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.

22> Testing your completed circuit with crocodile clips or thin wires WILL NOT WORK ! You'll get wrong voltage readings.
<p>Hi, i have constructed inverter circuit using SG3524, but its frequency is very high, how can i reduce its frequency and use AC output?? Can u pls reply me fast</p>
Nice work Mr Zouein. Am makin efforts to build the same thing but pls how do i get access to the notes?
<p>Hi Nick, i managed to build this inverter and in the beginning it worked very well until when suddenly it started burning the mosfets. I replaced the 3524 IC together with new mosfets but again they blew off. I am using a transformer which i got from a UPS and i did not custom rewound i just used it the way it is, i later replaced the electrolytic capacitors all of them but no change, in fact the mosfets over heats within 30 seconds even without any load connected please help what do you think could be the problem? am Darlington from Eldoret Kenya East africa</p>
<p>did you solve your problem with the mosfets?</p>
<p>Hi Darlington, the mosfets should not heat without a load unless there is a problem at the transformer side. Check your protection diodes, maybe one of them is cooked. Anyway using 'any' transformer is a diversion from the original design.. many things could go wrong.</p>
Hello .what is the furmula to built the transformer base on this project.ex.the size of the wire and core can u give this?
I have constucted the circuits and am so happy it worked its the 5kv but the problem am having is having a functiona battery charger with autocut off 4 a 12v 400A battery ...pls help its my final year project in school.
Hi Nick i want to ask if i could use diff power transistors in this project coz electronic components availability and the cash to get it is a heck of a problem in my region.
<p>any equivalents should work</p>
<p>Is it a <strong>pure</strong> <strong>sine wave pwm</strong> inverter? Kindly reaspond. Thank you.</p>
<p>Thanks Nick, I made it. but i have problems with connecting the power diodes, when i connect them the way the look in the diagram, it does not work unless i remove them. so i connected them across the emitter and collector of the power transistors. will it protect the transistors that way? thank you</p>
<p>Hello eeteddy,</p><p>Happy to hear that you built one. The diodes are not necessarily needed, you can completely remove them they will not make any effect on the functionality on the inverter.</p>
<p>Thank you, but how do i protect the transistors from shortcircuit?</p>
<p>connect them across the emitter and collector of the power transistors.</p>
please i need a circuit that will convert my square wave inverter to sine wave inverter please<br>
<p>You landed on the wrong page.</p>
<p>You can't use 48v on a 12v design, the transformers are different, see note #2</p>
<p>Its nice to see other's work with undesired punks NAME which done nothing to contribute only act as a leech. :@</p>
<p>Thanks for sharing the circuit. The PWM chip is used to generate a 50Hz square wave signal. I'd rather expected a sine wave signal modulated using the PWM.</p><p>Thanks anyway</p>
hi sir am new here and i need some helps.1st i cnt download your pdf.2nd i cnt figure the voltage of d zener diode on the circuit nd that of the normal diode do i use 1n4007? of d low battery cut off due to d blurines.3rd i need the diagram of the over load cut off thanks.
I need to convert only DC to AC. The DC power source are solar panels. These panels combined together give 1000watts or 1kilowatt. Please help as soon as possible.
<p>Hi Nickk,</p><p>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 &amp; it works great with an output of 230vac...i tried loading the grinder @710 watts and it runs, but dropping the voltage to 205vac...</p><p>1, Load 100watts bulb = 0.6amperes</p><p>2, Load 100watts bulb + grinder = 10amps starting torque then down to 1.6 amps</p><p>3, Voltage @ pin 11 &amp; 14 @ 3.6volts</p><p>is it possible to raise the voltage @ pin 11 &amp; 14 to 4.5volts?</p><p>is it also possible to change the MOSFET to IGBT if yes , can you provide a schematic diagram for it?</p><p>Again, thanks a lot loading 810watts running for about 3 minutes the mosfet was not even feel hot still cool...is 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 &amp; power output?</p><p>Lastly, extend my best regards to your family...more power have a nice &amp; bless day ahead of you...</p>
<p>Please upload a photo showing your setup and battery size and transformer size.</p><p>Is the 12vDC dropping or is it stable exact 12v all time?</p><p>Did you install the filters? they shape out the frequency to near sinewave.</p><p>Replace the 7808 with 7812</p><p>send feedback.</p>
<p>hi nick its been a long time since i post here...i want to know the value of zener diode in the buzzer if i want to supply with 24vdc, and also in your battery level indicator...i am now in the proccess of finalizing this new inverter i made...i tested already the osc with 4.5v at both pin 11 and 14...</p>
<p>im using 7810 for this circuit i will change this later to 7812 since i will use 24vdc supply...i tried already this one in 12vdc....sg3524 and lm324 for the battery level indicator...do i have to double only the value of the parts for the battery indicator so that it will work on 24vdc? about the buzzer is it right to change only the zener diode in order to buzz at around 20vdc?</p>
<p>thanks nick.. <br>I want to try to make it..</p>
<p>Hi nick, I have made it but I have some problem, when i connect the oscillator to the power mosfet, the transformer works but it gives very high noise, I tried to connect the different oscillator circuit to the same power mosfet and it works fine without any noise at all. Could you have any ideal on how could I remove this noise.</p>
<p>Hi Nick</p><p>Thanks for the instructable. Nice detail and solid design. Can you tell me if you made the transformer yourself? If so, do you have the have specs on it, such as primary and secondary number of turns,and wire diameter for primary and secondary?</p><p>Thank you,<br>Chris</p>
<p>Hi Nick, recently purchased a pair off EGS002/EG8010+IR2110 SPWM driver boards with LCD displays from ebay(china), but the data sheet is in chinese. The input is 380vDC, 12vAC, using a H-Bridge to generate the AC power output. How do I best get from 12/24 or 48 volts to 380/400 volts DC without power loss? Or from the circuit you think I can input 12 to 48 vDC, then put it thru a transformer? I have about 10 transformer 6&quot; square transformer cores I can wire up. Many thanks..Adrian</p>
Hi Nick i want to ask if i could use diff power transistors in this project coz electronic components availability and the cash to get it is a heck of a problem in my region.
<p>hello i de like to know if my transformer 12/220v 150VA could work for 3000 watts output! thanks for helping me</p>
<p>150VA is 150 watts with a power factor of 1, so no.</p>
Pls am working on it can i use sound power transister for the power stage ?
<p>hello sir. i want to know if a 12v750w inverter can start a fridge that have a 100w power motor, and if the inverter is pure or modified sine wave.good day</p>
<p>good day sir,I want make your inverter.but i have some miss understand,about power transistor, and mosfet.that both has to use in same circuit or one of that only need .if both need to use,how to connect that pin number 11 and 14.please advise.thank</p><p> s.v.premalal </p>
S.V, you should either use only power bipolar junction transistors or power mosfets. Don't mix up the two
Finally made it! Works perfectly!
Finally made it! Works perfectly!
<p>WHat if we use RC filter after pins 14 and 11 and then to mosfet so that we can get a SInewave output..we can convert square wave into sine wave using RC filter</p>
<p>test it out and post us your results.</p>
<p>yes I tested that but The MOSFET's are not responding to SIne wave signals,,,well we cant drive a MOSFET with AC signal....</p>

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