electronic rectifiers (3679-er)

overview of electronic rectifiers (3679-er)

— a rectifier is an electrical device that converts alternating current (ac), which periodically reverses direction, to direct current (dc), which flows in only one direction. the process is known as rectification. physically, rectifiers take a number of forms, including vacuum tube diodes, mercury-arc valves, copper and selenium oxide rectifiers, semiconductor diodes, silicon-controlled rectifiers and other silicon-based semiconductor switches. historically, even synchronous electromechanical switches and motors have been 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". rectifiers have many uses, but are often found serving as components of dc power supplies and high-voltage direct current power transmission systems. rectification may serve in roles other than to generate direct current for use as a source of power. as noted, detectors of radio signals serve as rectifiers. in gas heating systems flame rectification is used to detect presence of a flame.

a silicon controlled rectifier (scr) or semiconductor-controlled rectifier is a four-layer solid-state current-controlling device. the name "silicon controlled rectifier" is general electric's trade name for a type of thyristor. scrs are unidirectional devices (i.e. can conduct current only in one direction) as opposed to triacs, which are bidirectional (i.e. current can flow through them in either direction). scrs can be triggered normally only by currents going into the gate as opposed to triacs, which can be triggered normally by either a positive or a negative current applied to its gate electrode.