and really appreciate the fact that it supports error correction. However it is a square wave inverter, is it any way that it can be revised to be a modified square wave inverter using same SG3524 or SG3525 IC for mosfets. I have seen many diagrams and yet to see a inverter project for a modified sqaure wave but with stable 220v at its output.



    March 16, 2012

    plz can any one tell what must be the voltage at pin 11 and 14 in this circuit ….
    please help me frnds !!!!!!!!!!!! it will be very helpful for me…..

  • March 13, 2012

    how to choose the rate of current transformer? I have made a inverter 100w, but the transformer is not suitable, so when I use it, the output voltage drop. please help.

  • Ed
    February 11, 2012

    Admin, thank you for the reply Nov10th,2011. I did the right clk and ya know’s WHAT? It WORKED!! Now I can read the parts and now I know something NEW to do with these computors when they work,,,which is why I am late responding,,mine crashed shortly after my question and now have to use the Libraries to go on line. Thanks Ed

  • sudheer
    February 11, 2012

    i am not getting 2n6277 power transistor can any one can tell the equivalent to it.!! i need it urgently

    February 8, 2012

    hi sir ,,,i did your circuit but i am getting very less AC output at the secondary of t2 ,,,that is just 44 volts… what may be the problem sir ???…i used (1/4 watt resistor components except R9 2.2K which is half watt ) & 2n3773 in place of 2n6277 ,now i am not connecting to cro ,so i didnt inserted the fillter circuit ,i used a 12v DC battery..and i connected in bread board!!!!! the last transistor 2n3773 at the lower side getting heated fastly….please help me sir

    • Presoon
      October 29, 2012

      Same problem with me too. I am getting output voltage of 3.6V at pin 11 and 14 and in my CRO, the output shows the square wave form too.. I don’t have the provision to connect both channels simultanoursly. Hence I am not sure if they are switching alternatively.

      When my primary side of transformer is kept open(Between centertap and 12 Side) and check the voltage reading with my multimeter, it shows 12.1 V which is from my powerful 60AH battery. Soon as I connect it to the transformer, the voltage accross the terminal on my primary drops to 6.5 to 7 volts. This is under noload condition. When I checked the current at primary, it consumes around 8Amps. The transistors heats up tremendously.

      Could you please help me Nickk ?

    February 7, 2012

    Thanks a lot Seetharaman sir… i will Trÿ..:)

  • seetharaman
    February 5, 2012

    Hi for pure sine wave generation a function generator chip with driver and output transformers with MOSFETs or transistors to be used, with AGC and other feed backs to be used for stability.

    February 3, 2012

    HI SIR … i didn’t get the answer for ma previous question,but no problem i found the answers…. sir can u give give some idea that how can i get pure sine-wave using this circuit …please sir I’m waiting for your reply

    February 1, 2012

    Hi sir ,,, i didn’t get transistor 2N6227 in market can u please tell me any equivalent transistor… and please tell me what these transistor stages do here…please recomment sir

  • Martin
    January 26, 2012

    how do i obtain pure sine wave please????? urgent

  • Chris
    January 23, 2012

    Hi, am chris.tnks 4 dis cct.pls i want to know if there is any tins to adjust on the driva stage wen makin any one abov 12vdc i.e(24v,36v, 48v etc)apat frm d increas in mosfet and xforma windindin or can d cct go wit just any volt.and pls i also need a batry low shunt down cct 2 incuprate to dis.tanks mail(

  • Francis
    January 18, 2012

    Hi Seetharaman, what about the Charging system of this inverter? is it in the circuit diagram? and i also observe that on the Circuit diagram above, there is no T1 fo transformer. please help out. thank you

  • Henrique
    January 8, 2012

    o coletor de Q1 deve ser aterrado BC327

  • Henrique
    January 8, 2012

    observei um erro no esquema eletrico do circuito o coletor de T1 deve
    ser aterrado DC327

  • Seetharaman
    January 7, 2012

    Hi Eniola it is a Motorola power transistor there is no equivallent. you may use 3nos of 2N3055 in parallel.
    Hi Sim this inverter is more effficient as per load requirement the output is pumped. As there are filter in the output it is a modified squarewave without sharp raise and fall, so connected digital equipment will not get spoiled.

  • Sim
    January 7, 2012

    What are the advantages of this inverter waveform over the normal squarewave ?

  • January 7, 2012

    sir, this is a perfect circuit.. But please I couldn’t get 2N6277 transistor in the market, so which one can I buy in replace of it and that will work efficiently. Thank you sir.

  • Seetharaman
    January 6, 2012

    Hi Sim except where you require only pure sine wave.

  • Sim
    January 6, 2012

    Is this inverter waveform suitable for all kind of loads ?

  • Seetharaman
    January 5, 2012

    Hi Sim it depends on the lamination its permeability etc. That you please leave it to a good transformer designer. You give the spec to them they will take care. specify 10.8-0-10.8volt primary, secondary 230volt transformer with a capacity 300VA.

  • Sim
    January 5, 2012

    What should be the number of turns for the primary and secondary of the transformer windings ?

  • seetharaman
    January 5, 2012

    Hi Naren the two pins are base and emitter. the case itself is collector. Please take advice from electronic hobbyist nearby you.
    Hi Sim you can use for inductive loads but limit the load to 200watts maximum

  • Sim
    January 4, 2012

    Can i use this inverter circuit to power inductive load ?

  • naren
    December 29, 2011

    2N3055 it has only 2 terminals how can i connect it into pcb.

  • Seetharaman
    December 28, 2011

    Hi Prakash all connections shown as ground to be connected to negative of the battery.

  • prakash
    December 27, 2011

    where I have connect -ve terminal of the battery in this circuit.

  • Seetharaman
    December 19, 2011

    Hi Sim can be used. as an additional protection use a 250volt or 270 volt VDR in the out put of inverter.

  • Sim
    December 17, 2011

    Can i use this inverter circuit to power my LCD TV ?

  • Seetharaman
    December 12, 2011

    Hi Sim it is squarewave.

  • December 11, 2011

    Is this circuit a squarewave or modified sinewave inverter ?

  • anso
    November 22, 2011

    hi. there is error on your 7808 regulator pin configuration. the right configuration is pin 2 to GND and pin 3 to IC.

  • anso
    November 22, 2011

    hi. pls can bc337 in your 250w pwm inverter drive 8 pararell mosfet irf3205? pls help thanks.

  • Ed
    November 10, 2011

    Hi everyone, my eyes are not up to par these days, so if I am wrong, ignore this question and remark. Where is the 7805 listed in the related description? And, yeah my eyes,,but is this the worst display of a circuit,,, streeeeeeetched out from top to bottom of page,,I can’t read the parts! what are the numbers on the transistors? Thee only one I am sure of is the “3055” the rest are so blurred from the stretch it’s impossible to read.
    Whats the point of a PWM if it isn’t a modified or simulated sine wave? You could get a square wave with less parts to fail and wind your own M.O.T. to get the amp coverage and use beefy Switching Transistors to handle the demand. This is just an in my opinion over built plain ole inverter.
    If we are going to get that complicated,,at least make it better. A Modified square/ simulated sine wave PWM inverter would be worth thee effort. My opinion

    • admin
      November 10, 2011

      Reply to Ed
      There is no problem with the circuit diagram. It looks compressed because it is a wide diagram and the current theme of the site will just compress it to fit into the content area. Just right click the image and open it in a new tab. Then you can see the diagram clearly.

      PWM is used to keep the output voltage of the inverter steady irrespective of the load variations.

      It is not 7805 and it was a typo error from my part. It is actually 7808 and I corrected it in the description.

      This circuit works well and many have successfully assembled it.

      Anyway thanks for pointing out the error

      • kiran
        February 13, 2013

        sir ….i waana work on dis ckt as my main project…… cn u giv me proper workng of dis ckt ..itz analysis nd …connections ……..i wanna material of it …….how u workd .

      • gim
        February 19, 2013

        Thanks for the detailed explanation of how the circuit works, which I have fully understood. However not all of the circuit was explained.

        Could you (or someone else) explain what the circuitry connected to pins 1,2 & 9 does? This includes Q1, D1, R3,4,5,6,7 and C2,3,5.

        Thank you.

  • Maqbool
    November 1, 2011

    Sir, it is realy a good apparunity to learn about electronic circuits. If it is possible to send me a procedure of testin of transistor and other semi conductors in a circuit or out of circuit by testing meters.
    Thanking you.
    I realy appriciate your afforts to communicate such type of information to tecnical people.
    best regards
    Electrical & Mechanical Engineers

  • October 12, 2011

    Hello everyone can someone help me on this > i built the circuit but when I put load on the voltage still drops what could be my problem. Thank you

  • seetharaman
    October 11, 2011

    Hi Nayeem D3 and D4 can be 1N5404. S1 is for on off for the inverter.

  • Nayeem
    October 7, 2011

    please say me the values of diode D3 & D4
    & in circuit diagram what is S1 is it a switch r not


  • Alex
    September 29, 2011

    Can someone answer me please I need some help here

  • Alex
    September 27, 2011

    Hi is this a modyfied output inverter. Thank u

  • Alex
    September 27, 2011

    Hello I love this circuit I built another circuit and the output decreases with load but according to ur inverter this should not happen. Is this a modified sine wave output. Looking for your reply just now . Thank you keep up the good work

  • charles
    September 25, 2011

    Hi man, nice work here. pls can i get a pure sine wave inverter diagram of this nature. thanks

  • emperor
    September 25, 2011

    Pls bro,have tested this circuit and it worked out perfectly well. but my problem is that: 1. Can i build it on 24v transformer. 2. can i get a better cct for charging my batteries(12v 100amp * 2 with charging cut-off included because two of my batteries have been damaged due to overcharging. 3. can i get a cct to monitor overload of the inverter. pls i dearly need a response,or if u can send me your personal phone number for a direct contact. thanks in anticipated response

  • September 23, 2011

    hi man and colleque well done

  • seetharaman
    September 19, 2011

    Hi Mike the output will be pure square wave.

  • MIKE
    September 18, 2011

    hello sir,

    What kind of output wave?

    Modify sine wave? or pure sine wave?

    plz, recomment~

  • August 9, 2011

    Hello sir,
    I need all the details about inverter can you pls send me about that.
    Thank you sir.

  • ranie ymbong
    August 8, 2011

    thanks for the power inverter design that can be used for a standby power supply for our computers

  • August 8, 2011

    hi sir! can you post a design on how to make a simple solar energy which outputs 12V DC? I really need it.Thank you

  • August 5, 2011

    I find this type of circuit and now got it thanks for post this circuit

  • August 5, 2011

    I just love this,component list and construction of a 1000watt or 850watt power inverter. please i really need it

  • Nitesh
    August 4, 2011

    hi sir can you publish the design,component list and construction of a 1000watt or 850watt power inverter. please i really need it. you can also email it to me at

  • Pankaj Jha
    August 3, 2011

    Hi, I need a Circuit Diagram which produce +15v and -15v from 24v DC power supply

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