Capacitor-input filter


Capacitor-input filter

The capacitor-input filter, also called "Pi" filter due to its shape that looks like the Greek letter pi, is a type of electronic filter. Filter circuits are used to remove unwanted or undesired frequencies from a signal.

A typical capacitor input filter consists of a filter capacitor C1, connected across the rectifier output, a choke L, in series and another filter capacitor connected across the load.

# The capacitor C1 offers low reactance to the AC component of the rectifier output while it offers infinite reactance to the DC component. As a result the capacitor bypasses an appreciable amount of the AC component while the DC component continues its journey to the choke L
# The choke L offers high reactance to the AC component but it offers almost zero reactance to the DC component. As a result the DC component flows through the choke while the AC component is blocked.
# The capacitor C2 bypasses the AC component which the choke had failed to block. As a result only the DC component appears across the load.


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