1. The process of converting an alternating voltage (or current) to a direct voltage (or current) is called rectification. A circuit or device that is used to convert an alternating voltage (or current) to a direct voltage (or current) is called a rectifier. A rectifier produces a unidirectional but pulsating voltage from an alternating voltage.
2. When an alternating voltage is applied across a pn-junction diode, the diode is forward-biased and reverse-biased during alternate half cycles.
3. During the half cycle when the diode is forward- – biased, it conducts. Therefore, there is a current through it from the p-region to the n-region.
4. During the next half cycle, it is reversebiased and does not conduct. Therefore, current passes only in one direction through the circuit. This way, a pn-junction diode acts as a rectifier.