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PWM to DC converter.

Discussion in 'Robotics & Mechatronics' started by kaarvannan, Dec 11, 2011.

  1. kaarvannan

    kaarvannan New Member

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    I have a motor controller that outputs a Pulse Width Modulated signal. Though, this works just fine, it induces substantial amount of noise on nearby wires. So I was hoping to convert the PWM signal to an analog DC signal. The PWM signal is 60HZ and 36V. i.e. to run the motor at 50% of its speed I would have to send a 18V signal. What is the best way to get this done, with good response time and less noise. Thank you for your help.
     
  2. koolguy

    koolguy Active Member

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    What does this mean?
     
  3. kaarvannan

    kaarvannan New Member

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    sorry about that. I will try to explain this in a different way. This circuit will go in-between a motor controller (that outputs pulse width modulated signal) and a DC motor. So, instead of a square wave reaching the DC motor, I want a linear voltage to reach it. So if the PWM signal is on/high for 10% of the time, the corresponding linear voltage should be 3.6V(10% 0f 36V). thus producing the same effect on the DC motor. hope I made myself clear!
     
  4. dave

    Dave New Member

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  5. koolguy

    koolguy Active Member

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    If the motor is DC and you want to Run the maximum speed so why are you using PWM controller?? directly give the supply of it rated one.
     
  6. pilko

    pilko Member

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    What you are trying to do is filter the output of the PWM controller to give a smooth DC to the motor.
    What is the motor current?
     
  7. pilko

    pilko Member

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    Your filter will look like this, but the values will depend on the frequency, voltage, current and how much ripple you can accept.
     

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  8. kaarvannan

    kaarvannan New Member

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    I do not want to run the maximum speed. I want to be able to controll the speed, that is why i use the PWM controller.
     
  9. kaarvannan

    kaarvannan New Member

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    Thanks Pilko. The frequency is 60Hz, the voltage is 36V and the current rating of my motor is 3 Amps. I would like to keep the ripple current as low as possible. What are the values that you would suggest?
     
  10. pilko

    pilko Member

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    Are you sure the PWM frequency is 60Hz, if it is, you will need a very large inductor.
     
  11. kaarvannan

    kaarvannan New Member

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    You are right. It is not 60Hz. Its actually 20KHz.
     
  12. pilko

    pilko Member

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    Try This
     

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  13. kaarvannan

    kaarvannan New Member

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    Thank you Pilko. Will try it and let you know how it works out.
     
  14. pilko

    pilko Member

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    Make sure the coil is rated for at least 10A. And the caps are Electrolytic 100V
     
  15. kaarvannan

    kaarvannan New Member

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    I need the motor to go forward and reverse. So the polarity of the input will change. Can I fix this just by adding another inductor on the bottom rung of the circuit?
     
  16. pilko

    pilko Member

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    Is your controller an H Bridge type --- does it do the reversing?
     
  17. pilko

    pilko Member

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    What is your motor type, Stepper, Servo or Brushed DC?
     
  18. kaarvannan

    kaarvannan New Member

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    we use a servo motor. Could you please email your response to the address I mentioned in the private message I sent you. Thanks.
     
  19. pilko

    pilko Member

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    I do not respond to requests for help via private messages.
    If you need further help, ask on the forum so others may participate if they wish.
     
  20. kaarvannan

    kaarvannan New Member

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    ok then. To answer your previous question. we use a servo motor. so what changed should i make to your original circuit to be able to drive the motor in both the directions.
     
  21. pilko

    pilko Member

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    Is the PWM you are trying to smooth, the main supply to the motor or the trigger pulses, if the latter, the pulses are required for positioning of the servo.
     

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