The capacitor-input filter, as well called pi filter because of its shape which looks like the Greek letter pi, is a sort of electronic filter. Filter circuits are employed to remove not wanted or not desired frequencies from a signal.
A common capacitor input filter contains a filter capacitor C1, associated across the rectifier output, an inductor L, in series and other filter capacitor, C2 associated across the load, RL. A filter of this sort is designed for use at a specific frequency, usually fixed by the AC line frequency and rectifier configuration. While used in this service, filter performance is frequently characterized via its regulation and ripple.
1. The capacitor C1 proposes low reactance to the AC (Alternating current) component of the rectifier output whereas it offers infinite reactance to the DC (direct current) component. The effect of it is the capacitor shunts an appreciable amount of the AC component whereas the DC component continues its journey to the inductor L.
2. The inductor L purposes high reactance to the AC (Alternating current) component but it offers approximately zero reactance to the DC component. The result of it is the DC component flows through the inductor whereas the AC component is blocked.
3. The capacitor C2 bypasses the AC component that the inductor had failed to block. As a result just only the DC component appears across the load RL.