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Silicon controlled rectifier
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<p>A silicon controlled rectifier or semiconductor controlled rectifier (SCR) is a four-layer <a href="/facts/Solid-state_electronics/US0Qbq28">solid-state</a> <a href="/facts/Electric_current/Dc1xdnUX">current</a>-controlling device. The name "silicon controlled rectifier" is <a href="/facts/General_Electric/bBm5CzVY">General Electric</a>'s trade name for a type of <a href="/facts/Thyristor/DYPV2ftl">thyristor</a>. The principle of four-layer p–n–p–n switching was developed by Moll, Tanenbaum, Goldey, and Holonyak of <a href="/facts/Bell_labs/fKP5Gk0H">Bell Laboratories</a> in 1956. The practical demonstration of silicon controlled switching and detailed theoretical behavior of a device in agreement with the experimental results was presented by Dr Ian M. Mackintosh of Bell Laboratories in January 1958. The SCR was developed by a team of <a href="/facts/Power_engineering/0EWEmAVW">power engineers</a> led by Gordon Hall and commercialized by Frank W. "Bill" Gutzwiller in 1957. </p><p>Some sources define silicon-controlled rectifiers and thyristors as synonymous while other sources define silicon-controlled rectifiers as a <a href="/facts/Subset/SJGERmbA">proper subset</a> of the set of thyristors; the latter being devices with at least four layers of alternating <a href="/facts/N-type_semiconductor/d9GPL5tV">n-</a> and <a href="/facts/P-type_semiconductor/d9GPL5tV">p-type material</a>. According to Bill Gutzwiller, the terms "SCR" and "controlled rectifier" were earlier, and "thyristor" was applied later, as usage of the device spread internationally. </p><p>SCRs are unidirectional devices (i.e. can conduct current only in one direction) as opposed to <a href="/facts/TRIAC/HRvWQkja">TRIACs</a>, which are bidirectional (i.e. charge carriers can flow through them in either direction). SCRs can be triggered normally only by a positive current 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. </p>