250 to 5000 watts PWM DC/AC 220V Power Inverter

Picture of 250 to 5000 watts PWM DC/AC 220V Power Inverter
3524 pwm transistor ex.jpg
3524 pwm V2-MOSFET.jpg
3524 pwm mosfet ex.jpg
3524 PCB.bmp
This is a heavy duty design of a Pulse Width Modulator DC/AC inverter using the chip SG3524 .
I've been using it as a backup to power up all my house when outages occur since aprox. 6 years non stop.

If you like the work and intend to build the circuit don't forget to click on the "follow" button so I know how many people benefit from the design, Thanks.


1> The schematic circuit design is for a 250 watt output, while the pics are of my 1500 watts inverter that i built, to increase the power of the circuit you have to add more of the Q7 and Q8 transistors in parallel, each pair you add will increase your power by 250 watts, ex: to get 750 watts of power from the inverter you need to add in parallel 2 of Q7 and 2 of Q8 to the original design.

2> If you increase the power transistors you have to enlarge the T2 transformer to match the new needs, the circuit's transformer is rated 25 amps to handle 250 watts of 220v, for every 1 additional amp you need on the 220v side you have to increase 10 amps on the 12v side, of course there are limits to the thickness of the winding so if you need more than 750 watts i recommend that you use a 24VDC supply instead of 12 volts:

DC voltage and Transformer "T2" winding recommendation:
Power     Supply     Winding
750w       12VDC     P:24V "12-0-12" / S:220V
1500w     24VDC     P:48V "24-0-24" / S:220V
2250w     36VDC     P:72V "36-0-36" / S:220V
3000w     48VDC     P:96V "48-0-48" / S:220V
3750w     60VDC     P:120V "60-0-60" / S:220V
4500w     72VDC     P:144V "72-0-72" / S:220V
5250w     84VDC     P:168V "84-0-84" / S:220V
*The transformer should be "center tapped" at the primary side.
**You can make the secondary 110v if needed.
***The transformer in the pic is a custom made (48V center tapped / 220v ) 2000 watts, weights like 10 kilos.

3> R1 is to set the PWM duty cycle to 220v. Connect voltmeter to the output of your inverter and vary VR1 till the voltage reads 220V.

4> R2 is to set the frequency to 50 or 60 Hz (R2 range is between 40Hz to 75Hz), so guys that do not have a frequency meter are advised to blindly put this variable resistor mid-way which should drop you in the range of 50~60 Hz.
If you want you can substitue the variable resistor with a fixed resistor using the following formula: F = 1.3 / (RxC)
in our case to get a 50Hz output we remove both the 100K and the variable 100K both from pin 6 and we put instead a 260K fixed resistor and we leave the 0.1uF (the 104 cap) as it is, this change should give out a fixed 50Hz as per the formula :
1.3 / (260,000 ohm x 0.0000001 farad) = 50Hz
But in reality it will not exactly give 50Hz because the 260K resistor has a specific error value margin so does the capacitor, that's why i recommend a variable resistor so that accurate calibration can be achieved.

5> Use either tantalum or polyester film "as in pic" for the 104 caps, ceramic disc caps change value once hot and this in turn changes the frequency of the inverter so they are not recommended.

6> Pin 10 of the SG3524 can be used to auto shut down the inverter, once a positive voltage is given instead of negative to pin10, the SG3524 will stop oscillating. This is useful for persons wanting to add some cosmetic makeup to their inverters like overload cutoff, low battery cutoff or overheating cutoff.

7> Wiring connections on the power stage side should be thick enough to handle the huge amps drain from the batteries. I marked them with dark black on the schema also I included a pic so you see how thick those wires must be.

8> The design does not include a battery charger since each person will be building a custom version of the inverter with specific power needs. If you are ordering a custom made transformer you can ask them to take out for you an additional output wire on the primary side to give 14v (between point 0 and this new wire) and use it to charge a 12v battery, of course this needs a seperate circuit to control charging auto cut-off. But anyway this is not advisable because it will shorten the life of the transformer itself since using it as a charger will toast the enamel coating layer of the copper wires over time. Anyway .. YES can be done to reduce cost.

9> A cooling fan will be needed to reduce heat off the heat sinks and transformer, i recommend getting a 220v fan and connecting it to the output T2 transformer, when you power up the circuit the fan will start this will always give you a simple way to know that 220v is present and everything is OK.. You can use a computer's old power supply fan if you like.
Note that the fan must suck air out from the inverter case and NOT blow inside, so install it the correct way or it will be useless.
Also note how I fixed both the heat sinks and where the fan is, in a way that the fan sucks hot air from like a channel between the 2 heatsinks. 

10> 2 circuit breakers are recommended instead of fuses, one on the DC side and one on the AC side, depending on your design
Ex: for a 24vDC ( 1500 watts design ) put a 60Amp breaker on the DC side and a 6Amp on the AC side.
For every 1amp of 220vAC you will be draining like 8 to 10 Amps from the 12v battery, make your calculations !

11> The 2 Heat sinks should be big enough to cool the transistors, they are separate and should NOT touch each other. "see the pics"

12> Important: If you're building a big design that uses more than 24VDC as power source, make sure not to supply the driver circuit with more than 24v maximum. (EX: If you have 4 batteries 4x12 = 48v , connect the v+ supply of the driver circuit to the second battery's (+) terminal with a thin 1 mm wire which is more than enough. this supplies the driver circuit with +24v while supplies the power transformer with +48v) "see the batteries pic example"

13> "Optional" : Deep Cycle batteries are your best choice, consider them for best results .. read more

14> Be cautious when building this circuit it involves high voltage which is lethal, any part you touch when the circuit is ON could give you a nasty painful jolt, specially the heat-sinks, never touch them when the circuit is on to see if the transistors are hot !! I ate it several times :)

15> The optional "Low voltage warning" is already embedded in the PCB layout, you can disregard it and not install it's components if you do not need it. It does not affect the functionality of the main circuit.

16> The Motorola 2N6277 is a durable heavy duty power transistor, it is used in many US tanks for it's reliability but unfortunately it is a very hard to find part, instead you can substitute each 2N6277 with 2 x 2N3773 or any equivalent.

17> I've included an optional "Battery level indicator" circuit diagram that has 4 LEDs, you can see it installed on the front panel of my inverter pic, it is functioning great and shows precisely how much juice the batteries still have. I have included a small relay that is powered by the last LED to auto shutoff the inverter once last LED is off.

18> Also included an optional "Overload circuit", it is very easy to build and can be calibrated to the desired overload current threshold cutoff point through the potentiometer VR1.
R1 is rated 5watts for inverters upto 1000 watts. For bigger versions of the inverter like 1000 to 3000 watts inverters, replace R1 (1 ohm, 5watts) with (1 ohm, 17watts) which should handle loads upto 10 VA.
Make sure you install a proper relay to handle big current drains.

19> Please guys take your time to read and understand my notes, browse and read the posts and questions asked by others because there are many useful information listed in replies. The main reason for me not answering your question is because it has already been asked before and answered upon.

20> It would be nice and inspiring for others if you take some photos and show us how you built your version, any additions to the circuit are mostly welcomed to be listed here, we can all benefit from them.

21> Please click on the "I've made it" button/icon if you did build the circuit so I know how many people benefit from this design.
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Vickylbee6 days ago

Hello Nickk, it works! I found out the problem was that one of the T2 input diodes, D1, had failed close (shunt) and thereby shunting one section on T2 input which resulted in giving half of the expected output voltage. Then i removed D1 and D2 and it works well. At last!

I will now add other protective function, voltage display, buzzer, fan and more cosmetics to it.

Thanks Nickk for sharing your knowledge. I have actually attempted to construct different PWM inverter circuit over the years and this is the one that has worked! Thank you, thank you, and thank you...

i cant find any diode D1 D2 you mention on this circuit

They are at the transformer T2 input side

nickk (author)  Vickylbee6 days ago

Great.. :)

eeteddy6 hours ago


eeteddy6 hours ago

hello nick,

chivindwe21 days ago

Sir, this circuit keeps blowing off my 2n6277 transistors at start up. The two banks of transistors are isolated and I am using a 36V bank of butteries.Could it be that my transformer is too big? I have also since put the cooling fans on top to extract heat instead of blowing from below. I have been testing with a pair of transistors at a time (to get 250W) on this transformer hopping to get satisfactory results before I switch on all the 48 transistors but to no avail. Each time I try to switch on, the 36V burns my test pair of transistors on this huge transformer and that has not made me confident to load the whole set of 48 transistors. It is particularly the base-emitter junctions that gets cooked. I also have the feedback transformer connected ok. Please help.

nickk (author)  chivindwe19 days ago

No the transformer size does not matter. It seems your pinout connections on the 2N6277 are wrong, look into that. Also check if your transformer is functional by disconnecting it and applying to it 220vac and testing to see if you get 36-0-36 on the other side.

chivindwe nickk18 days ago

Thank you Mr. Nickk. I think that my beloved transformer was the problem. Yes applying to it 220vac was giving me 36-0-36 on the other side. However, applying to it 36-0-36 was immediately sucking in 10A even when the other end was still open. This means my test pairs of transistors were being subjected to 360W of power. I have sing ordered a new 48-0-48 to 220 transformer from somebody who winds transformers. I think things will be fine now. I will report back in two weeks time. Have a blessed day today!!

Hell Mr. Chivindwe. I think 1 pair of 2N6277 transistors(250watts) cannot handle the transient current of the transformer you are using since your transformer is too big.

1 pair is not enough to handle the transient current.


mo7md-91 made it!3 days ago

hello nick, in your comments you said LM3524 and SG3524 is the same, but in design using LM3524, you need to connect pin 2 with pin 16 directly and pin 9(comp) with cap 10uf . so my question why you used the following components that i assigned in the attachment picture i wait your answer ?

lalailama4 days ago

Hello Nickk,

Thank you for your sharings, I'm going to try to implement it and maybe some customizations. Only one question so far, what are you using the BC327 connected to the COMP(9) pin for? It seems that by default it's connecting this output to ground, due to fact that base connector is connected to Ref Out (5v), that means to me it is not going to work properly. Let me know if I'm wrong.

Thank you

Vickylbee23 days ago

Hello Nickk,

Firstly i want to thank you for your assistance and generosity.

I have reconstructed my circuit on a PCB but i still got the following problems:

1) the output voltage is about 110Vac, then after some time it drops to 100Vac, 97Vac and then 87Vac...

2) the input voltage for T2 from the center to each end terminal is about 7.5Vac. My battery voltage is 12.4Vdc though

3) the voltage at pin 11 and 14 are 3.5Vdc

I have attached photos. So what could be the problem here, please.

nickk (author)  Vickylbee22 days ago

Is your regulator 7808 ?

Vickylbee nickk22 days ago

Yes, its 7808. See photos- I haveadded it again...

nickk (author)  Vickylbee19 days ago

please replace by 7812 and send feedback.

Hello Nickk, it works! I found out the problem was that one of the T2 input diodes, D1, had failed close (shunt) and thereby shunting one section on T2 input which resulted in giving half of the expected output voltage. Then i removed D1 and D2 and it works well. At last!

I will now add other protective function, voltage display, buzzer, fan and more cosmetics to it.

Thanks Nickk for sharing your knowledge. I have actually attempted to construct different PWM inverter circuit over the years and this is the one that has worked! Thank you, thank you, and thank you...

Vickylbee nickk22 days ago

I am suprise that it has not been a problem or noticed by others, but by the formula you gave, F = 1.3 / (RxC), then the 100k resistor and 100k pot R2 will not give f=50Hz, except 200k resistor is used. Can you please also expain that to me. I also notice varying R1 did not change my output voltage

Pls I need to pcb file (Or Img file) for this circuit !


Good day sir, i have a few questions..

1.Is this circuit of yours can run electronic gadgets such as laptops,etc?

2.Is it the output waveform is square wave when we don't connect the filter caps 2.2uF and 0.1uF's?

AliiA22 days ago

Dear Sir Would you please let me know what the characteristic of transformer , I maen the Number of turns In primary and secondary and thickness of diameter in mm for each side .

With my best regards

Good morning sir ;

i have the same question of Vickylbee

but the o/p voltage of me inverter is around 196 volt but if i loaded it ,the voltage drop occur and became 170

so the feedback doesn't work or what sir

what should i do ?

thank you

nickk (author)  mohamed.ibrahimgaber22 days ago

Please upload some pics showing your setup

hello sir

i'm sorry i can't upload pics but i did as this one attached

can u explain how ic sg3524 recover the drop in voltage and how the

feedback work

thank u

jjaan23 days ago

Hi sir kindly tell me that i am working on solar based motor system so i am getting very high costs from market i have to build my own and i like urs so is it efficient for 200w panels to used for water pump1/2 horse power ?secondly sir if yew have charge controller circuit diagram then needed urgently for implemantation?thanks

NelsonC123 days ago

hi nick, i'm planning to used IRFP260N to produce a 1500 watts 24 volt how many mosfet can i put in the circuit. thanks!

Vickylbee1 month ago
(removed by author or community request)

I think there's something wrong in your wirings or connection.. I got that low voltage too when i accidentaly connect the TIP122 in wrong connections. Or maybe you have a wrong pcb design.. just an opinion sir.

I disconnected the entire circuit and rebuilt it but I still got 54V. I use bread board so its easy to reconnect or modify, then i would transfer to PCB if it worked on the breadboard. Ok... I will reconnect directly to a PCB to see if it works fine. Thanks, Aldrin for your insight!

You are welcome sir. I just want to know you that i built this circuit and it's working great! Thanks to Nick for his GREAT FREE SCHEMATIC!! Godbless

nickk (author)  Vickylbee1 month ago
please upload photos of your work.
Vickylbee nickk1 month ago

I have uploaded the photo. I constructed mine on a breadboard for ease of modifications, and would transfer to PCB if it worked. Though my construction looks untidy but I actually test all connection to ensure they are correct. I have rebuilt it at least 6 times and its frustrating that i get 40-55Vac each time. I will reconnect on a PCB to check if that solves the problem.

nickk (author)  Vickylbee1 month ago

Hi, I can't open this file. I need to see what you're doing, trans size, batt. size..etc.

I can blindly assure you that 1000's of people built this inverter and they are all happy. There is some mistake somewhere, I suggest you build it directly on a pcb board.

tmsantos26 days ago

can send a video image with working

baldrin1232 months ago
(removed by author or community request)

try to remove the diode in the transformer.... i have made this circuit and it is working very well without the diode.

im using a 12-0-12 1500 Watts transformer

Thanks to nickk for sharing this... God Bless!

doide is important to safe transistor or any component from short or back voltage

nickk (author)  baldrin1232 months ago


You need a battery power source to power up this circuit, you can't run it on some small transformer as a DC source.

shida5 months ago

hi nikk plz can you help mi

am dont speek englash but

سوالي الوحيد لك ما عو نوع ترانزيزستور او الموصفت المستخدم في صناعة انفيرتر يتكون من 10 بطارات يعني 120 فولط مستمر ولك كل الشكر

Eng_MYM shida2 months ago

عزيزي .... الناس دي مش بتتكلم عربي ...
لكن أحب أقولك إن الموسفت اللي في الدائرة يستحمل لحد 200 IRFP250فولت ... يعني هي هي الدائرة لكن تغير بس الترانسفورمر 2 ...
بدل 12- 0 -12
و طبعا الخارج بتاعة زي ما إنت عاوز
ربنا يستر و يطلع كلامي صح ....ههههههههههههه

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