I would like to build a simple RC filter for a PWM input. I have used this tool: http://sim.okawa-denshi.jp/en/PWMtool.php

to get the math done :)

I have a 1000 hz pwm input, I can stand to a rather high settling time. I end with a 2k resistor and 100u capacitor.

With this params (2k 100u at 1000hz) I got 0.006 ripple 0.460s settling time that are fine for me, I think.

Now, back to question: Is there ny difference for capacitor type with a simple 1 resistor + 1 capacitor or i can use any type of capacitor? (there is no polarity inversion or anything, so I can use electrolytic as well)

Does the type of capacitor affect the RC filter at all? Is it the correct approach to try to have low resistor to have low impedance on the output and having a big capacitor instead of the opposite?


Why not a use a 20 kohm resistor and a 10 uF capacitor? These values seem more reasonable and likely take up much less room for a given voltage amplitude. There is also a good chance that a 10 uF capacitor will be available in a tighter tolerance than a 100 uF electrolytic type.

A larger capacitor will have a greater ESR (effective series resistance) and this might make the high frequency performance unacceptable for some applications. Also, the self resonant frequency (due to ESL or effective series inductance) will probably be significantly lower for a higher value capacitor and also upset the "purity" of the low pass filter.


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