Question

Why do we need filters in a power supply?

Answer 1

A rectifier circuit produces a DC output from an AC input but the output waveform is still the positive or negative side of the original AC waveform, usually a sine wave in domestic power circuits. To use this in most devices requiring a DC input the waveform has to be filtered so the output voltage remains at as near a constant level as possible especially in circuits where a ripple frequency could affect the operation of the device. For instance, an audio amplifier without filtering on the power supply would have a huge amount of 50 or 60 Hz hum in the output.