A rectifier is an
electrical device that converts
alternating current to
direct current or at least to current with only positive value, a process known as rectification. Rectifiers are used as components of
power supplies and as
detectors of
radio signals. Rectifiers may be made of
solid state diodes,
vacuum tube diodes,
mercury arc valves, and other components.
A circuit which performs the opposite function (converting DC to AC) is known as an
inverter.
When only one diode is used to rectify AC (by blocking the negative or positive portion of the
waveform), the difference between the term diode and the term rectifier is merely one of usage, i.e., the term rectifier describes a diode that is being used to convert AC to DC. Almost all rectifiers comprise a number of diodes in a specific arrangement for more efficiently converting AC to DC than is possible with only one diode. Before the development of silicon semiconductor rectifiers,
vacuum tube diodes and
copper(I) oxide or
selenium rectifier stacks were used.
Early radio receivers, called
crystal radios, used a "
cat's whisker" of fine wire pressing on a crystal of
galena (lead sulfide) to serve as a point-contact rectifier or "
crystal detector". In gas heating systems flame rectification can be used to detect a flame. Two metal electrodes in the outer layer of the flame provide a current path and rectification of an applied alternating voltage, but only while the flame is present
