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3-Phase Signal Generator Circuit using Opamp

3-Phase Signal Generator Circuit using Opamp

Many a times we find it crucial and handy to possess a true three phase signal for evaluating many different electronic configurations such three phase inverters, three phase motors, converters etc.

Since it's not so easy to incorporate single phase to three phase conversion quickly we find this particular implementation difficult to acquire and enforce. The proposed circuit enables the above discussed well calculated spaced and positioned sine waves outputs to be generated from a single master input source.



Circuit Operation

The circuit functioning of the three phase waveform generator circuit may be understood with the help of the following explanation:

An input sine sample waveform is fed across the point "input" and ground of the circuit.This input signal gets inverted and buffered by the unity gain opamp A1. This inverted and buffered signal acquired at the output of A1 now becomes the new master signal for the forthcoming processing.

The above buffered master signal gets once again inverted and buffered by the next unity gain opamp A2 creating an output with zero degree initial phase across the points "Phase1"

Simultaneously, the master signal from A1 output is phase shifted by 60 degrees via the RC network R1, C1, and fed to the input of A4.

A4 is set up as a non-inverting opamp with a gain of 2 in order to make up for the signal-loss in the RC configuration.

On account of the fact that the master signal is phase shifted 180 degrees from the input signal, and further shifted to an additional 60 degrees by the RC network, the ultimate output waveform gets shifted by 240 degrees, and constitutes the "Phase3" signal.

Now, the next unity gain amp A3 sums up the A1 output (0 degrees) with A4 output (240 degrees), creating a 300 degree phase shifted signal at its pin#9, which is in turn inverted appropriately, shifting the phase to an extra 180 degrees, creating the intended 120 degree phase signal across its output indicated as "Phase2".

The circuit is intentionally wired up to work with a fixed frequency in order to yield better accuracy.

Fixed values are used for R1 and C1  for rendering the intended, accurate 60 degree phase shifts.

For specific customized frequencies, you may use the following formula:

R1 = (√3 x 10^6) / (2π x F x C)

R1 = (1.732 x 10^6) / (6.28 x F x C1)

where:
R1 is in kohms
C1 is in uf

Circuit Diagram



Parts List

All R = 10 kohms
A1---A4 = LM324
Supply = +/- 12vdc

Frequency (hz)R1 (kohms)C1 (nf)
10002.7100
4006.8100
604.71000
505.61000

The above design was investigated by Mr. Abu-Hafss and appropriately corrected for obtaining legitimate responses from the circuit, the following images provide a detailed info regarding the same:

Feedback from Mr. Abu-Hafss:

I needed a 15VAC 3-phase supply to test 3-phase rectifiers. I simulated this circuit the other day but failed to get proper results. Today, I made it work.

IC A2 and resistors connected to pin 6 could be eliminated. The resistor between pin 7 and 9 could be connected between the main input and pin 9. Phase-1 output can be collected from the original AC input. Phase 2 and 3 can be collected as indicated in the circuit.

However, my actual requirement could not be fulfilled. When these 3 phases are connected to a 3-phase rectifier, the wave form of phase 2 and 3 gets disturbed. I tried with the original circuit, in that case all three phases gets disturbed

Finally got a solution! A 100nF capacitor connected in series with each phase and the rectifier solved the problem to a great extent.

Though the rectified output is not consistent but, it is quite acceptable

Update: The following image shows a much simpler alternative for generating 3 phase signals with accuracy and without complicated adjustments:

SHARING IS CARING!

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!



95 thoughts on “3-Phase Signal Generator Circuit using Opamp”



  1. Hi,

    We have connected the circuit as given in picture3 as done by Mr. Abu-Hafss.

    The output for 120degree is not coming , it is only 60degree phase shift. for obtaining 120 degree phase shift i had to connect one more RC circuit at the output of U3. please help with this.

    Please explain the working of the summer used.

    Also, what is the value (1.732*106) is the equation, R1 = (1.732 x 106) / (6.28 x F x C1)

    Thank you in Advance.
    Chaithra

    • Hi, This circuit was referred from another article long ago and not designed by me, therefore regarding the circuit functioning I won’t be able to suggest much.

      Regarding the formula, I have updated it in the article with more details. Most of the variables in it are constants.

  2. Hello. for the updated circuit, could you tell me what the resistance and capacitance is to make the 50 Hz frequency? And how to change the frequency with the resistance?

    • Hello, I assume that it is originally calculated for 50Hz, nonetheless you can practically test it and tweak the results if required by changing the R or C values accordingly…

  3. Hi Swagatam,

    Can the variable frequency signal [ from 1 to 60 Hz] circuit from timer 555 to feeds into its controlled board to run a salvage 3phase induction washer motor from 120VAC ?

    • Hi Cong, if you change the frequency in IC 555, it will also proportionately vary its PWM, it's better to use IC 4060 for getting a variable and perfect 50% duty cycle frequency…but the output will be a square wave which might not suit your induction motor

  4. Hello Mr. Majumdar, I would like to ask you how did you get the 60 degrees phase shift to sum up with the 240 degrees from A4? thanks for your time

    • Hello Rich This design is not mine, rather taken from another source, I have not yet investigated the calculations so far, so can't comment regrading it..

    • Oh ok, hehe. I have to check then. The thing is that I used this network for my work. Works fine and I understand all the process except that part I asked you.
      Thanks anyway for your time.

  5. Dear Majumdar,

    what is the input value of the ac in the above circuit..? and how much will be the out put ac?
    Actually i need 3 phase 24 or 12V ac at60Hz out put. and i have 12 and 24 v ac 60Hz.

    • Dear Basheer,
      the output will be equal to the peak to peak value of the IC supply voltage, if the supply is 12-0-12V then the output will be also in accordance with this value,

      The input could also be equal to this value but not above this to avoid voltage clipping.

  6. Hi Genius,
    I want a circuit that can convert single phase AC( 220v 15 amps 50-60 hz) to three phase 120 deg phase shift ( 440 v phase to phase 50-60 hz) that can run a 3hp induction motor.
    I am an Automation engg. from Mech. background and I have been looking for this circuit from a long time. it happens in VFD but they are too costly for the product that we are planning. Will really appreciate your help in it.

    • Thank you Abu-Hafss,

      That's very impressive and this will be quite handy for all the readers out there who may be trying to build the above circuit successfully.
      I'll update the corrected images in the above article soon

    • Thanks for uploading my findings.

      However, this line

      "Though the rectified output is not consistent but, it is quite acceptable."

      should be mentioned at the end.

  7. Hi Swagtam

    I needed a 15VAC 3-phase supply to test 3-phase rectifiers. I simulated this circuit the other day but failed to get proper results. Today, I made it work.

    IC A2 and resistors connected to pin 6 could be eliminated. The resistor between pin 7 and 9 could be connected between the main input and pin 9. Phase-1 output can be collected from the original AC input. Phase 2 and 3 can be collected as indicated in the circuit.

    https://dl.dropboxusercontent.com/u/20969135/Screenshot%202014-11-22%2000.58.38.png

    However, my actual requirement could not be fulfilled. When these 3 phases are connected to a 3-phase rectifier, the wave form of phase 2 and 3 gets disturbed. I tried with the original circuit, in that case all three phases gets disturbed 🙁

    https://dl.dropboxusercontent.com/u/20969135/Screenshot%202014-11-22%2001.00.40.png

    Any suggestions??

  8. R1 = (1.732 x 106) / (6.28 x F x C1). Hello sir. Thanks for very useful info. From the formula, may i know what are 1.732, 106 and 6.28 represent for?

  9. I have a pcb which convert 3 phase into 5vdc but i am weak in reverse engineering.. could you suggest me the simple way for tracing..

    • you can try this circuit:

      4.bp.blogspot.com/-MR2QAcISl4I/U9z3BuwZ6KI/AAAAAAAAHyw/e1IE6kxm8VA/s1600/3+phase+to+DC.png

      connect a 5V adapter such as a cell phone charger across the points "load" for getting the required 5V out

  10. hey.. is this possible convert 3 phase to 5vdc without transformer… and by using opamp..
    if yes please share …

  11. If I input a square wave with 30Hz, then after passing this circuit become 3 phase square wave? and will the frequency 30Hz changed???

  12. hi swagatam, please i want to know if i can drive a three phase washing machine motor with your Three Phase Inverter Circuit and also i want the motor to run at 8000-12000 RPM

  13. the zener diodes r just to clip odd the above unwanted waveform and make the sine wave lyk a square wave so it can be taken as a clock pulse

  14. i m trying to make a project which includes the controlling of elevator for 3 floor building, undervoltage and over voltage protection circuit and the three phase detection and protection circuit, well i hav made the controlling and o.v and u.v protection circuit but i am now stuck on this three phase detection and correction circuit??

    • I'll try to find some other circuit which can create artificial 3-phase signals that you can use for confirming with your detector stage.

    • the simplest method would be to take a small 3-phase motor and rotate it by coupling it to another motor (by belt or pulley)…once it starts rotating a three phase AC could be achieved across the three wires of the motor.

  15. also i have shared a link previous a circuit of 3 phase phase detection circuit
    wich has 10v zener diode , so shold i change it to 5v zener diode???

    • I haven't yet studied the circuit yet, if you can tell the role of the zener in the circuit then I can suggest whether it needs a change or not

    • I need a 3 phase pure sine signal
      as an input for the three phase detection circuit
      also try to study my phase detection circuit
      it wil just take a matter of minutes
      4 u
      also the output of the above circuit is non sinusoidal
      but i need threephase pure sine

  16. also when i measure the voltage across capacitor with multimeter i m getting voltage of 12 v but its d.c. not a.c so now what to do??

    • Hi harshal,

      you will need an oscilloscope to confirm the outputs, there's no other method of confirming an AC sine output with 120 degree phase shifts.

    • i checked it swagat. but i m not getting a pure sine output also when i m measuring it with the multimeter the output i m getting voltages for both d.c .and a.c
      i saw harmonics in the output so couldnt measure the phase sequence
      please help me
      also the resistance value decreased from 10 K to 8.5 K
      so should i change the resistances???
      n how to give ground to that single phase source ??

    • do u have whatsapp messenger so that i can directly be in your contact this will also ease my time as my project dead time is last of april month
      ???my mobile no. is +918460285967
      harshal sharma

    • In the meter it will only show RMS values, 12V in AC range and 6V in DC range.

      Actually the above circuit is not my design and I have not tested it practically, so it will be difficult for me to troubleshoot the circuit correctly.

      sorry I do not have a whatsapp account.

  17. Hey swagatam. I want to use this circuit for ac induction motor, please tell me if this circuit is working well. Also I want to know if anyone has build this circuit, thanks and please reply sooners

  18. Sir,

    How do we generate -12V to connect to pin # 11. And I suppose all the numbers indicated on A1–A4 is the pin numbers of the respective IC.

    • Jagan, you will need a dual power supply for that, you can easily make a dual power supply by using a center tap transformer or by using a resistive network with a 24V single supply.

      Yes those indicate the IC pin numbers.

    • Jagan ull need to make a dual supply using a centered tapped transformer of 220/15 -0-15 V AND USING 7912 IC u can get -12 volt supply

    • hi swagatam, i m really thankful to you coz of ur quick response to me
      one last question i need to know the use of 0.1 microfarad 400v capacitor y to use it with the input?? is it necessary ??after using this capacitor should i hav to step down the voltage or i can directly connect the input to the supply

    • Hi Harshal,
      with a 0.1uF cap in series you can provide the supply from the mains directly, however it would be rather better to eliminate the capacitor and provide the input from a 0-12V transformer, this would kepp the circuit isolated and ensure safety from mains lethal voltages

    • Hi Harshal,

      Make the above circuit and confirm whether you are getting the 120 degrees phase shifts or not by applying a 12V sine AC at the input…..once it's confirmed you can use it with this circuit for the detection.

      you will need an oscilloscope for confirming this.

  19. in the above circuit what will be the input source i mean what rating
    i used it with the230V SINGLE PHASE SUPPLY
    and the circuit burn out

    • Hi Harshal, since the circuit is 12V operated, the input should also be stepped down to 12V AC signal. You can do it by connecting a 0.1uF/400V capacitor in series with the input 10k resistor.

      THe outputs will then require half driver circuits to convert the relevant small signal phase shifts into 220V 3-phase AC.

  20. hey gud morning swagatam , i have made the three pulse generator , now its shown a single phase source as an input ,from where ill get this single phase source directly from the supply ??
    if yes , i did that the the 1st resistor burn out
    please help me

  21. sir i would like to ask you one question??
    i have made a three phase detection circuit in which if the supply goes from RYB TO RBY the circuit detects and gives signal to the relay
    but i have one doubt
    how should i connect the three phase supply as an input to the circuit
    i can not connect directly
    i have to create a signal of it
    so how will i make that signal which is beyond my knowledge
    i can mail you my circuit through gmail
    my id is harshal.sharma055@gmail.com
    please help me

  22. Thank you very much sir,
    Now just how do we connect these three outputs transistors (MOSFETs) and then to a transformer to realize a usable three phase 380V phase to phase that can be used to power motors?

    • In your case there are 3 solutions one described by Mohammad junaid.
      2nd is to to 3 phase a.c. supply to d.c. supply then again converting it to single phase a.c. supply from d.c. but it is costly.
      3rd on is by replaceing old 3phse alternor with new one single phase alternator.
      may be 2nd solution is more costly by 1st or 3rd solution.
      but before thinking about implemention on any suggesion i advise you to download and read information about preinstalled 3 phase alternator may by its output winding is
      star ( Y ) conneted then there is a nutral or common terminal in its connection box.

  23. hi sir good day. I'm here again. i have a 3 phase genset(standby generator} i think it was rated 1.5-2kw 440v. My problem is i only need is 1 phase 220v output for my needs can you help me design a circuit to make it 1 phase output. Thank you for your effort of doing this.

    • Hi Edalcore,

      I am sorry I don't any verified approach to do this, so it might be dangerous to suggest something which hasn't been confirmed by me.

    • Dear edalcor zuproc!
      It is possible but only by using a transformer, if your generator has DELTA output, you would require a Delta-Wye Connection three phase transformer with a common neutral on its output to use it for single phase.. (Verified Method)
      You may ask for its calculations if you want to design it..!

    • Hello Swagatam Majumdar…!
      I need your kind help please, can you please provide me a frequency converter circuit to convert 220V 50 Hz to 220V 60 Hz for a load of about 5A at 220V using oscillations or any other method using MOSFETS or IGBT's…. please help me regarding this…!!!
      plz plz

    • Hello Muhammad Junaid,

      VFD is a very complex circuit, so I don't think it would be possible for me, I'll try though, if I succeed then will surely post it for you.

    • 220V 50 Hz to 220V 60 Hz i would say just make from 220 AC –220 DC and after make half bridge mosfet or igbt pulsing on 60 Hz

  24. Thank you for the quick reply. I am a proud member of this blog. I can not wait to see the day passing without me visiting this site. I will try the mechanical concept, for the convertion of a car alternator to dc motor. Thank you once again.

  25. You are really helping . sir, Is it possible to convert car alternator to dc motor without PIC? if yes, I need your help on the circuitry. thank you



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