Transistor Amplifier for PWM output

indulis said:

Is there a load? Don't forget that "PWM" signal will just peak charge any capacitance on the output and hold it waiting for paracitics to discharge it. You can't just set a certain duty cycle and expect a certain voltage... other considerations come into play.

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Yes. I've done it. My problem is solved after connecting the load. I tried with a 47ohm resistor at first, then replaced with the real lamp. now I'm able to control the voltage from 0 to 4.95V, which is all that I wanted. I'm using TIP127.

Now the PWM frequency is 20KHz. So, I'd need an RC low-pass filter to input them to ADC. What should be the cut-off frequency?