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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shida4 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 shida1 month 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

nickk (author)  Eng_MYMyesterday


Location:Beirut - Lebanon

فعلا كلامك صح eng_mym

mr:nickk i have a problem i use battery 12v 7ah but it empty fast about 1min why


nickk (author)  makram.morris.9yesterday

Because it is 7ah ! You need at least 70amps.

and the best battery charger circuit you have thank`s

pitong14 days ago

sir can i ask for complete list of materials,tanx

nickk (author)  pitongyesterday


Hi sir Nick! Hope you a have a good day. I just wanna ask if it's okay to use UC3524 instead of SG3524? I think they're both equivalent. That's the one i bought here. Thank you for your GREAT SCHEMA.. I'm so thankful that there's a very nice person like you sharing your knowledge.

nickk (author)  Aldrin Dalaganyesterday

Hi Aldrin, Yes they are the same, I've answered a similar question earlier.

Ctstrphy8 days ago

excuse me sir,, it is about your inverter that is pure sine wave in using a 16f628a,, cause we have a little probem,, in oscillator.... cause there is no output in PWM in the PIC but if we touch the oscillator the pin 6 and 7 will have a output.. what seems to be the problem with this..? hope you will see reply it sir. thank you.

nickk (author)  Ctstrphyyesterday

You're posting in the wrong place.

Ctstrphy8 days ago

sir nick help me.. their is something wrong in our inverter using 16f628a,, because their is no output in PWM unless I touch the 20MHz crystal Oscillator. if i touch the Oscillator their is a output but if i will not touch it their is no output... help me sir...

nickk (author)  Ctstrphyyesterday

You're posting in the wrong place.

adsamtzy6 days ago

Thank you sir, i build this circuit but the oscillator sg3524 get hot, sir what could the fault in the circuit? and i have the overload circuit sir how can calibrate the circuit, secondly if i want to build a 3kv inverter sir how could i select R1 that is current sensor resistor. Thanks.

nickk (author)  adsamtzyyesterday

the 3524 should not be hot at all, there is something wrong with your wirings. Make the basic circuit work first before calibrating anything else.

tmsantos7 days ago

podría enviar por el correo electrónico que quiero hacer uno para conmigo gracias

nickk (author)  tmsantosyesterday

Sorry, but I don't speak your language.

pitong14 days ago

sir nick can i ask,im planning to do this project, what if the power transistor 2N6277

is not available here in my country ill replced it with 2 x 2N3773, these 2 x 2N3773 must be in parrallel connection?

nickk (author)  pitongyesterday

Any equivalent should work.

Yes, you can replace/substitute it instead of 2N6277. Parallel connection.

Vickylbee6 days ago
(removed by author or community request)
nickk (author)  Vickylbee4 days ago
please upload photos of your work.

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)  Vickylbeeyesterday

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.

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!
Vickylbee2 days ago
chivindwe5 days ago

I think that there is an error on NOTE point 18.

"...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." The 10 VA should be 10KVA instead.

It's okay. We're just a man, we can make wrong sometimes. But he means 10KVA.. wrong type only.. Thanks to Nick for the great Shematics!

dessi7 days ago

hi sir

please i want to use transistors IGBT for the power stage

so what version of the inverter must i do ?

transistor version or mosfet version ?

thanks !!!!

Adhim20 days ago

Sir , can i use this circuit for 24V , 1000watt inverter.

muffrin22 days ago

hello mr nick i like your pwm inverter circuit an i already buy all the part an ready to build it but just one question can the 24v primary coil wind over the secondary coil or is it matter which coil wind first 24v on top the 220v coil or 220v on top please help me here

nickk (author)  muffrin21 days ago
usually the thick "24v" wire is always on top (outside). it doesn't matter which is on top but becuase of the thickness and not easy to handle make it as outer.

Hi Nick, I'm wondering what are your thoughts about this pure sine wave diagram?

Also, how could I connect just the driver from the above diagram to the power stage? Sorry not really good at electronics, just trying to learn by myself. Thank youuu

mohe123 days ago

hi can you submit me the complete circuits for the battery charging and i need to ask about the brigde and the transformer T1 in the driver schematic circuit , thanks

mohe123 days ago

hi can you submit me the complete circuits for the battery charging and i need to ask about the brigde and the transformer T1 in the driver schematic circuit , thanks

excuse me sir,, is it possible to supply desktop computer and airconditioning units if the frequency of our inverter is square wave and not pure sine wave? cause our prof is deciding that our inverter must supply a computer or aircondition unit.. thank you again sir.. i hope you will answer it..

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