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




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 "I made it" 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" size recommendation:
(Power) (Supply) (Transformer 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.

Note15-Feb-16: (48V center tapped means: P:48V "24-0-24" / S:220V)

Note18-Feb-16: Test your transformer before doing this project. Disconnect the transformer from anything it is attached to, connect the 220v Secondary side directly into a 220vAC outlet and test the Primary side with your voltmeter, you should get exactly the voltage necessary for this project as per the table above. If not then don't waste your time building the project, it will not work.

****Do not supply the driver circuit with more than 24VDC max. because the voltage regulator "7812" will burn. Look at the pic of how to connect the batteries and where to take a 24vDC wire from.

3> R1 is to set the PWM duty cycle to 220v. Connect a voltmeter to the AC 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 substitute 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 are heat sensitive, they change value when 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 inverter like "overload cut-off", "low battery cut-off" or "overheating cut-off".

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 thick black lines on the schema also I included a pic so you see how thick those wires must be. (You can make the driving circuit section on a breadboard for testing purposes but NOT the power stage).

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 separate 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 heat-sinks.

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, it just sounds a buzzer.

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, and yes equivalents work too.

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.

Update 18-Feb-16: There are cheap readily available, professional looking Battery level indicators these days for a couple of $, consider them in your project. LED meterLCD meter

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.

22> Testing the circuit on a
breadboardwith crocodile clips or thin wires WILL NOT WORK ! You'll get wrong voltage readings. Don't come back crying that you're getting a 150v output or so.

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1,855 Discussions


5 days ago

Hello Mr Nick, what are the voltages of the electrolytic capacitors in these schematics?


25 days ago

Anyone know how to make this circuit output a sine wave instead of square wave? Because square wave isn't good for sensitive electronic households like: electric fan, TVs, etc. I read somewhere that you could use 4017 IC to output a modified sine wave. Please reply thanks


8 weeks ago

Hi Nick, it's me again. I finally built my first inverter based on your schematic (the one with MOSFET) but I replaced the IRFP250 and use IRFZ44N instead. I also removed the feedback transformer and connect the bridge rectifier (I used KBP307, with 3A ratings and 600V max. voltage) directly from the main transformer.

The problem now is the inverter didn't work. I measured the voltages across the MOSFET without the transformer connected to it. The probes connected at the 'Drain' pin of the MOSFET and the others at the CT input of the transformer (or the Vcc which is 12 V in). The results are both of them had a different voltage, one MOSFET shows 10.1 V and the other one shows 5.78 V.

When I connected the transfomer to the terminal block (which contains two MOSFETs and 12V Vcc) to the the transformer primary windings (12-0-12). I measured the voltage drops at the main input terminal and it shows about 8V-to-11,1V while the battery is measured at 12,67 V.

And also the MOSFETs seem only work alone (The ones getting very hot and sometimes the two getting hot together) these conditions can be swapped, I mean it can be the upper MOSFET connected to the pin-14 or the MOSFET at the pin-11 of the SG3524 that getting hot while the other stays cold.

Here's my schematic diagram compared to yours.

3. 250 to 5000 Watts PWM DC-AC 220V Power Inverter.jpgInv. Sam.png
2 replies
use your brainwh1teshadow

Reply 5 weeks ago

there is reason he is using feedback transformer. if you don't like the additional transformer, you can use separate power supply 12V. the ones you are using with (resistor 220K) giving you about only 3V output (simulated with everycircuit) just look at the output bridge, he is using 10uF that's why peak voltage dropped and down to 3V with 12V 30mW load. that's why you never reach any point to turn this IC on.
you can't "hacking" circuit with only voltage divider resistor. try with author intention first design if it works, then you can try to build "custom" as you like.

WhatsApp Image 2019-08-16 at 4.40.49 PM.jpeg
wh1teshadowuse your brain

Reply 25 days ago

Problem solved. I accidently shorted the power stage and it causes the FET to generates high heat due to the high current drain. Thanks for your answer anyway.


5 weeks ago

Hello Nick,
is PWM inverter same with pure sine wave inverter? and, can the power transistor be replaced with IGBT ? thanks


6 weeks ago

Dear Nick,
Would please be so kind to email me all the schematic diagrams for this project as I'm not able to view it on instructables please sir, my email address is clivaro@gmail.com. We have a lot of power outages here, please help.


Question 2 months ago

where can I buy CT Transformer that is centre tapped on the primary side having the following specs. (750w) (12VDC) (P:24V "12-0-12" / S:220V)?

1 answer

Reply 2 months ago

Hi Rookie12345678,
I don't think you'll find a ready made trans., you'll have to custom make it. Research your area on who custom makes such things.


Question 2 months ago

Hi there

Do you know where I can any CT Transformer that is centre tapped on the primary side having the following features?
(750w) (12VDC) (P:24V "12-0-12" / S:220V)

By the way, I like your work

1 answer

2 months ago

hi sir , i have a question regarding about the transformer, i want to rewind a transormer 12- 0- 12 to 230vac 5000 w or 10000watts, instead of rewinding 84 -0 -84 v to 230 vac 5000w to 10000w . my question is what is the difference between low voltage in the primary at higher wattage output ? is there any effect to my power output transistor? i decide to rewind a 12v in the primary section because if you rewind a higher voltage in the primary section, more batteries are needed and its expensive, please give me an idea. thank you very much sir.

1 reply

Reply 2 months ago

Hi ArnelD6,
From your question it's very obvious that you don't know what you're doing :)
1- A single 12v battery can not give 5000w by itself.
2- There is no enamel copper wire gauge that I know of to wind it as 12v/5000 w.
Stick to the original design and only to the original design and charts !


2 months ago

I made 1000watts inverter circuit with a feedback modulation 12v DC to 220v ac.
Without load 220v I plugged fan of 35watts the voltage of the battery is dropping out faster and mosfet getting hot. I seriously need help. Thanks

1 reply

Reply 2 months ago

Hi PhilipO36,
Please show us your setup, specialy your battery size, wiring between battery and transformer.

Hi. I made this project. It gave me 220v AC without any load and there was no problem. But when I take a little load(about 60 watts) the voltage reduces about to 150v. My projects 1000 watts. Piease help me.

1 reply