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{{short description|Four-layer solid-state current-controlling device}}▼
{{more citations needed|date=December 2019}}
▲{{short description|Four-layer solid-state current-controlling device}}
{{Infobox electronic component
| name
▲|image = Image:SCR de potencia.jpg
▲|image_size =
▲|caption = Silicon controlled rectifier
| working_principle = Ian M. Mackintosh ([[Bell labs|Bell Laboratories]])▼
▲|type = [[Electronic component#Active components|Active]]
▲|working_principle = Ian M. Mackintosh ([[Bell labs|Bell Laboratories]])
▲|invented = Gordon Hall and Frank W. "Bill" Gutzwiller
▲|first_produced = [[General Electric]], 1957
▲|symbol = [[Image:Thyristor circuit symbol.svg|150px]]
▲|pins = [[Anode]], [[gate]] and [[cathode]]
}}
[[File:Thyristor layers.svg|thumb|SCR 4-layer (p-n-p-n) diagram]]
A '''silicon controlled rectifier''' or '''semiconductor controlled rectifier''' is a four-layer [[solid-state electronics|solid-state]] [[Electric current|current]]-controlling device. The name "silicon controlled rectifier" is [[General Electric]]'s trade name for a type of [[thyristor]]. The principle of four-layer p–n–p–n switching was developed by Moll, Tanenbaum, Goldey, and Holonyak of [[Bell labs|Bell Laboratories]] in 1956.<ref>{{Cite journal|last1=Moll|first1=J.|last2=Tanenbaum|first2=M.|last3=Goldey|first3=J.|last4=Holonyak|first4=N.|date=September 1956|title=P-N-P-N Transistor Switches|journal=Proceedings of the IRE|language=en-US|volume=44|issue=9|pages=1174–1182|doi=10.1109/jrproc.1956.275172|s2cid=51673404|issn=0096-8390}}</ref> 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.<ref>{{Cite book|url=https://books.google.com/books?id=g9Y_DQAAQBAJ|title=Properties and Applications of Transistors|last=Vasseur|first=J. P.|date=2016-06-06|publisher=Elsevier|isbn=9781483138886|language=en}}</ref><ref>{{Cite news|url=http://news.bbc.co.uk/1/hi/sci/tech/4449711.stm|title=Law that has driven digital life|last=Twist|first=Jo|date=2005-04-18|work=BBC News|access-date=2018-07-27|language=en-GB}}</ref> The SCR was developed by a team of [[Power engineering|power engineer]]s led by Gordon Hall
<ref>{{cite web|last=Ward|first=Jack|title=The Early History of the Silicon Controlled Rectifier|url=http://www.semiconductormuseum.com/Transistors/GE/OralHistories/Gutzwiller/Gutzwiller_Page6.htm|access-date=12 April 2014|page=6}}</ref> <ref>{{cite web |title=Semiconductors: Thyristors and more |url=https://edisontechcenter.org/semiconductors.html |publisher=Edison Tech Center}}</ref>
<ref>{{cite web |title=SCR is 50 Years Old |url=https://ieeemilestones.ethw.org/w/images/5/52/Milestone_Reference_1-SCR_50_Yrs_Old_Owen_IASMag_2007.pdf |publisher=IEEE Industry Applications Magazine}}</ref>
<ref>{{cite news |last1=Mungenast |first1=J. E. |title=The SCR Revolution |url=https://www.rfcafe.com/references/electronics-world/scr-revolution-electronics-world-february-1966.htm |website=RF Cafe |publisher=General Electric Co.}}</ref>
and commercialized by Frank W. "Bill" Gutzwiller in 1957.
Some sources define silicon-controlled rectifiers and thyristors as synonymous<ref>{{Cite book|title=Standard Handbook of Electronic Engineering, 5th Edition|last1=Christiansen|first1=Donald|last2=Alexander|first2=Charles|last3=Jurgen|first3=Ronald|date=2005|publisher=Mcgraw-hill|isbn=9780071384216|language=en}}</ref> while other sources define silicon-controlled rectifiers as a [[Subset#Definitions|proper subset]] of the set of thyristors; the latter being devices with at least four layers of alternating [[N-type semiconductor|n-]] and [[P-type semiconductor|p-type material]].<ref>
[[International Electrotechnical Commission]] 60747-6 standard
</ref><ref>{{Cite book|title=The Electrical Engineering Handbook, Second Edition|last=Dorf|first=Richard C.|date=1997-09-26|publisher=CRC Press|isbn=9781420049763|language=en}}</ref> According to Bill Gutzwiller, the terms "SCR" and "controlled rectifier" were earlier, and "thyristor" was applied later, as usage of the device spread internationally.<ref>{{cite web|last=Ward|first=Jack|title=The Early History of the Silicon Controlled Rectifier|url=http://www.semiconductormuseum.com/Transistors/GE/OralHistories/Gutzwiller/Gutzwiller_Page7.htm|access-date=12 April 2014|page=7}}</ref>
SCRs are unidirectional devices (i.e. can conduct current only in one direction) as opposed to [[TRIAC]]s, 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.
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# gate triggering
# ''dv''/''dt'' triggering
#
# light triggering
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Temperature triggering occurs when the width of depletion region decreases as the temperature is increased. When the SCR is near VPO a very small increase in temperature causes junction J2 to be removed which triggers the device.
== Simple SCR
[[File:Simple scr circuit.png|thumb|317x317px|A simple SCR circuit with a resistive load]]
A simple SCR circuit can be illustrated using an AC voltage source connected to a SCR with a resistive load. Without an applied current pulse to the gate of the SCR, the SCR is left in its forward blocking state. This makes the start of conduction of the SCR controllable. The delay angle α, which is the instant the gate current pulse is applied with respect to the instant of natural conduction (ωt = 0), controls the start of conduction. Once the SCR conducts, the SCR does not turn off until the current through the SCR, i<sub>s</sub>, becomes negative. i<sub>s</sub> stays zero until another gate current pulse is applied and SCR once again begins conducting.<ref>{{Cite book|title=Power Electronics: A First Course|last=Mohan|first=Ned|publisher=Don Fowley|year=2012|isbn=978-1-118-07480-0|location=United States|pages=230–231}}</ref>
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SCRs are mainly used in devices where the control of high power, possibly coupled with high voltage, is demanded. Their operation makes them suitable for use in medium- to high-voltage AC power control applications, such as [[Dimmer|lamp dimming]], power regulators and motor control.
SCRs and similar devices are used for rectification of high-power AC in [[high-voltage direct current]] power transmission. They are also used in the control of welding machines, mainly [[
▲They are also used in the control of welding machines, mainly [[Gas tungsten arc welding|GTAW (gas tungsten arc welding)]] and similar processes. It is used as switch in various devices. [[Pinball#1970s: Solid-state electronics and digital displays introduced|Early Solid-State Pinball]] machines made use of these to control lights, solenoids, and other functions digitally, instead of mechanically, hence the name, Solid-state.
Other applications include power switching circuits, controlled rectifiers, speed control of DC shunt motors, SCR crowbars, computer logic circuits, timing circuits, and inverters.
==Comparison with SCS==
A silicon-controlled switch (SCS) behaves nearly the same way as an SCR; but there are a few differences
SCSs are useful in practically all circuits that need a switch that turns on/off through two distinct control pulses. This includes power-switching circuits, logic circuits, lamp drivers,
==Compared to TRIACs==
A [[TRIAC]] resembles an SCR in that both act as electrically controlled switches. Unlike an SCR, a TRIAC can pass current in either direction. Thus, TRIACs are particularly useful for AC applications. TRIACs have three leads: a gate lead and two conducting leads, referred to as MT1 and MT2. If no current/voltage is applied to the gate lead, the TRIAC switches off. On the other hand, if the trigger voltage is applied to the gate lead, the TRIAC switches on.
==See also==
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