I'm working on designing a passive LPF to use with the PIC PWM output. I have the frequency set at 20Khz, 3.3V right now just for testing purposes. First I need some clarification into my understanding of how a LPF should really work.
I understand that we want to eliminate the high frequencies, so does that mean that the lower the cut-off frequency is from the LPF the more accurate the average output will be.
For example I have a LPF with R = 1K and C = 1uF. This will be a Fc = 1/(2piRC) = 159Hz.
I've attached what the simulation looks like for two different scenarios, the second one uses 100nF for C. I've done a couple of different simulations and noticed that the ripple of the output is worst with with lower capacitance, but rise time is faster. With higher resistance the ripple is better, but longer rise time for vout. So my question is how low of a cut-off frequency is a "good" cut-off. Any input will help. I've been reading a lot a still don't really get, but I think I'm almost there.