Need for filters
1) Output of all rectifiers is pulsating dc voltage and most of citcuits which work on dc requires pure dc voltage.
2) So in order to get pure dc waveform, filters are connected at the output of rectifier to remove the ripple.
3) Thus filters are electronic circuits used alongwith rectifier in order to get a pure ripple free dc voltage.
Types of filters
1) Capacitor input filter(Shunt capacitor filter)
2) Choke input filter(series inductor filter)
3) LC filter
4) π Filter
5) RC filter