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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MarkM171 hour ago

Hi Nick

This looks awesome, and we know it works as you have one. :-) I am going to start this coming week to build it. I am not a Pro Member yet. Will it be possible for you to send me the PDF (and other files) i require please.

I will first do the one you have here then try the 1500 watt unit.

Thank you very much, keep up the great designs.


kevgsw4 days ago
(removed by author or community request)
kevgsw kevgsw4 days ago

Is there a way to make this inverter work with a voltage multiplier and extra batteries at the power stage in place of using a transformer?

jluga5 days ago

can u help me make my battery not to drain,,so that my inverter work round the clock 24 hours a day. thanks to ur reply,my email

jluga6 days ago

hi nick,i built ur power inverter,,and it work good,thisis my diagram it means a looping power,is it imposible my circuit is self charging,my charger can't charge enough to my deep cycle 40ah battery..correct me if i'm wrong,i need ur reply..thanks and more power to u sir :)

Nick_Zouein (author)  jluga5 days ago

Hello jluga,

No things do not work this way. A closed loop circuit will eventualy drain the battery empty, I've answered similar questions earlier.

jluga6 days ago

my load are 1pc 11 watt bulb,1 fan and 1 battery charger,


hi i'm making an 300W inverter based on your circuit, how will I know how many ampere the transformer is?

instruct8393 months ago

thank you sir Nickk for sharing this good inverter. i am trying to make this one for my house using a solar but the voltage value of electrolytic capacitors are missing and the value of bridge diode also is missing. can you please tell me what is the value of said components.. thank you

Nick_Zouein (author)  instruct8393 months ago


hi nick

chould you email me on

Thanks in advance

Love your design sir!. I want to make a inverter that gives like 48 V with 400 W so basically the transistors will have to be added and with V+ changed, any other change do you think should be given here?

Love your design sir!. I want to make a inverter that gives like 48V with 400W so basically the transistors will have to be added and with V+ changed, any other change do you think should be given here?

muffrin made it!16 days ago

mr nick this is my inverter i make it with your circuit ,my custom made transformer i wind it myself by doubling my primary wind as i told you before ,an just to let you know that how ferite transformer wind too for it to work best i used the same method



Hi Nick , I could not find the part 2N6277 , but can substantivadamente equivalent of MJ10015 MJ10016 and ?

muffrin1 month ago

Mr nick let i share something which i done and it work perfectly ,i didn,t have a large wire to wind my transformer 12-0-12 primary side of the tranny the wire size was 16# what i done i parallel the 16# then i wind the pirmary side of my transformer an it work perfectly , i done this before in my experiment with other circuit an it work good ,ok , what do you think about that ?.

Nick_Zouein (author)  muffrin24 days ago

Strange ! I didn't know that this works. nice info.

Good Day, Gentes ...

I would like to know how to find out how many volts is required for each
operation :

"250 to 5000 wallts...."


0.1uf .... volts ?

1uF ....

10uF ....

20uf ...

47uF ...

104 = 0,01uf ....

I descupla , I am Brazilian

Thank U.

Nick_Zouein (author)  bemsatilitys0324 days ago


TarasG29 days ago

Somebody have layout format file? If have, send me please on

ulywae1 month ago

woow very nice,, and I connect this circuit with optocoupler. So I do not use a small transformer

JohnA131 month ago

Hello Nick,

Are you saying that this your circuit drawing above can handle 12 Volts, 24 Volts etc or do you another circuit drawing that can handle 24 Volts and above. pls reply. sure sure
SilvioD JohnA131 month ago

Yes the circuit is powered via a voltage regulator thus the control circuit works with 24 volts and possibly more. The transformer primary has to match the working voltage though.

SilvioD1 month ago

Hi Nickk I have been looking at your circuit and I plan to modify my existing inverter which has a 10-0-10 pri. and 220v sec.with tappings up to 240v with 10 volt intervals. I am using a couple of BUR 52 at my output stage which are very powerful and are giving me around 440-500watts of output power. I cannot operate inductive loads on it as it is a square wave. Is your inverter a modified sine wave, a pure sine wave or a square wave? I am planning to use mosfets in my output stage which are IRF 1405 which are also very powerful and rather cheap to buy. Is your circuit possible to be converted to mosfets instead of transistors?

MohamedA191 month ago

Hello Nick,

One more question, How this low battery circuit will work on more than one 12v battery.

MohamedA191 month ago

Hello Nick,

I need to detect the AC main for turn ON/OFF inverter, could you please suggest that how can I achieve this?

dejanb1 month ago

Hello Nick! This is a great project!

Before i start to build this inverter, for my solar powered home i need information how much current inverter will draw from the battery, with no load at 220v in 1500w 24VDC version?

Best Regards!

josfemi made it!2 months ago

i never had issues with feedback as many people complain and it has greatly work for me, with little modification, nick pls i do i get the programing for the sine wave pls

herryau2 months ago
Hello Nick,
I have made the inverter based on your design with the mosfet version. But i found that the output voltage drop around 10 volt after i connect with 5 watt lamp. I use 2k2 variable resistor as well to set 220vac.and i use 4 irfz44 mosfet and standard transformer 5 amp. Could advise what should i do to avoid the voltage drop?
Nick_Zouein (author)  herryau2 months ago
please upload some pics to see your setup.
Hello Nick, please find the picture about my project.
Vickylbee3 months ago

Hello Nickk, please help! On no-load my inverter works well with 201Vac output which is ok for my use. But once i load it the voltage drops drastically to about 120Vac. I have bought a brand new 75ah battery, wound a custom made 12-0-12/240/12/14Vac transformer that could accommodate even my battery charger when completed, and connected everything as you shown and described. I suspect my feedback section is not working because i adjusted R1 from min to max and measured 1.42 and 2.04Vdc respectively. I used 7812 and i noticed Vdc at pin 11 and 14 remained around 4.5V and didn't change when i varied R1 from min to max.

What could be the problem this time, please?

Nick_Zouein (author)  Vickylbee3 months ago
how many amps is your custom made trans? can u upload a photo to see its size .

See pix...

vicIMAG2093.jpgvicIMAG2094.jpgvicIMAG2095.jpgvicIMAG2096.jpgvicIMAG2103.jpgVickylbee InverterIMAG2097.jpg
Nick_Zouein (author)  Vickylbee3 months ago

1- Is your 12vdc battery fully charged? connect voltmeter and see if it drops below 12vdc while inverter is ON and loaded.

2- Disconnect the 12vac "feedback" that comes from your custom made transformer and connect an external 220/12v small transformer "0.5 amp is enough" to the feedback section.

3- Did you install a 2.2K variable "R2" ? because this part is hard to find, or did u install something else?

4- What is the load that your putting on the inverter?

5- I noticed that your wiring that goes to the power section "trans and transistors" is not thick enough, this also causes a drop in voltage, it happened to me when i was in the testing stages. See on the schematic diagram where you're supposed to have thick wirings, they are marked in Bold. also see my pics and notes on the thick wiring and have an idea how thick the wires should be.

Please check the above steps and send feedback.

Hello Nickk,

Firstly my response to your above questions are:

1- Yes, its a new, fully charged 75Ah, 12V battery and it does not drop below 11.8V when inverter is ON and loaded

2- I installed a small transformer at feedback section and the outcome was the same

3- Yes, its 2.2k variable. All components were of the values in your schematic

4- I tested with 200W incandescent bulb and a 100W soldering iron

5- Thanks- your observation helped. I increased the wire size as you can see in picture

Infact, i reconstructed the circuit but noticed the same problem- my feedback section at maximum duty circle drops output voltage to 147V from 210V when i load the inverter with 300W bulb and soldering iron load. I noticed when i varied R2 with no load my output voltage varied from 210v to 145v. Varying R2 doesn't give higher than 210v. I think the problem may be from the feedback section but i can not find it.

What could be the problem- please help!

The waveforms from top to bottom are that of the output voltage, IC pin 11 output, and the main transformer input

I have added photos. The transformer is 1kva, battery 75ah, power trans 2n3773. Also see waveform from 3 channels of my oscilope- blue (top) T2 output, blue (middle) T2 12v feedback, and grey (bottom) T2 input.

So what could be the problem, please.
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