PWM to DC converter.

[kaarvannan]

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.

 

[koolguy]

to an analog DC signal.

What does this mean?

 

[kaarvannan]

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!

 

[koolguy]

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.

 

[pilko]

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?

 

[pilko]

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

 

[kaarvannan]

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.

 

[kaarvannan]

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?

 

[pilko]

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

 

[kaarvannan]

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

 

[pilko]

Try This

 

[kaarvannan]

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

 

[pilko]

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

 

[kaarvannan]

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?

 

[pilko]

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

 

[pilko]

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

 

[kaarvannan]

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

 

[pilko]

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.

 

[kaarvannan]

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.

 

[pilko]

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.