Hi all,

I'm trying to build a low-pass RC filter, but I'm not sure if I've picked out the right values for the resistor and capacitor. I'm trying to extract the sine wave from a sine wave modulated PWM. The PWM switches at 20kHz and the sine wave is anywhere between 1 to 100 Hz. I want to use a 10k ohm resistor and a 20nF capacitor. Do these values sound ok?

Thanks!

 

Hello,

The formula for a RC filter is :

If you use the 10K and 20 nF you will get a cutoff frequency of about 800 Hz.

Greetings,
Bertus

 

Right, so will 800Hz be sufficient to extract the sine wave?

 

Hello,

A normal RC filter has a decay of 6 dB / octave.
The 20 kHz will be damped with about 30 dB. (estimated).

The resulting sinewave will be fair enough.

Greetings,
Bertus