Author Topic: effect of frequency on filter output amplitude  (Read 942 times)

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Offline Simon

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effect of frequency on filter output amplitude
« on: April 21, 2013, 09:11:51 pm »
I'm doing a PWM control circuit. The motor it will control will take the pwm signal and control the fan accordingly. Now I'm using an arduino and the standard frequency is 489 Hz whereas my motor manufacturer wants the PWM signal to be 50-150Hz.

Looking at the motor datasheet the input circuitry is a low pass filter, 127K series resistor, 100nF parallel capacitor, cutoff frequency 12.5 Hz, so I'm guessing that anything like a 50-150Hz square wave will just produce a DC(ish) voltage output ? but what will happen if the frequency is higher ? the capacitor will behave like a resistor to the signal frequency so would vary it's impedience based on the frequency but that makes no sense because 50-150 is a 1-3 range so the smoothed voltage would vary by 3 times which would seriously upset the fan.

So basically, I think I'm safe with the default arduino PWM frequency ? (This particular manufacturer is well known for churning out incorrect limitations on it's datasheets).

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