DC power supply:-

• The DC power supply has to provide a smooth, constant dc voltage. To convert input AC signal to required constant dc voltage the d.c. power supply consists of various circuits as shown in figure below.

Need for Filters:-

• The output of a rectifier contains dc component as well as ac component. The presence of ac component is undesirable and therefore must be removed from the rectifier output. The circuit which removes the unwanted ac component is called filter. Depending upon the circuit elements used in the filters, the filters are classified into following categories.

1. Inductor filter or L filter
2. Capacitor filter or C filter
3. Inductor Capacitor filter or LC filter
4. π filter

• Inductors used in filter circuits are always connected in series with the load. Inductors act as short circuit for d.c. and open circuit for a.c. Thus inductor passes d.c. through it and blocks a.c.
• Capacitors used in filter circuits are always connected in parallel to the load. Capacitors act as open circuit for d.c. and short circuit for a.c. Thus Capacitor blocks d.c. through it and passes a.c through it.The passed a.c. through the capacitor C is passed to the ground and blocked d.c. is produced as output.