PWM

[mjoco]

Hello!

I want to ask something about the Pulse Width Modulation. Which voltage value is more important? Average (V*duty) or RMS (V*sqrt(duty))? If I calculate the work, then the PWM's RMS value represents the equal DC voltage. By contrast every one uses the average voltage formula - etc. 10V, 50% PWM equals 5V DC.
What's the truth?

Best Regards
mjoco

 

[itsmoked]

Since pwm is generally a square wave the average is what's used.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[DHambley]

It really depends on what parameter you are interested in. If you are interested in average output voltage, it's Vin*duty. If you are interested in the equivalent rms voltage of a square wave, then it's Vin*sqrt(duty). The resulting power in a resistive element would be based on rms voltage. Since you are in the motor forum though, I am assuming that you would be applying a PWM voltage onto an inductive element. Average voltage is what you are interested in then.

 

[mjoco]

Hi!

Thanks for the quick reply!
I know the DC motor is kind of a "low pass filter", it suppresses the AC component of the PWM signal. The rest is the DC component what equals the average value of the PWM. Is this correct? So, this is the reason why I should use the Vin*Duty formula by motor control instead of Vin*sqrt(Duty)?

Best Regards