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Single Phase Variable Frequency Drive VFD Circuit

Single Phase Variable Frequency Drive VFD Circuit

The post discusses a single phase variable frequency drive circuit or a VFD circuit for controlling AC motor sped without affecting their operational specifications.

What is a VFD

Motors and other similar inductive loads specifically do not "like" operating with frequencies that might be not within their manufacturing specs, and tend to become a lot inefficient if forced to under such abnormal conditions.

For example a motor specified for operating with 60Hz may not be recommended to work with frequencies of 50 Hz or other ranges.

Doing so can produce undesirable results such as heating up of the motor, lower or higher than the required speeds and abnormally high consumption making things very inefficient and lower life degradation of the connected device.

However operating motors under different input frequency conditions often becomes a compulsion and under such situations a VFD or a variable frequency Drive circuit can become very handy.

A VFD is basically as the name suggests s device which can be used for operating an inductive load with the any desired frequency which might be most suitable for it as per its company specs.

This is normally done using the given control in the form of a variable knob scaled with different frequency calibration.

Making a VFD at home may sound to be a difficult proposition, however a look at  the design suggested below shows that after all it's not so difficult to build this very useful device (designed by me).

Circuit Operation

The circuit can be fundamentally divided into two stages: The half brige driver stage and the PWM logic generator stage.

The half bridge driver stage uses the half bridge driver IC IR2110 which single handedly takes care of the high voltage motor drive stage incorporating two high side and low side mosfets respectively.

The driver IC thus forms the heart of the circuit yet require just a few components for implementing this crucial function.

The above IC however would need a high logic and a low logic in frequencies for driving the connected load at the desired specific frequency.

These hi and lo input logic signals become the operating data for the driver IC and must include signals for determine the specified frequency as well as PWMs in phase with the mains AC.

The above info are created by another stage comprising a couple of 555 ICs and a decade counter. IC 4017.

The two 555 ICs are responsible for generating the modified sine wave PWMs corresponding to the full wave AC sample derived from a stepped down bridge rectifier output.

The IC4017 functions as a totem pole output logic generator whose alternating frequency rate becomes the MAIN frequency determine  parameter of the circuit.

This determining frequency is plucked from pin#3 of IC1which also feeds the IC2 triggering pin out and for creating the modified PWMs at pin#3 of IC2.

The modified sine wave PWMs are scanned at the outputs of the 4017 IC before feeding the IR2110 in order to superimpose exact "print" of the modified PWMs at the output of the half bridge driver and ultimately for the motor which is being operated.

Cx and the 180k pot values should be appropriately selected or adjusted in order to provide the correct specified frequency for the motor.

The high voltage at the drain of the high side mosfet must also be calculated appropriately and derived by rectifying the available mains voltage AC after suitably stepping it up or stepping it down as per the motor specs.

The above settings will determine the correct volts per Hertz (V/Hz) for the particular motor.

The supply voltage for both the stages can be made into a common line, same for the ground connection.

TR1 is a stepped down 0-12V/100mA transformer which provides the circuits with the required operating supply voltages.


The Half-Bridge Driver Circuit

half bridge motor driver circuit


The PWM Controller Circuit

Correction in the above Finalized Design

A careful investigation reveals that the diode feeds from IC2 in the above diagram is wrongly connected with the LIN/HIN inputs of the mosfet driver IC.

For a correct implementation of the VFD operation and the intended controls, the diodes must be integrated with the gates of the respective MOSFETs as indicated in the following corrected version:

The finalized integrated design of the above circuits may be witnessed in the following diagram, as drawn by Mr. Vuleek Unteeluv


R1 is for frequency adjustment, and R8 for Voltage Adjustment, both of these controls could be used for optimizing the V/Hz ratio for a particular motor, manually.

Note: Pin#16 of IC is shown configured with a PNP transistor stage which ensures that the IC 4017 keeps the mosfets powered only as long as its pin#14 is supplied with the cock pulses. This arrangement makes sure that under no circumstance the output of IC 4017 hangs and keeps one of the mosfets permanently ON and the other OFF, however if you feel the PNP stage is not crucial you may remove it and connect pin#16 directly with the supply positive.


Important: Make sure to connect the SD pin of the half-bridge driver IC with the negative or the ground line, otherwise the IC will not work.


Simplified and Improved Design

The above discussed simple single VFD design can be further simplified and improved by using a self oscillatory full bridge IC IRS2453, as shown below:

single phase VFD circuit using full bridge driver

Here the IC 4017 is completely eliminated since the ful bridge driver is equipped with its own oscillator stage, and therefore no external triggering is required for this IC.

Being a full bridge design the output control to the motor has a full range of zero to maximum speed adjustment.

The pot at pin#5 of IC 2 can be used for controlling the speed and the torque of the motor through PWM method.

For V/Hz speed control the Rt/Ct associated with the IRS2453 and R1 associated with IC1 can be respectively tweaked (manually) for getting appropriate results.


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

222 thoughts on “Single Phase Variable Frequency Drive VFD Circuit”

  1. Howdy, Friend! Interested to Learn Circuit Designing? Let's Start Discussing below!
  2. Hi Mr Swag i redesigned my H bridge driver and if i test it with motor ,my ic driver just brew up and the only pin that may course this problem is pin 5 since it connected to high voltage and there is no diode or resistor across it ,is it correct like this? im scared to put another one if it blow again i will be in short of them

  3. Thanks sir for your response.but if i connect pin 3 of ic1 automatically to ct of IRS what will be the benfit of ic2 ?? and i could not find IRS2453 in my city are there other replacements ?? and what about the previous circuit which uses IR2110 is it synchronized with the SPWM from the IC 555 or has the same issue ?

    • Hi Mohammad, IC2 is for generating the SPWM, IC1 is for generating sample triangle waves for IC2, all are interdependent with each other.
      You can Google “full bridge driver IC”, or half bridge driver IC, and see which one is available in your area.

  4. hi sir,
    if i have AC 220 V 1/4 hp compressor of household refrigerator and i want control its speed what is configuration suitable for Rt/Ct associated with the IRS2453 and R1 associated with IC1 ??

    • Hi Muhammad, the full bridge stage is actually not synchronized with the SPWM from the IC 555, therefore the output may not be correctly optimized AC. Therefore I would suggest to eliminate Rt/Ct, and feed the Ct pin of the IC with frequency from pin#3 of IC1.

      IC1 frequency may be set at the desired output frequency by measuring the output of IRS IC with a frequency meter and simultaneously setting the R1 220K preset…this will allow the full bridge stage to be synchronized with the SPWM control frequency and also allow to get the required 50Hz frequency at the output

  5. Thanks bro,one more question ,why is it necessary for Drain pin in HO side is connected to power while the other one is connected to load. will this not affect the mosfet ?,just asking i did read about the mosfet from the page you shared yesterday.

      • Thank you very much Swag we appreciate your help bro.i have learnt a lot now and i’m hoping to get this done before the second of may which is two weeks from now and i will be presenting my project but i’m still working on it.

  6. Hey swag .
    Plzz give me a motor rating …??my project is 1 phase vfd for 0.5hp induction motor can I used your circuit in my project ..??? Plzz help me broo

    • Hi Satyajeet, the motor rating will depend on the mosfet rating and the applied voltage to the drains of the mosfets, or vice versa, meaning the mosfet and the supply voltage could be selected as per the motor specifications.

  7. Hi Mr. swagatam.

    can u help me with single phase VFD run with arduino . MATLAB/SIMULINK code has been done to drive the bipolar full bridge PWM signal to MOSFET with variable frequency and modulation and will upload to the arduino.

    So, my problem is how to make circuit for gate drive the MOSFET to drive the 240V 70W ceiling fan.? can u give me any suggestion. Thanks..

    • Hi ISZ, An exactly similar question was asked many days ago by one of the readers and I had provided him and appropriate diagram for implementing the same, now it may be very difficult for me to search that particular comment.

      Anyway if you are trying to feed the bipolar pulses into a n-channel based full bridge mosfet configuration then you might require a bootstrapping mechanism for the high side mosfets, right? Without this you won’t be able to drive the high side mosfets, so have you taken care of this??

  8. hello sir ,i made a simulation for this circuit in multisim program but it doesn’t work for me.i can send you a photo from the simulated circuit if you wish sir :).

    • Hello Mohammad, Simulators can produce wrong and misleading results, how can you confirm it is giving you the right results? If you build this circuit step wise with proper understanding the circuit will surely work…

  9. Hello Mr. Swagatam, could you explain why the output (pin3) of the second 555 is connected to the HO and HI outputs with inversely polarized diodes? regards

    • Hello Mr. Benjamin, that is not correct, and I have mentioned about this and have presented the finalized design at the end of the post….the diode links must be connected with the mosfet gates.

  10. Hello Mr. Swagatam, would you be so kind as to send me the image of the last scheme that has the corrections to my email? Since when downloading the image you can not see the values of the components well. Greetings Benjamin

  11. Hello again .
    With all due respect brother I have one more question .
    1. Why 2nd 555’s I mean ic2 output is directly going to mosfet’s gate ?
    Please clearify this what’s purpose of it . If we remove ic2 from circuit it’s still working .

    • Hi, If you are not including R8 pot and not integrating the IC2 output with the mosfet gates, then you won’t be able to control the speed of the motor, the option will be simply lost.

      IC2 helps to transform or chop the mosfet gate drive into an SPWM format, and R8 allows the PWM control of this SPWM, meaning by rotating R8 you can reduce or increase the SPWM duty cycle or the width of the pulses. narrow width will cause decrease in motor speed, wider pulses will allow higher speeds.

  12. hello sir,
    we have completed this project and i have a few questions please answer these questions it will be a great help 1.why we are using 2 555 ic’s ?
    2. why we using pin 2 and 7 of 4017 ?
    3. we have used ct also for protection i will share the pictures .

    • Hello Farhan,

      The two IC 555 are used for creating SPWMs in response to the 100Hz sinewave ripple sample achieved from the bridge at pin#5 of IC2

      The actual sequencing of IC 4017 is from pin#3 > 2 > 4 > 7…by skipping pin#3 and pin#4, we are trying to insert a good “dead time” for the mosfets, although this can also result in significant amount of voltage drop at the output.

      Also, the use of a half bridge at the output could result in further drop in voltage.

      so the above things must be considered….

      the half-bridge could be replaced with a full-bridge driver circuit for ensuring the correct level of output for the motor.

      sure, the images will be greatly welcomed here,,,keep up the good work.

  13. We have hooked up the vfd in stages and began testing with and oscilloscope. We are getting a square wave coming out of pin three of ic2 and 1c1. We also looked through the previous comments and removed the 557 and other components as you stated. What should we be looking for on the oscilloscope going to the 4017 and further more on the ir2110?

    • isolate the IC1/IC2 entirely and test it separately, connect the upper arm of the R8 pot at pin#5 of IC2 with the positive line.
      varying this pot should create a variable PWM at pin#3 of IC2. The frequency of this PWM can be varied by adjusting R1.
      Once this is confirmed, connect the R8 upper arm with 100Hz from the bridge, and check whether pin#3 of the IC 2 is producing an SPWM or not, it should.
      Once this is confirmed you can integrate the IC4017 with this stage and verify the alternating pulses across pin#2 and pin#7.

      similarly confirm the motor half bridge driver separately and finally integrate it with the IC 4017 output

  14. I have hooked up the whole circuit and i am able to vary my current. The problem is i am feeding the top mosfet with 170 v dc to run a 120vac motor but I’m only seeing about 4vac across where the motor would go. Any thoughts on the possible issue?

    • Hooking up the whole circuit is not the right way to go, you must build it stages-wise and confirm the stages separately, once confirmed then you can integrate them together for the finals results….as you can see there are many stages in the design, unless you are sure each one of them are doing their job correctly you cannot be sure of the output performance.

      please check the mosfet gates with an oscilloscope, check what waveform you get here? If it’s an SPWM then it is fine otherwise you may have to go right back and begin investigating from the IC1, Ic2 stages.

  15. Thanks for answering Mr. Swagatam. Excuse me I thought the circuit was for that purpose (vary the speed). But could I use it for that purpose or not?

  16. Hello Mr. Swagatam, first I wanted to thank you for all your contributions to fans like me.
    I have a doubt about the circuit, by reducing the frequency of the motor this consumes more current, how do you solve that problem. As far as I know, the voltage applied to the motor must be reduced, but I do not see that system in the circuit. Greetings Ben.

    • Thank you Benjamin,

      The frequency adjustment here is not for controlling speed, it is for ensuring that the motor operates with the correct frequency as specified by its manufacturer. It is specifically used when a 60Hz motor is being used with a 50 Hz source and vice versa, and then the pot may be used for correcting the frequency as per the spces.
      the voltage output can be varied by adjusting the pot at pin#5 of IC2

  17. Good morning sir. Pls, after putting up the circuit, I realised that there was no signal entering into pot 14 of IC4017. Sir, pls, wat do u think could be the problem? Thanks in anticipation as I await your response.

    • Good morning stephen,

      if you put up the whole circuit together, it is never going to work for sure, and that’s true for most of the circuits which have different stages.

      you should build and confirm them stagewise, and this will require some serious understanding regarding the various stages.

      anyway, by pot 14 you mean to say pin#14?

      from where is pin#14 getting its signal? it is from pin#3 of IC1 right?, so check whether your IC1 is oscillating or not…keep verifying all the stages in the same manner.

      by the way the following parts can be removed from the last diagram

      T2, R9, R10, C7, C6, and connect pin#16 of IC 4017 directly to the positive line

      • I have done what u told me to do but what I realized is that it is only the pin Ho dat has voltage on it while the pin Lo does not and variation of the two potentiometer does not have effect on the Ho and Lo voltage. Sir, what else do u think I can do.

        • did you check whether IC1 was generating the oscillations or not…. in response to these osculations at pin#14 of the IC4017 it is supposed to generate alternating ON/OFF voltage across its pin2 and pin#7, isolate the respective stages and first confirm them separately….checking HIN and LIN can be done later on…

          IC2 pin#3 should be generating varying PWM in response to a varying voltage at its pin#5, this is the next possible thing that you must confirm

  18. when the R8 potentiometer is adjusted, what is the variable parameter here? its variable the voltage or variable the ripple frequency 100Hz to pin 5?

  19. Good day sir. Pls, I don’t know if you can help me with a mathematical analysis of how you arrived at the values of each of those components used in the circuit. Thanks in anticipation.

  20. Will a 1HP, 230V motor work with this circuit? Please reply ASAP cuz i am making this as my project and need to submit it within a couple of days. Thank you.

    • motor power rating can be matched by suitably upgrading the mofet rating, so any desired motor rating can be used…

      however make sure you have understood the circuit and stages perfectly before you try it.

      the circuit will need to be built stage-wise, by confirming and testing each one step-wise, and then integrate them for the final outcome

      • If we supply it with 330V DC, won’t it affect the circuit? Cuz the voltage will get supplied to other parts of the circuit too right?

        • We are getting a DC output across where we are supposed to connect the motor for output….around 200mV, we haven’t given any motor voltage yet….So basically without motor voltage and motor….we are getting a 200mV DC output…is it working that means? And also….we are using a bred board so how are we supposed to make the ground connection to 0?

          • sorry, that’s not the right way to check…you must verify the various stages separately.
            using an oscilloscope first confirm whether the IC 555 stage is delivering the PWMs or not ( by varying the respective presets)
            then verify whether the IC 4017 is responding accordingly or not, and then finally verify the output from the half-bridge and check if it is producing the PWM based chopped square cycles across its output pins…all these will need to be done via an oscilloscope.

            • ground connection refers to the negative line from the power supply, all the negative lines must be connected in common, including the motor supply’s negative line.

    • Daniel, yes that may be possible, however R8 is also synchronized with the mains cycles, so your Arduino will also need to be configured to do this…

  21. If I didn’t use 240v/12v transformer (but use direct supply with 12V adapter), how I can variable for voltage adjustment at potentiometer R8 ?

  22. hi dear swagatam
    I have a question about drive half bridge circuit IR2110
    in half bridge source pin upper conected to drain pin The bottom ؟

    Thank you

  23. hi sir, good day.

    Im not familiar with the 555 timer ic and 4017 ic. can you explain more details about how its works for both type of ic in this circuit. can we control LN & HN at IR2110 ic with microcontroller ?

  24. hi,
    can i change the K2837 mosfet with another type? from your opinion, what type/brand of other mosfet that can be use because i cant find this type of mosfet in my county.


    • Hi, the voltage and current rating of the mosfet should be a little higher than the load’s V/I rating, as long as this is satisfied any equivalent type of mosfet can be used. you can confirm it through the datasheet of the selected device

  25. Hi Mr. Swagatam,

    I wonder how do we know if we have the correct v/f ratio since it doesn’t automatically change the frequency or voltage when we turn the potentiometer. And what will happen if we don’t get the correct ratio.

    If i put resistor parallel to R1 and R8 is it possible to make it auto adjusment for v/f? I mean i put fixed resistor for R1 and R8 in a v/f ratio and put another potentiometer in parallel to those so i only need to adjust 1 potentiometer to get the speed.

    • Hi Ari, The correct V/F ratio can be obtained from the motor specifications, and in the circuit these two parameters can be fine tuned using the R1 and R8 pots.

      auto adjustment is actually not required because the supply from the grid will be relatively constant and will not disturb the settings.

      if you don;t get the correct ratio your motor will not be able to run at the optimal range, however accuracy is not critical here…

      • Hi Mr. Swagatam.

        Thanks for you reply.

        I mean how do we tune the R1 and R8. If we turn R1 to get a speed then i should adjust the R8 too to get correct V/F ratio. How do we know we adjust it to correct ratio. My motor is 220V 50hz, it means ratio is 4.4. So do we just measure the resistor R1 then adjust R8 accordingly to ratio?
        Thank you.

        • Hi Ari, R1 can be used for adjusting the frequency, for example say from 50Hz to 60Hz etc.

          R8 can be used for changing the voltage level, R8 will basically change the PWM which will in turn help to change the output voltage. changing R1 will impact the waveform slightly as it will alter the number of “pillars” on each output wave when viewed in the PWM mode, but this will not affect the load

  26. dear brother i want to ask how we are varying voltage and one more thing. is mosfet acting as an inverter ?

  27. hey!
    I have got a problem. Circuit is not working for me. I am using single phase AC motor 0.35A 230V. I also measured signal on load – nothing else except around 12V peak to peak distortion. I used the same parts as you. For motor supply I used rectified mains voltage: 310 V DC. Also with oscilloscope I noticed, that PWM signal going out of 4017 and also driver is okay.

    • It seems your driver IC has problems and is not responding to the processed signals from the IC 4017, please check whether the 4017 output is feeding the signals to the driver IC LIN/HIN inputs or not, and check whether the driver IC output is feeding the signals to the mosfet gates….you can confirm these by temporarily disconnecting the PWM diodes across the gates of the fets.

      initially use a 220V filament bulb for testing the response

  28. Hi swagtan . well i really like your articles on this tech stuff. well i did make the circuit and i have no oscilloscope or fancy lab test equipment but then i managed to hook a incandescent bulb to test it first. There was a bit of success on the dimming effect or something like blinking cause of the lower frq. but then.. i actually used a mosfet that is 500v and 20A but and all i did is to do away with the ir2110 and i drove the mosfet directly. The bad news is that when i hooked a 750watt induction motor to test, there was the magic smoke from the first 555 timer and then i also noticed that the mosfet to was gone… damn i couldnt tell wat exactly went wrong since from my math the 20 A FET was good to handle the motor!

    • Hi Paul, Thanks for updating your experience with the design, although I am not exactly sure of the problem you faced, nevertheless the last design certainly needs a correction, I'll update a few improved designs soon in the above article which according to me will make more sense technically. kindly bear with me.

  29. Thanks for your quick reply.

    As I know, when intensity of sunlight increases, the voltage output from the solar panel will also be high, to maintain speed of the motor, VFD will adjust Voltage/Frequency ratio. And these job will be done by VFD automatically. (Correct me if I am wrong)

    But, from your circuit diagram, it looks like, there no option to change the frequency. It is fixed to a single value by placing a capacitor.

    • Thanks a lot

      That means i have to cascade these 2 circuits i.e. the 1st one is above circuit and at the pin no.5 of IC2 of above circuit, i have to connect the 2nd (simple solar MPPT circuit).

      Or something else?

      Thanks & Regards,

      Nitin A Kallole

  30. First of all Thank U Very Much Sir…

    I have some doubts regarding above circuit.

    1. Can we use same circuit for solar powered pumps. In solar powered pumps/motors that draws water from bore well, the job of VFD is to control speed & torque of the motor.
    2. If yes, does it use MPPT (maximum power point tracking) algorithm.
    3. As intensity of sunlight is not same throughout a day, the job of mppt draw maximum power. So that, these VFD's will work in cloudy climate also.

    Thanks & Regards,
    Nitin a Kallole

    • Thanks Nitin,

      yes you can use it for varying the speed of the motor.
      A VFD is not related to MPPT according to me, so MPPT is not relevant with this device.

      Said that, you can surely employ an MPPT externally for ensuring maximum efficiency from the solar panel.

  31. respected sir,

    i have single phase induction motor which has spec. 1hp,7 amp.,50-60hz frequency, 1440 r.p.m

    this motor i used in power press machine now i required to control the speed of motor, i had been used dimmer switch which was rated 3000watt but motor run on full load dimmer was failed so now i required to control motor speed from frequency control method so which kind of replacement is need in this circuit. when motor run on full load that time amp goes to 8 to 10.5 so which component is need to control this high amp. also i can not effort readymade vfd drive.

    hope you will help me as possible as soon

    kishan s ghetia

    • Hi Kishen,

      A VFD may not be suitable for your application, you will need either a dimmer which you have already tried, may be due to low power triac your dimmer got burnt, I think you can try a dimmer with a 40 amp triac such as a BTA41/600, and mount it over a big heatsink.

      you can also try a PWM version for the same.

      I have explained the circuits in the following article which you can probably try.

      But these are relatively complex circuit and only experts are advised to work with the.


  32. dear, sir
    i have SINGLE PHASE INDUCTION MOTOR 1HP, 7AMP, 50-60Hz frequency , and r.p.m is 1440 which is use in power press machine .
    now i want to control speed of motor by using this circuit so which kind of modification will required. when motor run on full load it's amp was 7-10 so what kind of component is replaced in this circuit. please give me the list of component

    in past i had been used dimmer switch which is rated 3000watt but it had been failed in full load of motor so i want to control by frequency method.

  33. Hello sir, my team has purchased all the components for this project. We have also assembled the circuit on breadboard. Now, we have some doubts. Please help us out with them.

    1. In the diagram drawn by Mr. Vuleek Unteeluv, it is said that we have to connect "motor voltage" at the drain pin of "HO MOSFET". I assume it to be the single phase voltage. If I connect the phase wire at the drain pin of "HO MOSFET" then where should I connect the neutral terminal? Should I connect it at the source pin of "LO MOSFET"? If I do so, I fear that the negative of DC voltage (Ground symbol of diagram) and neutral of AC will get shorted.

    2. Is it compulsory to give rectified 12VAC or can I connect 12V battery.

    Please help sir. It's urgent. Thank you very much for your support.

    • Hello Akbar,

      NOT the phase, you'll first need to rectify the mains 220V AC into DC (330V)using a bridge rectifier, and then connect the positive with the mosfet drain, and the negative with the source….

      the 12V can be any form of DC…the word "rectified" refers to the conversion of a 12V AC to DC that's all nothing critical about it.

      • Thank you so much sir for your quick reply. I understood the circuit now. Just for verification I am mentioning what we will do:

        We will connect 12V battery for 12V DC power

        We will rectify AC (by using our own external bridge rectifier) to 330V DC and then give positive to MOSFET (HO OUT) Drain and negative to MOSFET (LO OUT) source.

        So this basically means we need to design our own simple 330V rectifier. After reading other comments I believe that this rectified voltage must not be pure DC but should have some ripples in it to act as sampling.

        Am I correct Sir?

        Also, second doubt I have is:
        Ground of 330V DC and 12V DC will then be same if I connect negative of 330V DC to source of LO OUT MOSFET. Will it be safe? I mean, it will not cause any circulating current?

        Thank you again for your quick reply to my previous doubts. Do reply soon.

        • You are welcome Abrar!
          the 310V DC can be a pure DC, it need not be with ripples, although ripples might not affect the motor performance.

          but pin#5 of IC2 will need a 100Hz sampling…so I think the last diagram has a mistake, it's not as per the second diagram (pin#5 needs to be connected to 100Hz ripple separately)….I'll correct it soon

          yes the negatives of the two voltages (310V and 12V) should be connected in common, there's no danger in doing so and is necessary to make the circuit work correctly

          • Thank you again sir for quick reply.

            1. Sir how would I provide 100Hz sampling to pin 5. Is there a separate circuit? If yes, then which circuit?
            2. Can you please recommend us a 230VAC to 330VDC rectifier circuit?

            Sir do reply soon because we have to build the pcb footprint by tomorrow night.

            I know, I don't need to mention again and again to reply soon because you are very fast in helping. Its just that we are in urgency. Sorry for disturbing you.

            • Thank you Abrara,

              A rectifier can be built by using 4 diodes as shown in the diagrams above….I have corrected the last diagram you can check it out

              But I wonder if you don't know how to build a rectifier how you would be able to succeed with the above fairly complex circuit?

  34. i did work little bit on VFD ,but my requirement is to run Air Conditioner Compressor motor of 1 ton . i tested above circuit ,it showed Pure Sine Wave at the output but this Sin wave remains stable just on 50 HZ frequency , on slight variation in potentiometer value ,it shows various noises .My aim is to vary frequency in between 20 to 50 hz with sin wave. The above circuit is feasible for 1 hp and i need to upgrade it to 4.7 hp ,3.5kv and 15 amp let me know sir how could i do that .

  35. I did work little bit on VFD ,but my requirement is to run Air Conditioner Compressor motor of 1 ton . i tested above circuit ,it showed Pure Sine Wave at the output but this Sin wave remains stable just on 50 HZ frequency , on slight variation in potentiometer value ,it shows various noises .My aim is to vary frequency in between 20 to 50 hz with sin wave. The above circuit is feasible for 1 hp and i need to upgrade it to 4.7 hp ,3.5kv and 15 amp let me know sir how could i do that .

    • You can upgrade the power of the circuit by connecting more number of mosfets in parallel.

      50Hz is for 220V…and 60Hz for 120V and so on…so the frequency should be in terms with the voltage level as per the standard specs…..and by the way noise can be filtered by suitable LC filter circuits

  36. I see the question of 'have you built this circuit and tested' was a no. Has "anyone", successfully, made this work? I just finished drawing it in eagle cad. When my dad asked – is this a tried design or just another Internet postling. So, I have to know is there a working board out there?

  37. Im using 200 volt supply, and need frequency range from 0-50 Hz or around it. It can be less than 50Hz but i need low frequency. Which circuit will help me from these three? If not then can you provide me one?

  38. I really need to use AC main to power my DC motor instead of battery. I have 19amps 27v 2200rpm permanent magnet DC motor which consumes 36v 200ah battery anytime I want to test run it. Help me design an AC input/DC output that will handle 19a 27v DC motor without voltage drop.

    • The best and the safest way would be to use a 24V 25amp transformer, and rectify its output for the motor…this could be made by anybody safely and with 100% results…any other option could be risky and might require advanced knowledge regarding the concept.

  39. actually brother My requirement is to run single phase 2hp 220v 50hz 12amp motor using solar power, i am having 800v dc 4800watts solar panel int that i want to use mentioed single phase motor and also want home purpose, can i use this circuit as for my req.? What model mosfet iwant to use?

    • yes brother definitely you can use the circuit, make sure to select the mosfet as per the load specs.

      however you must have the assistance of an expert electronic engineer while building the proposed circuit because the circuit could be too complex and not suitable for the newcomers.

    • Got it brother, the borewell submercible pumb having three wire system 240v single phase, in that case how the circuit is used to run the motor ?

    • I think one of the wires out of the three could be for "earthing" purpose…while the other two for LIVE and NEUTRAL connections…you will need to find the Live, and the neutral wires and connect these between the mosfets, as shown in the diagram.

  40. Hello 🙂 i'm back.. 1 month has passed since i posted. Couldn't work on the project because school started,had some exams at another course,and i had driving license exam..soo i didn't had much time to spend on the project. I worked on my PCB these days,and there are good news and bad news. The bad news are that i missed something,and some components heated up. I solved the problem but my circuit has no output. I tried to ask some help ,found that i had my IC3 output was messed up and tried to fix the problem ,but then i found other things and so on… My worst nightmares. Tried to solve everything,and in this point my PCB has many jumpers and looks horrible but i have an output,with the Hz meter i read from (if i remember) 10 to 1100 Hz aprox. but if i connect a load it doesn't do notting. Forgot to mention,i rectified 220v ac with rectifier and caps. and i supplied the circuit with 310vDC to see if i have an output,and my AC output voltage varies from 0,9V to 2V but it's somehow instable(sometimes shakes from 1.8v to 2.1 by itself) And unfortunately,i dont have an osciloscope so i can't test if my 555's work fine,or if i have a stable 1kHz output. But the good news are that i won't stop untill i make this circuit work. And i have a good ammount of spare parts,so no problem. I learned something about the IC's from the datasheet's and i understand a little bit more how the circuit works. I focused on your 2 first images,the one with the 555's and the one with the mosfet driver,checked the datasheets,found some errors with my pcb desing,and in these days when i have some free time,i will change the PCB design ,make a circuit diagram and correct the errors,hope this time it will work. I'll update the DropBox link content as soon as i correct all the errors,but i really can't be sure if i will not miss something again,because i allways miss something…for now. Anyways, if you have some time to answer some questions please. For IC2 555 at pin 5 ,like in the second image, we can use the positive 100hz dc ripple(if i say it right) , and you suggested that we can use instead a 1KOhm potentiometer like in the final circuit diagram from Mr. Vuleek. But how a potentiometer can transform a 12v DC powersupply into 100hz ripple for the pin5 ? Have you tested the circuit if it works? Some good advices? Hope i didn't missed some word,because it's late and i'm a little tired. Really wish i could understand this circuits concept from the core,because as you warned,it is frustrating sometimes but it doesn't matter,eventually it will work. Thank's again 🙂

    • I appreciate your interest and determination and wish you all the best!

      This circuit can be difficult even for an reasonably expert engineer like me, so it can be definitely a huge thing for a school student, so whatever you could achieve so far is commendable.

      Anyway, the right method to build a complex circuit is to go about stage-wise…..never try building the whole thing at a one go….in that way even an expert engineer might end up with flaws and fumes.

      My advise would be to first disconnect all the interconnecting loops….

      disconnect the IC 555 from the IC 4017…and IC 4017 from the motor bridge driver

      power the IC555 section separately and make sure the 4017 and the motor driver do not get any power DC

      After this, check the output of the IC2 pin3 by adjusting the 1K preset….1K preset changes the potential level on pin5 which is compared by the triangle waves at pin7 of the same IC internally for generating a proportionately varying PWM at pin3.

      As pin5 potential drops…the PWMs at pin3 get narrower and vice versa.

      You can check the following post for the details


      check and confirm the pwms using a scope or simple a DC voltmeter at pin3.

      once this is confirmed, you may connect the stage with the 4017 IC and check its output whether or not it generates the required sequencing output across its selected output pinouts.

      And finally you may integrate the 4017 output with the motor driver IC for verifying the final results.

      I hope you understood how it needs to be implemented…if you have more doubts feel free to express them here….

  41. I'm back, finished at last the PCB in sprint layout and i uploaded everything to DropBox https://app.box.com/s/yzlqg67ei0y8o6nulic19aj56in3leu3 with the updated schematic, .LAY file and everything that i found to be useful for me. I double-checked the PCB to be sure and in 2-4 days will arrive to me,so i can start soldering. Hope i didn't missed something, i have nightmares when random components start to heat with no reason… i'll make an update when i finish and test the PCB 🙂

  42. Waw… 600V DC input,that is something… It will be hard to reach such volts. If i recify a 220V AC supply with filter capacitors it will reach 310V DC,is that enough to power my 1A 220v AC single phase motor? i know we have a potentiometer for V and Hz but how it works? if i have 310V DC supply i can change the output voltage from 0 to 310V AC to power the motor? And on top of that i have problems with the parts list, i have to buy equivalents for the IC's. I have CD4017BM SMD for the decade counter/divider, IR2110PBF for mosfet driver and SA555N for astable/monostable timer. I can buy only from TME. Thinking they are fine withs specifications,what do you think? Ooh,and thanks for the reply 🙂

    • 600V won't be required if you intend to control a 220V motor…yes 310V would be just right for your application, and you would be able to adjust the RMS right from 0 to 310V

      The numbers of the parts you have mentioned are all OK according to me, and should work as specified.

    • Let's say i'm not an hardcore expert,but for my level,this project looks fine to do,still it's a demanding one…My weakest point is to understand how the circuit works,how the IC's works and how to combine them to make a magic output ;P. Got all those fancy terminologies in the description that drive me crazy, but i have years to learn. For now i just follow the diagrams,make the pcb's,solder everything and make them work,one day i will learn the theory behind the hardcore circuits that i encountered. Just got the information that my K2837's can't arrive,so i'll use FDA50N50 for the power MOSFET's,they have low Rds=89mO, Vds=500V, Vgs=+-20v and Id=48A,they must also be fine. As soon as i finish the PCB in Sprint Layout i will post some images for the others too see it,an image with the updated schematic from Mr. Vuleek Unteeluv with the 310v DC input correction and upload the .LAY file of PCB for the others to use it. Thanks :).

    • There are too many things to be learned and digested in the shown design, one explanation could need a subsequent explanation to be understood and the strings of such explanations can be quite long.

      however If you are confident then you must go ahead.

      The mosfets are not so critical, it just needs to be matched with the load specs for preventing it from heating up too much.

      certainly, would love to see the images:)

      wish you the best!

  43. Hello Swagatam, nice project you have here. I just started to make the components list and pcb to order so i can build your VFD,it's perfect for my 250W ac single phase motor. Thank you for sharing the project :). I have some questions if you dont mind. In the first picture we have an IC IR2110 and the drain side of the mosfet goes to an electrolytic 10uf/1KV capacitor and to: Up to 500v or 600v, but in the third picture the drain side of the mosfet goes only to the electrolytic capacitor . so the question is how the ac single phase motor powered? and where we have ac or dc because its a little confusing,the up to 500v or 600v is ac or dc ?. Many thanks!

    • thanks mtn, in the last diagram the drain of the high mosfet needs to be connected to the desired high voltage DC bus source,,,yes it's not shown in the diagram, if possible I'll tru to update it accordingly soon.

      please note that the design is a manual VFD so the V and Hz will need to adjusted manually through the indicated pots.

  44. Hi Sir.., my project is upon Single phase Induction motor of 60W,230V,0.28A rated…My query in this circuit is that at the Inverter output terminal is that possible to achieve 230V ac with 12V battery as input. or I supposed to put step-up transformer..

    • Hi Hemanth, if you apply 230V at the mosfet drain side then the output will be optimized for 230V, so basically the output will depend on what input is fed to the drain side of the upper fet.

  45. dear sir i am getting problem in half bridge driver circuit part in this circuit…control part is working well….can u make me understand hoe this part is working…

    • dear anshdeep, the input HIN and LIN should be connected to the 4017 outputs, thus when HIN is high, LIN should be low and vice versa, as long as this is happening the output of the IC will switch the mosfets and the connected load….the shut down pin is not relevant and may be kept open.
      alternatively you can simply eliminate the entire 4017 stage and the half bridge, and connect a mosfet directly with the pin3 of IC and drive the motor through it.

    • Anshdeep, I was wrong when I said the 4017 can be directly used for driving the motor…it cannot be used because it cannot replace a half bridge driver IC, that is why we have to employ the indicated IR2110 IC

    • Dear Ups, can you provide some more details about the application and the requirement, it will help me to design the circuit in a better way.

  46. Please specify the type of motor to be used. May I use a split phase capacitor start fan motor? And also specify the frequency range of first IC for satisfactory operation of this project. I am doing this circuit as a project for my students and have to design the transformer based on your reply.Please reply.

    • I have no idea which motors typically require an VFD, I have only tried to present a suitable circuit based on the studied concept

      the frequency range can be between 10 and 500 Hz if 1uF is selected for Cx

      • Hi sir im having a same problem with the circuit its not working ,and when i connected it to 230 AC V my high side mosfet just burned.and the following is my motor specification

        This unit will handle all high voltage (220VAC) and drive the motor.
         Drive 24W 230VAC induction motor.
         The speed of the motor should be determined by the Speed Reference unit.
        the motor to be drived is “Mellor Electric AC1000 Reversible Shaded Pole AC Motor, 24 W, 1 Phase, 2 Pole, 230 V ac”

        please help bro i connected the circuit as it is but i used IRF460 in the beginning also tried IRF540 as my mosfet both of them burned.

        • Hi Ayada, how did you build and check the stages? If you build the whole together it is never going to work.

          You must build the different stages separately, test and confirm them separately, and once all these stages are verified, then you should go for the final integration step by step.

          Here first you must check the the IC1/IC2 555 stage separately and make sure the PWM is working in sync with the bridge rectifier ripple input and also make sure PWMs are varying with the 1K pot, then test the full bridge driver separately with a motor, then finally integrate all of them to check the motor speed variations.

          • hi sir thanks for your patient but i did that and my PMW is working very perfect my output is very good i checked it using oscilloscope i will share the results when i get to LAB and i did my PMW stage in breadboard and the high side stage which compromise the two mosfets i built them in veroboard, and if i check it separately my mosfets just burnt that why im confirming from you sir and i first tried it using the 12v but i was unable to read the change in frequency using oscilloscope then i applied 230 v then the mosfet burnt 2 times i used IRF460 and IRF540 separately and the first once made a big noice and the second ones just burned and followed by smell so i dont know yet but im going to double check my veroboard again but tell me in which way i should build and test the The Half-Bridge Driver Circuit should i put them all in veroboard including IR2110? lastly sir what can cause the mosfet to burn in this design specifically?
            Thank you.

            • Thank you Ayanda, if the IC 555 PWM stage is working perfectly, that means the half bridge stage is giving problems. However the half bridge design is a standard design taken from the datasheet of the IC, so it has to work.

              Yes the mosfet placement is crucial. The IC and the mosfets must be assembled on a PCB by soldering and very close to each other.

              Also connect a 1K resistor across all the mosfet’s gate/source leads. For more info on this you can read the following article:


  47. this circuit is not working……can anyone help me to understand working of all major components in this circuit….plz

    • pin5 of IC2 should be connected to an AC source, for example a 100Hz ripple from the a bridge rectifier.

      This is for setting the amplitude of the PWMs in accordance with the mains AC value.

      However this can set using a 1K pot also.

      remove the pin5 (IC2) link entirely.

      take a 1K pot and connect its center pin to pin5 of IC2, the other two outer pins should be connected to positive and negative of the supply respectively.

    • Thank you Swagatam Majumdar for your help. I appreciate it.
      I hope now all is correct. i61.tinypic.com/2nkj6le.jpg
      What about resistor wattage and c11 capacitor? Am I right about them?

    • It looks perfect to me now.

      All resistors are 1/4 watt……C11 could be an electrolytic, or 10nos of 1uF/1KV (MKT)connected in parallel

      • Hi sir ,you once mentioned that c11 will avoid the voltage spikes accross the lines,and its seems imposible to get 10uf/1kv but i managed to get 103/2kV there is a problem if i use it or its must have a big value or smaller than?

        • Hi Ayanda, yes that’s right C1 is very important, but it should be at least 1uF in value, 103 will simply not work because that’s equal to 0.01uF, too small to cancel any spike effectively.

  48. I drew one single circuit (connected 2 circuits together) and I'd like you to confirm that all is correct in it, if possible.
    I cant post images in the comments.

    • you can send it to my email which is given in the "contact" page, or upload to any free image hosting site and provide the link here.

  49. Hello Swagatam…

    Have you tested this circuit? What kind of motor have you tested? With which motor voltage? Did have the motor capacitor? Did the motor heat to much? The control of spinning was quite linear…? Sorry for too many questions, but I intent to build it with Microcontroller in the control part, for a Fan… If it works , i could share with your website…

    • Hello Julio,

      I have not tested it yet, but everything looks correct to me in the design… you are welcome to share your design here, I'll publish it with your credentials

    • Julio, I also want to use it to control the fan motor. I'm more interested in controler (AVR) use. Could be used and the temperature feedback to prevent damage to the motor. For this case, use only the power control scheme. There remains a number of issues:
      – What should be the PWM frequency? Low frequency noise is larger, poorer control, excessive frequency may cause heating of the parts, as well as might not be able to close the transistors and the scheme shall be burned.
      – Galvanic isolation and would preferably otherwise remains electrical injury.

    • PWM frequency can be such that chops each square wave into 4 blocks, multiply the basic frequency with 4 or 5, that will give you the PWM frequency.

  50. Hi,
    how to use the Arduino (as a PWM generator). It must also be insulated phase (eg. Optocouplers). What do you think? How to realize this?
    With respect Evaldas

  51. No i want to use the AC motor for my project, thats why i was looking for a self-built VFD, but without variable Cx it not be suitable for my project. And do you want to have the rectified AC from the transformator on pin5 at ic555 no.2 or could it be dc aswell?

    • VFD stands for variable frequency drive, meaning the frequency should be variable as per the motor requirement, you could make Cx fixed and use R1 as a variable resistor for the same, if the frequency is not variable the purpose of the circuit would become meaningless.

      the input is taken from a 100Hz bridge source to make the AC mains input cycles synchronized with the circuits PWM output cycles.

  52. Hey, i have a few questions, is the resistor next to the ic4017 a 1kOhm too, and which ranges should Cx be, and also is it possible to run this setup with dc input only, cause i would like to power a RC-car running with an asynchronous single phase motor.

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