Feb 12, 2012

How to Build a100 Watt, Pure Sine Wave Inverter Circuit

The circuit provided in this article shows you a simple way of building a useful liitle inverter that's easy to build and yet provides the features of a pure sine wave inverter. The circuit can be easily modified for getting higher outputs.

Let’s begin the discussion about how to build a 120 Volt, 100 watt sine wave inverter, by first learning it’s circuit functioning details:

The circuit can be basically divided in to two stages viz: the oscillator stage and the power output stage.

Oscillator Stage:

Please refer the detailed explanation about this stage in this article.

The power output stage:

Looking at the circuit diagram we can see that the entire configuration is fundamentally made up of three sections.

The input stage consisting of T1 and T2 form a discrete differential amplifier, responsible for boosting the low amplitude input signal from the sine generator.

The driver stage consists of T4 as the main component whose collector is connected to the emitter of T3.

The configuration quite replicates an adjustable zener diode and is used for settling the quiescent current of the circuit.

A full fledged output stage comprising Darlington transistors T7 and T8 forms the final stage of the circuit after the driver stage.

The above three stages are integrated with each other to form a perfect high power sine wave inverter circuit.

The best feature of the circuit is its high input impedance, around 100K which helps to keep the input sine waveform shape intact and distortion free.

The design is pretty straightforward and will not pose any problems if built correctly as per the circuit diagram and the provided instructions.

Battery Power

As we all know that the biggest drawback with sine wave inverters is its RED HOT output devices, which drastically reduces the over all efficiency of the system.
This can be avoided by increasing the input battery voltage up to the maximum possible tolerable limits of the devices.

This will help to reduce the current requirements of the circuit and thus help to keep the devices cooler. The approach will also help to increase the efficiency of the system.

Here, the voltage can be increased up to 48 volts plus/minus by connecting eight small sized 12 volt batteries in series as shown in the figure.

The batteries can be 12 V, 7 AH type each and may be tied in series for getting the required supply for the inverter circuit.

The TRANSFORMER is a made to order type, with an input winding of 48 – 0 – 48 V, 3 Amps, output is 120V, 1 Amp.

Once this is done, you can rest assured of a clean, hassle free pure sine wave output that may be used for powering ANY electrical gadget, even your computer.

Adjusting the Preset

The preset P1 may be used to optimize the sine waveform at the output and also to increase the output power to optimal levels.

Another power output stage is shown below using MOSFETs, which may be used in conjunction with the above discussed sine generator circuit for making a 150 watts high power pure sine wave inverter.

Parts List

R1 = 100K

R2 = 100K

R3 = 2K

R4,5,6,7 = 33 E

R8 = 3K3,


R10,11,12,13 = 1K2,
R14,15 = 470E,

R16 = 3K3,

R17 = 470E,

R18,19,21,24 = 12E,

R22 = 220, 5 WATT

R20,25 = 220E,

R23 = 56E, 5 WATTS

R26 = 5E6, ½ WATT

C1 = 2.2uF, PPC,

C2 = 1n,
C3 = 330pF,

C6 = 0.1uF, mkt,

T1 = BC547B 2nos. matched pair

T2 = BC557B 2nos. matched pair

T3 = BC557B,

T4 = BC547B,

T7,9 = TIP32,

T5,6,8 = TIP31,

T10 = IRF9540,

T11 = IRF540,

Oscillator Parts List

R1 = 14K3 (12K1),

R2, R3, R4, R7, R8 = 1K,

R5, R6 = 2K2 (1K9),

R9 = 20K

C1, C2 = 1µF, TANT.


IC = 324

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  1. hi mr swagatam how many fets on each side i need to get 1200 watts and how can i calculate the gate resistor to getting the desire power?


    1. Hi Roger.

      four on each side might do the job, but I'm not very sure, the gate resistor can be selected as 100 Ohms, you cannot calculate gate resistors of fets because they have no relation with current gain across the source/drain pins, they are placed just to restrict oscillations inside the fets.


    2. so how can i tell how many power the drain is going to give me?


    3. multiply the max current of the combined mosfets with the supply voltage...

    4. ok, wich side is the source on T11 "is it coming from negative - bank?


  2. were does T10 get its source from ? cant tell thanks.


    1. T10 source is from battery positive and T11 is from battery negative.

    2. what is my primary winding going to be for this inverter?


    3. 100 watts rated, cannot say about the number of winding or other details.

    4. i meant the transformer is it going to be a 0-24v primary?


    5. Yes it must be a 0-24volts input winding.

  3. hi mr swagatam im planning to build a SMPS -35/+35 dc/dc push pull converter with IC SG3525 with a rate power of 450watt for this pure sine inverter, so my concern is if it will work properly to drive the inverter? "so now will i need a 0-35v primary"


    1. Hi Roger,

      I cannot understand the use of an SMPS for driving an inverter.

      Because the smps would require mains AC voltage input, and the inverter would again produce the same AC mains at its output via the smps, so what's the point?

      Kindly first explain me this.


    2. im trying to raise the voltage like if it was a power amplifier just the same way as putting two 24vdc batteries in series! Regards.

    3. so you are doing it only for testing the above circuit?

      That means you would finally use batteries for the inverter after you confirm the results using an Ac to DC power supply first, right?

      I would recommend you the inverter circuit presented below, which is much simpler:



  4. Hello Swagatham,
    First of all thanks for sharing knowledge, i made several ckts from your blog and i'm happy with the output.
    Now, i have my computer UPS 500W with battery dead condition. I bought a new 12V 35AH battery as repalcement of old 12V 7.2AH one. I thought this should work for more backup time. I checked the charge current it shown ~10A.
    I run the UPS with 35AH battery, but the transistor getting very hot and the battery wires too even without any load. I measured the volt its 230V.
    I need your suggestion please,
    1. Is it Ok to use 32AH battery on computer UPS (600W) ?
    2. Should i do any modification ?

    Kind regards,
    Ram Sankar.V

    1. Hello Ram Shankar,

      Thanks and Welcome to my blog!

      Current is irrelevant as long as voltage is correctly matched.

      As rightly assumed by you, increasing battery AH should have increased the back up time without affecting the performance of the UPS.

      There's definitely something wrong with your UPS, and since it's consuming battery power without connecting any load proves that it's not functioning properly and needs to be repaired or replaced.


  5. nice tutorial :))

    i want to know what elimination require to make 1000 watt inverter

    1. thanks!

      add more mosfets in parallel and use a higher rated transformer and battery.

  6. What can use a mini generator AC 6V for input sine wave it?

  7. Dear Sir,
    i have a old ups double battery, its .7vA, can i use it as inverter or i have to make any modifications

    1. Dear Gowhar,

      An UPS is actually an inverter, so you can use it in the form of an inverter without doing any modifications, just make sure you do not load the output above the rated specs of the transformer.

  8. i have an old ups double battery, can i convert it into an inverter, if yes, how

  9. sir please where is the circuit to feed the second circuit i cant fined it or can you please provide full circuit of it? thank you.

    1. It'll be from a sine generator or a pwm generator as shown in the 1kva inverter circuit.

  10. hello sir.,
    i want to design pure sine wave inverter with help of TM4C123G and 4 MOSFETs..please tell me code for regarding this either for IAR or energia..and also please provide me any sites about the complete design of an pure sine wave inverter..
    thanking you sir!

    1. hello Naresh,
      presently i do not have the data for this design application, if I find it will revert to you with the info.

  11. Hi Swagatam, if I use 2 batteries(12V each) instaed of 8, will the rest of hte circuit diagram be the same? Do I need to change of the value of any components? Where do I connect my transformer exactly? And also are the 2 circuit diagrams in this link both same? I can't understand the first one(green coulour) properly, would have been great if u provided a clear picture if u have with u.Waiting for your reply

    1. Hi Jamey, you can try the last circuit given in the following article, it's much simpler:


    2. And also I can't exactly understand what kind of resistors 5E6, ½ WATT/ 220, 5 WATT
      are? In capacitors, what does 2.2uF, PPC / 0.1uF, mkt / 2µF, TANT mean?

    3. 5E6 = 5.6 ohms
      PPC = polypropelene
      MKT = metallized polyester
      tat = tantalum

  12. I'll stick to the 2nd circuit diagram. But do I have to change any other components or thir value if I use 2 12v batteries?

    1. for two 12v supply you don't have to change anything in the circuit, everything will be as given.

  13. sir, i have to make inverter using 75ah batterx for my incubator and the load is taken by my incubator is 70watts heating element so i need circuit for inverter pls help

    1. Pradeep, you can simply make the following circuit, use a 150 watt transformer for the application


  14. Hi sir,
    I have constructed the second circuit using Multisim but the simulation gives a distorted sine wave and the output current is very very low. Can you suggest what modifications be made to increase the output current. also, I dont understand the function of the second variable resistor in the circuit.

    1. Hi Venkat, It can be difficult to understand how the simulator may be assessing the circuit because there are any sages in the circuit with complex functionality.

      moreover the output waveform will depnd on the performance of the input sine wave which should be less than 1V peak to peak.

      there's only one variable resistor in the form of P1, it's for adjusting the quiescent current of the circuit.....keeping the input of the circuit short circuited and with no transformer at the output adjust P1 such that the the circuit consumes not more than 50mA

  15. Hi sir,
    I built the circuit in multisim and the results are not matching. The current output is very low and I am unable to figure out the fault or the necessary rectification. Also, I dont understand the functionality of the second potentiometer. Please help me with the same.