Make this 3 Phase Inverter Circuit

The post discuses the how to make a 3 phase inverter circuit which can be used in conjunction with any ordinary single phase square wave inverter circuit. The circuit was requested by one of the interested readers of this blog.

The Circuit Concept

A 3 phase load can be operated from a single phase inverter by employing the following explained circuit stages.

Basically the involved stages can be divided into three groups:

  • The PWM generator circuit
  • The 3 phase signal generator circuit
  • The mosfet driver circuit

The first diagram below shows the PWM generator stage, it may be understood with the following points:

The PWM Stage

The IC 4047 is wired as a standard flip flop output generator at the rate of the desired mains frequency set by VR1 and C1. The 555 IC is configured as a PWM generator which sets the RMS of the 4047 output to the required degree by chopping the output transistor base signals.

The dimensioned push-pull PWM now becomes available at the E/C junction of the two BC547 transistors.
This PWM is applied to the input of the 3 phase generator explained in the next section.

The following circuit shows a simple three phase generator circuit which converters the above input push-pull signal into 3 discrete outputs, phase shifted by 120 degrees.

These outputs are further bifurcated by individual push-pull stages made from a NPN/PNP transistor stages. These 3 discrete  120 degree phase shifted, push pull PWMs now become the feeding input signals (HIN, LIN) for the final 3 phase driver stage explained below.

This signal generator uses a single 12V supply and not a dual supply.

Complete explanation can be found in this 3 phase signal generator article

The circuit below shows a 3 phase inverter inverter circuit stage using H-bridge mosfets configuration which receives the phase shifted PWMs from the above stage and converts them into corresponding high voltage AC outputs for operating the connected 3 phase load, normally this would be a 3 phase motor.

The 330 high voltage across the indivdual mosfet drivers sections is obtained from any standard single phase inverter integrated across the shown mosfets drains for powering the desired 3 phase load.

Full-Bridge Circuit using 3 Half-Bridge Drivers


ISSUES FOUND IN THE ABOVE  3 phase inverter circuit design

The above circuits are not entirely correct and needed a few serious corrections.

After reassessing the circuits I have come up with the following revised diagrams of a 3-phase inverter circuit.

Presently it's a square wave type, I'll soon explain how it could be converted into a modified pure sine wave simply by inserting a dimesioned PWM input to the shut down pins of the half bridge driver ICs.

The ground rail of all the circuits should be terminated into a common line.

Improved PWM Stage


4047 3 phase Inverter Circuit


3 phase signal generator


In the above 3 phase generator circuit (second last diagram) using a sine wave doesn't make sense because the 4049 would ultimately convert it into square waves, and moreover the driver ICs in the last design employ digital ICs which will not respond to sine waves.

Therefore a better idea is to use a 3 phase square wave signal generator for feeding the last driver stage.

You may refer the article which explains how to make a 3 phase solar inverter circuit for understanding the 3 phase signal generator stage functioning and implementation details.

Simplifying the Above Designs

In the above explained 3-phase inverter circuit, the 3-phase generator stage looks unnecessarily complex, and therefore I decided to look for an alternative easier option for replacing this specific section.

After some searching I found the following interesting 3 phase generator circuit which looks pretty easy and and straightforward with its settings.

Therefore now you can simply replace the earlier explained IC 4047 and the opamp section entirely and integrate this design with HIN, LIN inputs f the 3 phase driver circuit.

But remember you will have to still use the N1----N6 gates between this new circuit and the full bridge driver circuit

100 thoughts on “Make this 3 Phase Inverter Circuit

  1. Have questions? Please feel free to post them through comments! Comments will be moderated and solved ASAP.
  2. Hi, I'm an electronics hobbyist, not a professional and I'm interested to this project.
    Can you explain me these things :

    1 – I want to know if the bridge driver, 4047 and opamp have the same ground connection ( 0v ) and so the negative supply is only to power the opamp.
    2 – Why a diode 1n4148 is used in the first circuit to stop the conduction of ground of the second BC547 (It switch only the ground in PWM?).

    3 – How are switched the Low Sides of the drivers (LIN) if the PNP transistors of the signal generator switches only the ground ? I know that a positive signal must be used to switch either the High and Low Sides of the driver, but with different waveform.
    4 – I saw in some schematics that using an half bridge that a doubled voltage supply is required. Now, must to use a 330V DC Supply or I need a doubled Voltage ?

  3. Hi, maybe the High Frequency PWM signal from the 555 can be applied (through the diodes) to the outputs of the Hex Buffers, so it can quickly turn on/off the square wave signals.

    • No, that would cause oppostie responses for the NOT gate inputs….it would be more correct to connect the diodes with the shut down pins of the half bridge driver ICs, in fact diodes won't be required, pin#3 of the 555 astable could be directly integrated with the shut down pins of the driver ICs.

  4. Hi i think this circuit will be good for me i would like use for 3 phase 400 volt asynchronus motor as generator for make induction in motor to generating electricity , my aim is from 12 DCvolt engine alternator who spin asynchronous motor convert to 12 v ac and with transformer make 400 v AC an this 400 ac to VDC I dont want use capacitors use between faces for that i would like electronic circuit i am little confuse thats pins SD where i should connect it ?

    • Hi, the above circuit is a 3 phase motor driver circuit from a single phase source… i cannot figure out how it would help your application.

      SD should connected to positive for normal operation, if it's connected to ground the whole IC freezes.

    No Voltage on Gate 3….Output 0 Voltage with No Frequency…

    On Gate 2- Voltage 6.56 with 50Hz
    On Gate 4- Voltage -6.70 with 50Hz…

    How can I solve This…..Advance Thnx

  6. With the value of a few component i'm lost:

    1). R1, P1 from the square wave generator?
    2). rectifier bridge used for the supply of the motor
    3). the driver transistors


    • 1) R1 and P1 will need to be determined by experimenting as per the desired output frequency.

      2) rectifier diode current will depend on the amp specs of the motor.

      3) you can use IRF840 for the mosfets.

    • Thank you Muhammad, the 555 IC stage is for inserting PWM into the inverter in order to make the waveforms modified sine waves,

      I did not include it in the revised diagram just to keep it simple, you can add it if you want across the HIN, LIN inputs of the driver IC.

  7. I am working on 3 phase inverter I have simulated above circuit in proteus.
    i gave sine wave as input to lm 324 accordingly i get 3 phase voltage but when this output i given to ic4049 i didnt get any output.

  8. Hello sir,
    in order to perform the three phase to 2 phase conversion by d-q transformation. then how it will be implemented in hardware. please do the needful. Can you provide me your email id??

    • Hello Neeta, I can't produce the calculation for the proposed circuit, since the design is a square wave inverter and the stages are all digital I don't think the dqo transformation would be relevant, even if it is so I have no idea how to do it for the presented design.
      my email can be found in the contact page, at the top

  9. Sir, If I need 3 phase inverter with 100Hz to the motor, how much the frequency input of my inverter?, I can imagine only if push pull inverter the input is 2X then output, isn't it?, thanks in advanced.

  10. Hello Sir,
    I was hoping to use this circuit power a 3phase 240vac motor from 12vdc. Will this circuit work for me? What sort of modifications will I need to make to change it from 330v to 240v?
    Thank you for this guide, Super helpful.

  11. sir, i'm making a three phase inverter. So far I have made a simple gate driver circuit and I can switch each individual IGBT perfectly. But while making three legs of the inverter how should I connect them. Should I use bootstrap capacitor?

    • Amit, you will have to make an ordinary single phase inverter, then rectify its 330V AC to 330V DC and use it with the full bridge circuit for getting the required three phase output….the 3 phase from the mosfet/IGBT bridge can be directly used for operating the 3 phase load

  12. Im extremely thankful to u for sharing this over internet.. This ws very helpful for me to do my studies.. I have few doubts regarding this. Is it possible to change the duty ratio and the switching frequency as per our requirement? If yes can u plz explain in simple words? Thankyou

    • It's my pleasure Pathmasiri, that looks like a beautiful and very simple to implement IC, I'll definitely introduce this chip in my website soon, through a new article.

      By the way you just have to apply an alternating 3 phase signal across the shown LIN HIN inputs of the IC, exactly as explained in the above article…..and you can get the results by directly connecting your motor across the shown outputs since it already incorporates built in mosfets.

    • Hello Bhavya, you can try the concept which is explained in the above article, for the 3 phase generator you can use the last circuit using 3 opamps…if you have any specific questions you can feel free to ask them through comments.

  13. sir pl provide your email id….i send my Doc file…
    Sir i have using op amp for compare to sine wave and triangular wave…and than gate pluse are in mosfet circuit….and than V/F ratio find and load is motor joint…
    so pl help me

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