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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Adhim3 days ago

Sir , can i use this circuit for 24V , 1000watt inverter.

muffrin4 days ago

hello mr nick i like your pwm inverter circuit an i already buy all the part an ready to build it but just one question can the 24v primary coil wind over the secondary coil or is it matter which coil wind first 24v on top the 220v coil or 220v on top please help me here

nickk (author)  muffrin4 days ago
usually the thick "24v" wire is always on top (outside). it doesn't matter which is on top but becuase of the thickness and not easy to handle make it as outer.

Hi Nick, I'm wondering what are your thoughts about this pure sine wave diagram?

Also, how could I connect just the driver from the above diagram to the power stage? Sorry not really good at electronics, just trying to learn by myself. Thank youuu

mohe16 days ago

hi can you submit me the complete circuits for the battery charging and i need to ask about the brigde and the transformer T1 in the driver schematic circuit , thanks

mohe16 days ago

hi can you submit me the complete circuits for the battery charging and i need to ask about the brigde and the transformer T1 in the driver schematic circuit , thanks

excuse me sir,, is it possible to supply desktop computer and airconditioning units if the frequency of our inverter is square wave and not pure sine wave? cause our prof is deciding that our inverter must supply a computer or aircondition unit.. thank you again sir.. i hope you will answer it..

chivindwe10 days ago

Some pictures. The aluminum plates are my make do heat sinks. I salvaged them from old huge hard drives. The fun is installed under the expanded wire. It is to push air up over the heat sink plates.

nickk (author)  chivindwe9 days ago

One other thing.. I already said in my notes#9 not to push air into the inverter, this will not work! Please read the notes carefuly they are there for a reason.

nickk (author)  chivindwe9 days ago

I like your cooling discs but they are not so practical for servicing the inverter, it will be difficult to test transistors that are at the bottom. Connection mistakes could easily hide between those disc layers. I don't know about air flow between the discs, the channels seem congested with wirings. Anyway thumbs up, it looks pretty heavy duty design !

chivindwe10 days ago

Thank you Nickk for the reply.

(A) I have checked the transformer by applying 220 volts from the mains supply. Its stepping down 220V to 33V. A little math show that actually it can work as 36V to 240V step up. That is OK for me.

(B)How much current will my 6KW inverter draw from the butteries when there is NO load applied to its 220V output?

(C)Is the feed back transformer (12V 0.5A) very important? Yes I did not connect it in my first test and I did not get satisfactory results but why is it necessary since we already have power from the 7812.

(D) My inverter is blowing some transistors when I connect the TIP 122 collectors to the transformer. It is however humming ok when I leave the collectors unconnected. I have not load tested yet.

Here are some pics

God bless you Nickk!

nickk (author)  chivindwe9 days ago

Hello chivindwe,

A) Since the transformer turned out 220/33, You should make tests using 3 batteries (3x12 = 36V) to see results.

b) around 1 Amp

c) This is a PWM circuit, it means it self stabilizes it's output to remain 220v at all times no matter if the charger is switched ON or OFF. I think you misunderstood this part here.. the 220/12v 0.5amp transformer DOES NOT GET CONNECTED to external power source, it gets connected to T2, see the diagram carefully. It acts as a feedback sensor.

d) This should not happen, I suggest you recheck your wirings, although the cooling discs are a nice idea but they are complicating the setup, wiring between the transistors can not be seen easily and clearly, Did you seperate the 2 disc banks from each other? Transistors and cooling discs from side A should be isolated from transistors and cooling discs of side B, They must not touch.

mr:nickk i have a problem i use battery 12v 7ah but it empty fast about 1min why


and the best battery charger circuit you have thank`s

shida3 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

Eng_MYM shida1 month ago

عزيزي .... الناس دي مش بتتكلم عربي ...
لكن أحب أقولك إن الموسفت اللي في الدائرة يستحمل لحد 200 IRFP250فولت ... يعني هي هي الدائرة لكن تغير بس الترانسفورمر 2 ...
بدل 12- 0 -12
و طبعا الخارج بتاعة زي ما إنت عاوز
ربنا يستر و يطلع كلامي صح ....ههههههههههههه

فعلا كلامك صح eng_mym

qasim123411 days ago

Hello Nick,

I made your inverter circuit successfully, thx a lot :). Now I need our urgent help because I am stuck up in the overload protection part.the relay isnt switching at all. the inverter part is working fine. I am using a 8 amp(dc) transformer, and was running a 85Watt load. I used bc547 and 3K pot instead of 2.2K. Please help. Thx.

is it possble to produce a pure sine wave if i use a bubba oscillator with this circuit? thank you... =)

excuse me sir,, is it possible to supply desktop computer and airconditioning units if the frequency of our inverter is square wave and not pure sine wave? cause our prof is deciding that our inverter must supply a computer or aircondition unit.. thank you again sir.. i hope you will answer it..

is it possible if the battery is 24v 60ah and we will make a parallel of 4 battery so that we can come up with a 24v 240ah and the output is 5000watts for the inverter?

nickk (author)  dingkoi.magdoza16 days ago

this is not a recommended setup, if one of the batteries is weak the energy of the other batteries will leak through it. even for charging this is not good.

chivindwe16 days ago

Hi Nickk. Thank you for everything. I am working on a 6000W inverter! I have connected 24 pairs of Motorola 2N6277 transistor. Unfortunately for me my transformer is rated 220V to 54V. So I cant push in 84V. It was a step down transformer for charging telecommunications butteries and it used charge a huge bank at MORE than 100 A easily. I am now using it as a 48V/220V step up. The trouble is:

1. How much current should I anticipate in the primary before any load on the 220v output? I know that at full load it will drain at least 125A in the 48v input. I am sure my transformer can handle this current.

2. Why is my driver circuit only driving one bank of the transistors even when I am getting clean square waves on the oscilloscope from the emitters of both the TIP 122 transistors. I have double checked the transformer. Its Ok. Swapping the banks is shows that only one bank on the same TIP 122 is being fired.

3. The same TIP 122 transistors are allowing the square wave through from from the base to their emitters even before I connect their collectors to the transform. Is that the correct behaviour of these transistors?

4. I am getting about 3.5V on points 1 and 2 instead of 2.5V. Approximately what voltage should I expect from the emitters of the TIP 122 transistors relative to ground?

5. Why is it that adjusting R1 variable resistor does not seem to affect the oscillator chips (SG3524 A) output on lead 11 and 14?

Thank you Nickk for everything.

nickk (author)  chivindwe16 days ago

Hi chivindwe,

As a start using a 54v transformer with 48v DC supply will not give you 220v at all.

You'll get a mav of 195v at the output of your 220. Unfortunately you can't use this transformer.

1) I didn't understand what you mean.

2) The driver acts as a push pull where on each half cycle of the 50Hz one of the channel banks should "MUST" fire up. To get a better reading disconnect the transformer and re-test, both channels must be oscillating as a push-pull. They will never be ON together at the same time. This gets synchronized from within the SG3523 itself.

3) Yes, but connect the collectros or they'll get hot on any load.

4) It depends if your multimeter is set to DC or AC (That's why you either see it 2.5 or 3.5). At the emitters of the 122's you should get a a full 8v if you used 7808 as a regulator, if you installed a 7812 you should see a 12v. it is relative to the regulator.

5) Is the feedback 0.50amp transformer installed? Did you load your inverter with some load like 50 watts so u get accurate calibration.

Upload some photos please, lets see what you're doing over there.

Welcome, my pleasure.

Hi Sir Nick - I hope you're having a great day! First of all, let me extend my heartfelt thanks to you! I am extremely amazed that you're giving out a schematic diagram as wonderful as this, so thank you so much! -- Anyway, I am in process of building this circuit though my knowledge on electronics is too slim -- My dad's helping me out to finish this project since he has solid background on electronics. I've couple of questions for you, your reply will be highly appreciated.

(a) We're trying to integrate the 'Pure Sine Wave' driver that you have in this link (bit.tly/1zQvCsT) to the "Power Driver" of this PWM DC/AC 220v Power Inverter --

We bought 8pcs of 2N3773 to come up with 500watts power. My question related to this are

(a.1) is it OK to have 500watts of transistors and 500watts of T2 Transformer without allowance? Or shall I lower down the wattage of my transistors?

(a.b) Is it OK to connect the Pure Sine Wave driver you showed in bit.tly/1zQvCsT to the Power Driver of the diagram above (250 to 5000 watts PWM DC/AC 220V Power Inverter)? We want to have at least 500watts of Pure Sine Wave inverter, I'm thinking if there's a need to adjust anything on the Pure Sine Wave driver in bit.tly/1zQvCsT ...

(b) May we have the values of the D1 and D2 in the Power Driver above?

(c) Are there any alternatives for 2.2uF/400volts in the filter? Unfortunately we had a hard time looking for one earlier :(

Your help will be greatly appreciated. Again, thanks Nick!

nickk (author)  arist.aquino23 days ago

Hi arist.aquino,

Frankly I don't recommend that you build the Pure sine wave inverter, it has a very basic code which isn't perfect, although you'll see a pure sinewave on the oscilloscope but when you apply a load all sorts of weird problems start to show.

I highly recommend that you build this one here based on the sg3524 chip, this is a heavy duty design that has been tweaked over time for perfection, you'll be amazed of it's performance and durability.

a1: no problem with the number of transistors, adding more does not affect T2 in anyway.

a2: yes can be done.

b: those are general purpose 6amp diodes, don't install them if not available, they don't affect performance.

c: unfortunately you MUST put the 2.2 or you'll not see pure sinewave.

Regards to your dad.


(removed by author or community request)
nickk (author)  arist.aquino23 days ago
Hello arist.aquino,
Yes a 42-Amps rating is correct for 500w. You'll be able to load a 500w only which is the max rating of your transformer.
baldrin12324 days ago
(removed by author or community request)

use a battery or if you have ATX power supply you can use it for testing your project.

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?

nickk (author)  Md Nasir Ahmmed Patoary24 days ago

Any equivalent should work, check equivalent tables.

dessi made it!2 months ago

thanks nick

nickk (author)  dessi24 days ago

Thanks for the pics, very nice well put together design !

dessi2 months ago

hi nickk i made it twice and it works very well

nickk (author)  dessi24 days ago

:) nice

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
nickk (author)  PinheiroPedro24 days ago

2.5A is useless.

gmilic1 month ago

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

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