Semiconductor diodes are widely used to convert most alternating current (AC) signals, typically at 60 or 50 Hz, into direct current (DC) signals in the electronics industry. Electronic devices can be powered by the DC signal instead of batteries. In a rectifier, the circuit that transforms AC signals into DC signals is composed of an interlocking arrangement of diodes.

DERF Electronics has put together a nice introduction on Bridge Rectifiers - enjoy!