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.

hi nick please send me .detailed matter regarding design of this ckt

ptiuliutinas made it!5 days ago

Works well. I used 3 pairs of 2N3055 (they're cheapest) and ~100W 10-0-10V transformer for now.

ymashood8 days ago
Please I need information on how to desine. Transformer for an inverter. Eg. The turns of the winding including the size of the guage to use

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.

twyeth15 days ago

hi nickk

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

belal_saad118 days ago

could you please send us the battery charger circuit for both 12 vdc and 24 vdc???

thanks in advance

HADHYA23 days ago

hello nickk can you kindly guide me for the necessary changes to be made for the following requirements


Inverter shall be suitably rated for
driving 110VAC (+/-10%) Frequency 50Hz (+/-3%) single phase motor of 150Watts
(1.37Amp). InputDC 72V (+/-25%)There may be a
momentary voltage fluctuation from 60V to 95Vdc during sudden loading and
unloading of another high amp. Motor; ensure that during this fluctuation
inverter should not trip.

Inverter should be with the following

  • Short circuit protection
  • over load protection
  • thermal protection

The switching devices should be only IGBT
or MOSFET type


Himadri Adhya

animeshmani1 month ago

how i can charging the battery autometicly in this inverter ckt.?pls .pls send me battery charging

ssrivastava11 made it!1 month ago

Did the circuit on a General purpose pcb. works fine :)


the best part is the feedback, its able to regulate the voltage at 86% duty cycle according to my experimental setup.

I will modify the system using boost converter from the solar panels according to my specification.

thanks @nickk for sharing the inverter circuit design :)


I would like to design an inverter circuit of 200W using 2 solar panels of 75watts and 16.4V in series, what should be the modification done in the above circuit to obtain my desired circuit

I am also working with solar panels ryt now. I would suggest to bring down the voltage to 12 Volts through dc to dc regulator. I am emphasizing on bringing down voltage to standard value coz the radiation intensity on sun may vary which can cause some up and down of voltage so dc to dc voltage regulator will help you give a perfect 12 volt supply to your transformer and the circuit. and rest all you follow the same circuit diagram as given by nick. it works fine..!!

safeermaher1 month ago

Hi, it is Micheal
I saw your design in here and i thought about trying it and fortunately i found your circuit already made in the market so i bought it ;)
but after connecting it with transformer (50 Amps) and d313 and tip35 transistors i got low voltage "around 160v" and the low voltage alarm was already built in that circuit and it always keeps toning for no reason!!!

can you please help me.. i tried to set the voltage to the higher and the frequency as well but the voltage didnt exceed 170v i added few capacitors at the output so i get 200v but it drops down to 170 when loaded with 100w lamp

i've uploaded a pic.. please check it

please any advise.. thank you very much

nickk (author)  safeermaher1 month ago
d313 and tip35??
where do you see those in my schematic?


thank you for your note about the transistors..

i replaced them with tip122 and 2n3773 transistors

but i still have low voltage...

can i change the windings of my TS to 9-0-9 ? do you think that this can solve the problem?

and one more question please.. what can i do regarding the voltage decrease while connecting the load?

nickk (author)  safeermaher1 month ago

1- does your 12v battery drop below 12v when the inverter is on ?

2- did you set the frequency 50Hz?

3- did you regulate with R1 to get the voltage to 220v ?

4- if you checked all the above and still your 220v drops, try to set the frequency to 60Hz

5- send us feedback

do you think that replacing the TS with a 9-0-9 one can solve the problem??

nickk (author)  safeermaher1 month ago

this design calls for a 12-0-12 transformer to work properly, instead of changing the ts value you should search where your problem is.

  1. what is voltage reading on the primary side of T2 ? if it is not 12v-0-12v AC then you should do the following:
  2. replace the 7808 regulator with 7812
  3. what became the voltage reading on the primary side of T2 after replacing the regulator.?
  4. If the above doesn't work, disconnect the trans from the circuit and connect THE SECONDARY side to a 220v AC source outlet and test the primary side with a voltmeter, what voltage are you getting ? is your 220v exactly 220 or less ?

Dear Nick

I already changed the windings of TS to 9-0-9 and i will make what you said with an other TS and other circuit and let you know about what happened with it.

the previous windings was exactly 13v output because it is tested before

any way.. now i am having about 250v output without load.. when loaded with 100w lamp the voltage become 202v

now if about 10 mins and while the battery is becoming the lower voltage the output keeps going down.

can you help me to make the output voltage steady??

nickk (author)  safeermaher1 month ago

you will not be able to make the output steady unless you stick to the original design of the circuit. the only change that you're allowed to make is to change the 7808 to 7812. it seems your problem is with the transformer, you must use an exact 12-0-12 / 220 trans. (The trans. must be tested properly to insure these voltages) using a 9-0-9 transformer is not a good idea, it will burn soon.

Dear Nick
Ok.. i will change the TS to 12-0-12 though it wasn't working in the past and it was tested

i will apply your new changes to the circuit and change the TS and let you know about it..

Thank you for your help

once i read the voltage on the primary side and it was about 9.5v-0-9.5v

nickk (author)  safeermaher1 month ago

9.5 is not good. it should be 12v

once i read the voltage on the primary side and it was about 9.5v-0-9.5v

Dear nick..

thank you for your quick replies.. :)

about your questions:

1- i tried two batteries.. one of then doesn't drop below 12 while the other drops to 11.7v but both of the battery are doing great with commercial normal inverter 1000w

2- the frequency was already set to 50hz when i bought it.. but it didnt work well

3- i regulated the R1 to maximum that what caused in that time about 10v raise.

4- i also set the R2 to maximum i got a naughty sound from the transformer in this case, but any way the voltage still low..

i even tried an other TS made by other manufacturer and i still have the same problem..

kindly awaiting for your replay :)

about the old d313 and tip35 they was advised by the one who made the circuit ;-)

hey Nick nice work

I need some of your advice..!!
I am planning to make 2kVA inverter for my solar panels.
I have 250 watt 4 solar panel.
The Voltage rating of each panel at full load is 37.15 volts
The Current rating of each panel is 6.73 amps.
On the AC side I have a load of a water pump (0.5~1 hp) + 200 watt load.
My teachers told me to go for series connection for the solar panel since high voltage is easy to handle than high current.
I don't have any battery system in my Inverter setup just the dc supply is given by solar panels.

I would like your opinion and suggestions about it.

nickk (author)  ssrivastava111 month ago

This inverter needs a fixed constant DC source with a high amperage to work properly on heavy loads, this only means batteries. For every 1 ampere required at the 220v side you'll be draining like 8 to 10 Amps from the DC side. I don't think that connecting it directly to solar panels is a good idea. Theoraticaly you can do some changes to the circuit to make it work directly on your pannels but don't expect to get more than 250 watts of power which makes it useless.

if possible can you give me your mail ID

Actually i have 4 solar panels .. total power will be 1kw
since we have a water pump load which on starting can cause a lot of inrush current we are making a 2kw inverter system. I have seen in many places where a solar panel is directly connected to inverter & to the load side like water pump.

actually I am making a solar Inverter for a project so I have a lots of doubt.

According to your transformer winding recommendation for 2250 watt 36VDC P:72V "36-0-36" / S:220V transformer to be used. if I connect all the 4 panels in parallel i will be getting around 26 amps on dc Side on full load.

Is there any possible way to reduce the current required on dc side when there is a load on ac side..??

chukzy37001 month ago
Hello Mr. Nickk. Please I want to know the voltage of the Electrolytic Capacitors used: 220uf, 1uf, 10uf, 4700uf and 47uf. Please what is there voltage.. I hope to hear from you soon. Thanks..
nickk (author)  chukzy37001 month ago
50v should be ok
Jawaaz3 months ago
Hello Nick,
I have made the design you have posted and I was successful in getting a oscillating output from emitter A and emitter B from SG3524.I build a test power stage using a single pair of IRFZ44N mosfets for negative and positive half cycles respectively and used a 12-0-12 .5A small transformer for it.I have the following problem:
WHen I connect the transformer to the supply,The primary reads 24VAC across as it should be but the secondary reads only 145VAC..I also checked the transformer at 220VAC output and it gave me exactly 24VAC on primary,so I am puzzled why I am getting 145VAC when primary is 24VAC,Is there any problem in flux generation for square wave signal???I am scratching my head..
nickk (author)  Jawaaz3 months ago
Hello Jawaaz,
Please upload a photo of your setup.
Jawaaz nickk3 months ago
HEllo Mr. Nick,
Well I have rectified my problem now,actually I was only getting 32hz of frequency and at that frequency ,the induction process fails and cannot transfer all of the potential to the secondary coil,so I increased the frequency to about 60hz and the voltage on secondary coil got increased to optimum level...I guess in a transformer,the voltage on output side is directly proportional to the frequency of the potential on primary side...SO FOR ALL THE PEOPLE WHO ARE GETTING LESS OUTPUT VOLTAGE ON SECONDARY SIDE,TRY TO INCREASE THE FREQUENCY FROM 50HZ TO 60HZ AND RECHECK YOUR SECONDARY VOLTAGE AFTER THAT...
josfemi Jawaaz1 month ago

i have never experience this before, if i increase my frequency my output voltage remain the same and if i decrease my out put voltage still remain the same

nickk (author)  Jawaaz1 month ago

Thanks for this clarification.

reach2beelal2 months ago
Hi nickk,

Plz i need ur clarification can i wind my inverter transformer to 310v at d output and brings it back to 220v using feedback to avoid voltagedrop at the output

Plz what do i do to improve ur circuit so that pin10 should dectate low battery and shutdown
nickk (author)  reach2beelal1 month ago

no it doesn't work this way. the 220v will not drop unless the battery starts to get empty, when this happens nothing will bring your 220 back.

Hi nickk

What I mean is when I wound my transformer to 12v input and 230v output. When a connect the transformer and start d inverter it gives me 230v at the output BUT when I connect load at the output the voltage drops to less than the voltage without the load. The more I add the load the more voltage drops SO WHAT'S IS THE PROBLEM

That is why Isaid if during winding I increased the number of turn is the secondary to reach may be 300v and the used ur circuit to brings it down to 220v CAN THE INVERTER WORK FINE

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