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 needed. 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.
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eeteddy5 days ago
gmilic9 days ago

I will send you my pictures of your realized project,it works one year!off greed system

Hi Nick, first of all excellent work! I have some old trashed UPS's parts that I'm planning on using for this project and I will need your expertise.

1. Can this transformers be used ? they came from Smart UPS 5000 (APC). They are connected in series to reach the 24v.

2. I was also planning on using the Power Transistors from the same UPS they are 75639P Mosfet 56A 100V N-channel ultrafet

3. Can someone provide eagle files with the PCB or PDF to print and etch ?

Thanks to you all.

photo 1.JPGphoto 2.JPGTransformer.pngphoto 1.JPGphoto 2.JPG
eeteddy25 days ago
eeteddy26 days ago
eeteddy26 days ago
eeteddy26 days ago
dessi1 month ago

hi nickk i made it twice and it works very well

dessi made it!1 month ago

thanks nick


Hi nickk, can I use IRF3205 mosfet instead of IRFP250 mosfet ? How much watts give each pair of IRFP250 ? For 750 watts how many IRFP250 mosfet require?

hamub1 month ago
Nikk may you kindly post thee charger schematics since you said have
chiunit21 month ago
Please nickk Iv spent more than 7$ looking for MCT2E and dint get it. Most people sell 4N35. Please can I use 4n35 insted of mct2e. If yes is there any other modifications I can do?
LordB11 month ago
Hi! The black component beside the 2 Potentiomers is called what??

It's a buzzer so you know that your running out of batterie.

destroyfx1 month ago

Hi nickk,

I want to build this inverter to replace my current defective inverter on my solar system. I was able to get all part except the SG3524. But, in my current inverter, I have not one but two KA3525A and it look like they are SG3525 equivalent! But the pineout is not the same than the 3524 so I adapted the circuit for the chip based and your schema and some other reading. If you have time, can you tell me if the modification is fine?

chiunit21 month ago
Please I need a simple circuit that will
delay my relay change over circuit to
charge, to prevent current inrush because
I used the same transformer for charging
and it burns my fet went charge current
come in. Please I really need it
nickk (author)  chiunit21 month ago
A "time-delay relay" is your best solution, these are available at electrical stores they are cheap, reliable and easy to setup.
cgodson2 months ago
Please I need a simple circuit that will
delay my relay change over circuit to
charge, to prevent current inrush because
I used the same transformer for charging
and it burns my fet went charge current
come in. Please I really need it
cgodson2 months ago
Please I need a simple circuit that will delay my relay change over circuit to charge, to prevent current inrush because I used the same transformer for charging and it burns my fet went charge current come in. Please I really need it
ssrivastava112 months ago

My 1.5 kVA inverter setup directly converting DC coming out from Solar Panels to AC and it is happily running the water pump.

nickk (author)  ssrivastava112 months ago

Thanks for the pics. Glad to hear your positive feedback.

dshokoya2 months ago

Hello Mr Nickk

I would really like to build this. How how do I start or where do I start from? The information provided here is great. It is the best I have come across yet. Is it possible for you to match up the individual circuits with the picture of the finished product with the list of components in each circuit. Things are not easy to come by where I am. Thanks

nickk (author)  dshokoya2 months ago
Everything you need is already listed for free and in details, take your time to read and review. Start by making the driver circuit diagram, it is the cheapest and most dificult part.
ptiuliutinas3 months ago

Hello, Nickk.
Can i use IRFZ44 in place of IRFP250? If so, what changes in schematic are needed? My transformer will be 12 to 220V.
Thank You.

nickk (author)  ptiuliutinas2 months ago

no changes, sorry for the late reply

I have a problem with IRFP250: i'm using my inverter in car and everything was ok with 2N3055, but with IRFP250 inverter only works, when engine is not running. When i start the engine, IRFP250 immediately overheats. Load on inverter is always the same.

Why would this happen? Sorry for my bad English and thank You for Your help.

nickk (author)  ptiuliutinas2 months ago

when the car engine starts the car's dynamo starts charging the 12v battery thus raising the voltage to 13.8vdc, actualy this should not be a problem unless your dynamo is malfunctioning and raising the voltage above 13.8

Please test what the DC reading difference is while the engine is OFF and ON

Already checked this, dynamo charging 13,5V so that's not the problem. Switched back to my setup with 2N3055 and inverter is working perfectly. Could this be related to IRFP250 working directly from dynamo or some voltage spikes from ignition coil? I don't have oscilloscope to test that for sure.

in can be because of ignition spikes..

see during the rotation of dynamo power is being produced and the battery require higher amps of current to charge so while the dynamo is rotating it can cause voltage or current spikes if you connect a loaded inverter. Spikes happen because it has to deliver the power somehow. this may be the reason.

over heating means the inverter is being overloaded according to my opinion. There might be some short circuiting taking place.

as an electrical engineer i can say that you can use irfz44 as long as you know your current and voltage specifications of your dc input matching with your mosfet

benzal2 months ago

thanks for your nice comment...i will change the transformer to 48 0 48 volts later, i just bought that transformer for testing purposes as a simulator...that's why i'm asking if 13/4" x 4" core is enough or 21/4" x 3" core that can handle up to 3k watts or 5k watts....since i am planning to make a multiple secondary wiring winding using 4 relays to stabilize the secondary voltage to 220vac whenever the battery voltage drops from 13.8 to 12.8 down to 11.8 and 11 volts respectively & auto shut off below 11 AWG #4 magnetic copper wire is enough to handle around 200A?

thank you & best regards,

benzal2 months ago

here's the pics...the first is the output voltage with bulb & grinder running @199.9vac, 2nd is battery voltage @ 12.22vdc bulb on, 3rd is battery voltage @11.99 bulb & grinder running, 4th is a 20A commercial x'former, 5th is the frequency @59.9HZ, 6th & 7th are the voltage @ 235.2 & 234.6vac with only bulb@100watts, 8th is the output voltage @ 200.4vac with both bulb & grinder running...i'm using the salvage chassis of my 5000watts inverter...i was not able to find the specific part # of x'sistors in this inverter due to the part # erasure made from the factory of this i tried to assemble your schematic diagram...i am adding 24pcs of IRFB4710 after i will change the x'former rated @5k watts later...

is it right to drop the voltage to 200.4vac from 235.2vac with a difference of .23vdc in the battery?

is 1 3/4" core window X 4" x'former can handle up to 5kwatts?

i have .1uf/600vac filter, & i'm using 7812 for the regulator...

have a bless day ahead...


i am using my 5k watts inverter in running a 1k watts induction motor in my pneumatic tire changer whenever there's a power failure from the i've decided to make this inverter of yours and planning to supply it with 48vdc...that's why im asking a true sinewave output schematic diagram if it is possible to integrate in this inverter of yours...i also saw your booster type schematic diagram using a 300watts sinewave inverter output as the input to transform to 5k watts

nickk (author)  benzal2 months ago

You did not take my note #2 into consideration, a 20amps transformer can not handle such a load ! Read #2 carefully, it is the most important note to get your inverter properly set with the right parts.

benzal2 months ago

Hi Nickk,

Thanks for the schematic diagram...i was able to make the said inverter using 20 amps x'former 12 0 12 / 220 vac...i used 8 pcs IRFB4710 as the power... VDss@ 100V, RDs 0.014, ID @ 75A...i set the frequency @60hz by loading a 100watts incandescent bulb & it works great with an output of 230vac...i tried loading the grinder @710 watts and it runs, but dropping the voltage to 205vac...

1, Load 100watts bulb = 0.6amperes

2, Load 100watts bulb + grinder = 10amps starting torque then down to 1.6 amps

3, Voltage @ pin 11 & 14 @ 3.6volts

is it possible to raise the voltage @ pin 11 & 14 to 4.5volts?

is it also possible to change the MOSFET to IGBT if yes , can you provide a schematic diagram for it?

Again, thanks a lot loading 810watts running for about 3 minutes the mosfet was not even feel hot still there any possible means to make this schematic diagram to make a true sine wave from PWM by incorporating RC or LC circuit between the oscillator & power output?

Lastly, extend my best regards to your family...more power have a nice & bless day ahead of you...

nickk (author)  benzal2 months ago

Please upload a photo showing your setup and battery size and transformer size.

Is the 12vDC dropping or is it stable exact 12v all time?

Did you install the filters? they shape out the frequency to near sinewave.

Replace the 7808 with 7812

send feedback.

4kd4ker2 months ago
Nice one. Still building mine but pls I will love to ask if the 220 part of the ouput transformer can be made to be 208-0-12 to give us a total of 220 and the 12v end connected to the rectifier bridge so as to save us d losses caused by the second transformer when on idle mode (when there is no load)
nickk (author)  4kd4ker2 months ago
it can be made 220-0-12 and use the 0-12 instead of T1 but I do not recommend this, any spark on T2 will fry your driving circuit.
shida2 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

twyeth3 months ago

hi nickk

can i transformer that is not centre tapped be used, if so how would you wire it in

nickk (author)  twyeth2 months ago

no, only center tapped works here

junior_012 months ago
Hello Nick! I will use 5 pairs of IRFZ46. I need to change the value of the gate resistor and emitter?
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