Making a 200 watt Compact PWM Inverter Circuit – Using Tiny Ferrite Transformer

This circuit was requested by a few of the dedicated followers of this blog, namely Mr. Rashid, Mr, Sandeep and also by a few more readers. Initially I could not figure out the concept behind these compact inverters which completely eliminated the bulky iron core transformers. However after some thinking it seems I have succeeded in discovering the very simple principle associated with the functioning of such inverters.

Lately the Chinese compact type inverters have become pretty famous just because of their compact and sleek sizes which make them outstandingly light weight and yet hugely efficient with their power output specs.

Initially I thought the concept to be unfeasible, because according to me the use of tiny ferrite transformers for low frequency inverter application appeared highly impossible.

Inverters for domestic use requires 50/60 Hz and for implementing ferrite transformer we would require very high frequencies, so the idea looked highly complicated.

However after some thinking I was amazed and happy to discover a simple idea for implementing the design. Its all about converting the battery voltage to 220 or 120 mains voltage at very high frequency, and switching the output to 50/60 HZ using an push-pull mosfet stage.

Looking at the figure we can simply witness and figure out the whole idea. Here the battery voltage is first converted to high frequency PWM pulses. These pulses are dumped into a step up ferrite transformer having the required appropriate rating. The pulses are applied using a mosfet so that the battery current can be utilized optimally.

The ferrite transformer steps up the voltage to 220V at it output. However since this voltage has a frequency of around 60 to 100kHz, cannot be directly used for operating the domestic appliances and therefore needs further processing.

In the next step this voltage is rectified, filtered and converted to 220V DC. This high voltage DC is finally switched to 50 Hz frequency so that it may be used for operating the household appliances.

Kindly note that though the circuit has been exclusively designed by me, it hasn’t been tested practically, make it at your own risk and on;y if you have sufficient confidence over the given explanations.

Parts List for 12V DC to 220V AC compact ferrite core inverter circuit.

R3—R6 = 470 Ohms
R9, R10 = 10K,
R1,R2,C1,C2 = calculate to generate 100kHz freq.
R7,R8 = 27K
C3, C4 = 0.47uF
T1—-T4 = BC547,
T5 = any 30V 20Amp N-channel mosfet,
T6, T7 = any, 400V, 3 amp mosfet.
Diodes = fast recovery, high speed type.
TR1 = primary, 13V, 10amp, secondary = 250-0-250, 3amp. E-core ferrite transformer….ask an expert winder and transformer designer for help.

An improved version of the above design is shown below. The output stage here is optimized for better response and more power.

74 Replies to “Making a 200 watt Compact PWM Inverter Circuit – Using Tiny Ferrite Transformer”

  1. hi mr. swagatam can this inverter be modified?
    great job on cracking this secret, once i opened one of these light weight modified inverter and tried to understand its function so it might be similar configuration as this one. congrats!! and


  2. hello sir…
    its rally a very nice one..i saw may inverter circuits in ur blog. i could find changes in implementing the new one from the old interver circuit in ur blog. sir, i want to make an inverter. what are the considerations we need to take??! as per my knowledge i think we should first make a plan about the things we need to use wen the power is lost (i.e., light, fans, chargers etc..) and the power consumed by them. so according to the charging capacity of inverter these things can b used.. right sir??

    1. Thanks siree,
      Yes you are very much correct….planning-out before making any project is very important, inverters especially require strict planning before configuring….rightly said.


  3. hello sir..
    if we need to make an inverter for 3fans and lights then what wil the specifiacations sir??
    can we make inverter for running a.c ?? is it tooo difficult???
    what is the idea and concepts used in making inverter for our specifications?? plz tell me sir

    1. It will require a perfectly optimized transformer, because transformer is the heart of an inverter, rest all can be calculated by standard means….if transformer is properly designed then rest of the things won't be much difficult.

  4. Hi. Mr swagatam can you post how calculate the rc to change the frequency. Im having trouble figuring out the correct formula for your disign.
    Thanks for your time…


    1. Hi Mr.Roger,

      You can use the following formula for finding the frequency or RC:

      f=1/1.38RC, where R and C are the values of the transistor base resistor and capacitor.
      f is in Hz, R in Ohms and C in Farads.

  5. hii swagatam this is kurush karanjia here . This circuit can be very useful for me in designing the type of PCU for solar application i am trying to design. I will be very thankful if you help me to design this circuit for 1kw and above

    1. Hi, Khurush,

      Again this circuit is also based on theoretical assumptions, it has not has been tested practically.
      i think if the transformer is wound correctly, this circuit might start working instantly.

      The concept needs to be tested and applied practically over a smaller design first.

    1. You can use the following formula for finding the frequency or RC values:

      f=1/1.38RC, where R and C are the values of the transistor base resistor and capacitor.

      f is in Hz, R in Ohms and C in FARADS.

    1. for testing TR2 can be a 12-0-12v 5 amp transformer. Initially do not connect the output of TR2 to the grid, first check whether the output is producing the required AC or not…..

  6. Dear Mr. Swagatam,

    Warm Regards and Complements to you for your efforts and service to people like me.

    I've designed a complete system that involves use of some electronics for a revolutionary improvement in mileage of Gasoline powered engines. I've already designed the other components and presently require an inverter circuit that takes in 12 – 15 Volts and gives out 220 – 250 Volts out (50/60Hz). The load is around 100 Watts but to be on the safer side I need 150 Watts. On top of this, the circuit has to be small in size. This design seems to be very right for the purpose but I'm not an "Electroincs" person hence I need your help regarding this. Can you provide me with the Circuit Diagram, PCB Layout & Component List (Part Nos.). I've learned to etch the PCB using Ferric Cloride.

    Thanking you in anticipation and looking forward to your response.


    1. Thanks Unknown,

      The above circuit is in its most crude form so I won't recommend this circuit to you, moreover optimizing the ferrite transformer winding would be difficult for any newcomer.

      You can go for any iron core type transformer inverter, it may be a little bulky but will be a lot easier to build and will provide with 100% results.

      The easiest one in this blog can be witnessed here:

      Though the title confirms a 50 watt output, it can be suitably upgraded to 150 wats by moifying the transformer and the battery.

      Regards, and Best wishes for the project

    2. Thank you so much Mr. Swagatam!

      You just kick-started my stalled project. I'll look to the diagram you've mentioned and would try making it at earliest possible. All other components are working fine and I was using a 600 VA UPS instead of inverter circuit. As I've told you that I'm not an electronics person hence I needed somebody who is an expert and in my humble opinion – you are one!

      I'd request you to pass on the exact details of the desired transformer.

      I'll soon be getting in touch with you (if you don't mind – personally!)

      Thanks again for your good wishes.


    3. Thank you unknown!

      You may use an ordinary 9-0-9v/15amp secondary, 220V primary, step down transformer for the application, kindly note that the suggested circuit is a square wave design so you shouldn't operate anything sophisticated at its output.


  7. Thank you so much Mr. Swagatam,

    I'm assembling the inverter today though I've to source the components from a distance of 40 kms because I live in a remote area. And actually my requirement is square wave only. When I used a normal UPS with modified sine wave output, the results weren't as expected but when I used a "Desi" inverter with square wave, the results were good. Actually there's very little sophisticated electronics involved after the step up. this square wave output goes to High Tension Ignition coil (1:100).

    And I must share the results of my initial tests with you because you just solved one of my problems. With this system on, the test bike (100 cc) is giving me more than 160 kmpl without any apparent loss in power or any sign of engine wear & tear! I'm still improving on the design to go even farther!!

    Thank you so much once again for helping me "Miniaturizing" the electronic part of my system.


    1. Gosh!!, now I understood what you are trying to make.

      You are perhaps trying to make an electronic ignition system which would operate independently, without using the alternator voltage…right?

      I had made this circuit some 7 years ago while designing a button start ignition system for 3-whelers, the ignition system fired wonderfully but the mission failed because the operation required sucking-in of petrol in the ignition chamber, which involved mechanical operations….with no help around I had to drop the idea.

      Since your load is just an ignition coil, a simple 9-0-9/ 1amp transformer would do the job…no need of using a 15 amp transformer as suggested by me in the earlier comment…..I hope you are involving a CDI unit also for enhancing the results??


  8. YOU ARE ABSOLUTELY RIGHT there Mr. Swagatam…! You're a veteran in this…
    My system is made up of what you guessed correctly plus a replacement for carburettor. And I've already tested it… Its working good. All I wanted was to make a smaller circuit that can be fitted onto bikes. As far as cars are concerned, the size of the circuit can be ignored. The make/brake operation is being handled by the CDI unit, ignition coil is doing its own work plus I add a pulse of high voltage to it. The spark is wonderful, jumps a gap of 5mm and its size is around 15 mm in diameter. The spark is so strong that it burns even a very weak mixture of air and fuel (I've achieved 50:1 ratio and I'm planning to increase it to around 80:1)
    I'll keep you posted about it. After all, you're my partner in development now… :-D.


    P. S.: My test bike (a CD 100 Deluxe) is running this system and is giving me between 160 and 210 kilometers per litre depending on driving dynamics!

    1. Dear Mr. Swagatam, Please let me know about the wattage of Resistors in the given circuit… Also, When I try to simulate your circuit in Circuit Wizard, the output is very choppy. CW doesn't have SK1058 in its library so which else can I choose to get the simulation right?

  9. Hi
    Mr: Swagatam How are you Hope you Fit and Fine There
    my dear can you tell us the which mosfet p channel available to 400/500 voltage
    N channel is available to high voltage but P channel ???????Kindly reply
    Thanks bye

  10. hello everyone !
    i m trying to make a 200W single phase modified sine inverter. but i have to use boost in order to achieve so! (its required :)) …
    what i m trying to do is to boost a 12v dc battery to 315v dc, then feed that 315vdc after removing the ripples to an inverter circuit.

    i need guidance of u all … in lue of power ratings, power compensation, specifically inductances and any other advice u guys might find useful.

  11. Hi Swagatam,

    I am working on a design project to develop a circuit that converts 250V DC to AC voltage. The circuit has to meet the following requirements,

    – Input voltage and current = 250V DC and 20A
    – Output voltage and current = Pure sine wave AC (250V minus voltage drop) and 20A
    – Maintain pure sine wave output like utility power over the entire load range (0 to 20A) for all types of load.
    – Operate continuously
    – Minimize power loss between input and output
    – Minimize waste heat
    – Smallest possible size

    Please I need your help in drawing the circuit diagram to meet these requirements above, also please give me a list of the components required for this circuit. I will very much appreciate all your help in this matter. Thank you very much for your time and help.

    1. Hi, you can fix them by some trial and error, initially use 27K for the base for the resistors, 2k2 for the collector, and 0.47uF for the capacitors, measure the frequency for this set up and then you can evaluate the other appropriate values for other desired frequencies using cross multiplication

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