• Filters are the electronic circuits used along with rectifiers in order to get a pure ripple free dc voltage.

• Till now we have seen that from all the rectifiers we get a "pulsating" dc voltage as shown in Fig.(a).

• But this is not what we want. What we want is a pure dc waveform as shown in Fig. (b).

• In order to obtain it we use filters. A filter is connected at the output of the rectifier as shown in Fig. (c).

• We can connect a filter at the output of any type of rectifier. (HWR,FWR or bridge).

The filter circuits use resistor, capacitor and inductors, Therefore they are called as passive filters