A device that passes current only in the forward direction and can therefore be used as an a.c. to d.c. converter. A single device usually suppresses or attenuates alternate half-cycles of the alternating-current input (see half-wave rectifier circuit). Full-wave rectifiers usually contain two devices in a back-to-back arrangement. The most common type of rectifier is the semiconductor diode. The rectification efficiency of any rectifier is the ratio of the direct-current output power to the alternating-current input power.
The output of a rectifier consists of a unidirectional current that rises to a maximum value periodically; this value corresponds to the peak value of the alternating-current input. The output is usually smoothed by a smoothing circuit before being applied to the load in order to reduce the amount of ripple. The fluctuating output can be considered as a steady d.c. component with an a.c. component superimposed on it. A portion of the ripple is sometimes due to the rectifier leakage current, i.e. alternating current that flows through the rectifier without being rectified.