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A thyristor () is a
solid-state Solid state, or solid matter, is one of the four fundamental states of matter. Solid state may also refer to: Electronics * Solid-state electronics, circuits built of solid materials * Solid state ionics, study of ionic conductors and their use ...
semiconductor device A semiconductor device is an electronic component that relies on the electronic properties of a semiconductor material (primarily silicon, germanium, and gallium arsenide, as well as organic semiconductors) for its function. Its conductivity li ...
with four layers of alternating P- and N-type materials used for high-power applications. It acts exclusively as a bistable switch (or a latch), conducting when the gate receives a current trigger, and continuing to conduct until the voltage across the device is reversed biased, or until the voltage is removed (by some other means). There are two designs, differing in what triggers the conducting state. In a three-lead thyristor, a small current on its Gate lead controls the larger current of the Anode to Cathode path. In a two-lead thyristor, conduction begins when the potential difference between the Anode and Cathode themselves is sufficiently large (breakdown voltage). Some sources define
silicon-controlled rectifier A silicon controlled rectifier 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. The principle of four ...
(SCR) and thyristor as synonymous. Other sources define thyristors as more complex devices that incorporate at least four layers of alternating N-type and P-type substrate. The first thyristor devices were released commercially in 1956. Because thyristors can control a relatively large amount of power and voltage with a small device, they find wide application in control of electric power, ranging from light
dimmer A dimmer is a device connected to a light fixture and used to lower the brightness of the lighting, light. By changing the voltage waveform applied to the lamp, it is possible to lower the luminous intensity, intensity of the light output. Alt ...
s and electric motor speed control to
high-voltage direct-current A high-voltage direct current (HVDC) electric power transmission system (also called a power superhighway or an electrical superhighway) uses direct current (DC) for electric power transmission, in contrast with the more common alternating curre ...
power transmission. Thyristors may be used in power-switching circuits, relay-replacement circuits, inverter circuits, oscillator circuits, level-detector circuits, chopper circuits, light-dimming circuits, low-cost timer circuits, logic circuits, speed-control circuits, phase-control circuits, etc. Originally, thyristors relied only on current reversal to turn them off, making them difficult to apply for direct current; newer device types can be turned on and off through the control gate signal. The latter is known as a
gate turn-off thyristor A gate turn-off thyristor (GTO) is a special type of thyristor, which is a high-power (.e.g. 1200V AC) semiconductor device. It was invented by General Electric. GTOs, as opposed to normal thyristors, are fully controllable switches which can be ...
, or GTO thyristor. Unlike
transistor upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch e ...
s, thyristors have a two-valued switching characteristic, meaning that a thyristor can only be fully on or off, while a transistor can lie in between on and off states. This makes a thyristor unsuitable as an analog amplifier, but useful as a switch.


Introduction

The thyristor is a four-layered, three-terminal semiconductor device, with each layer consisting of alternating N-type or P-type material, for example P-N-P-N. The main terminals, labelled anode and cathode, are across all four layers. The control terminal, called the gate, is attached to p-type material near the cathode. (A variant called an SCS—silicon controlled switch—brings all four layers out to terminals.) The operation of a thyristor can be understood in terms of a pair of tightly coupled
bipolar junction transistor A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor, uses only one kind of charge carrier. A bipolar ...
s, arranged to cause a self-latching action: : Thyristors have three states: # Reverse blocking mode – Voltage is applied in the direction that would be blocked by a diode # Forward blocking mode – Voltage is applied in the direction that would cause a diode to conduct, but the thyristor has not been triggered into conduction # Forward conducting mode – The thyristor has been triggered into conduction and will remain conducting until the forward current drops below a threshold value known as the "holding current"


Function of the gate terminal

The thyristor has three p-n junctions (serially named J1, J2, J3 from the anode). When the anode is at a positive potential VAK with respect to the cathode with no voltage applied at the gate, junctions J1 and J3 are forward biased, while junction J2 is reverse biased. As J2 is reverse biased, no conduction takes place (Off state). Now if ''V''AK is increased beyond the breakdown voltage ''V''BO of the thyristor,
avalanche breakdown Avalanche breakdown (or avalanche effect) is a phenomenon that can occur in both insulating and semiconducting materials. It is a form of electric current multiplication that can allow very large currents within materials which are otherwise good ...
of J2 takes place and the thyristor starts conducting (On state). If a positive potential ''V''G is applied at the gate terminal with respect to the cathode, the breakdown of the junction J2 occurs at a lower value of ''V''AK. By selecting an appropriate value of ''V''G, the thyristor can be switched into the on state quickly. Once avalanche breakdown has occurred, the thyristor continues to conduct, irrespective of the gate voltage, until: (a) the potential ''V''AK is removed or (b) the current through the device (anode−cathode) becomes less than the holding current specified by the manufacturer. Hence ''V''G can be a voltage pulse, such as the voltage output from a
UJT A unijunction transistor (UJT) is a three-lead electronic semiconductor device with only one junction that acts exclusively as an electrically controlled switch. The UJT is not used as a linear amplifier. It is used in free-running oscillators, sy ...
relaxation oscillator In electronics a relaxation oscillator is a nonlinear electronic oscillator circuit that produces a nonsinusoidal repetitive output signal, such as a triangle wave or square wave. on Peter Millet'Tubebookswebsite The circuit consists of a feedba ...
. The gate pulses are characterized in terms of gate trigger voltage (''V''GT) and gate trigger current (''I''GT). Gate trigger current varies inversely with gate pulse width in such a way that it is evident that there is a minimum gate
charge Charge or charged may refer to: Arts, entertainment, and media Films * ''Charge, Zero Emissions/Maximum Speed'', a 2011 documentary Music * ''Charge'' (David Ford album) * ''Charge'' (Machel Montano album) * ''Charge!!'', an album by The Aqua ...
required to trigger the thyristor.


Switching characteristics

In a conventional thyristor, once it has been switched on by the gate terminal, the device remains latched in the on-state (''i.e.'' does not need a continuous supply of gate current to remain in the on state), providing the anode current has exceeded the latching current (''I''L). As long as the anode remains positively biased, it cannot be switched off unless the current drops below the holding current (''I''H). In normal working conditions the latching current is always greater than holding current. In the above figure ''IL'' has to come above the ''IH'' on y-axis since ''IL''>''IH''. A thyristor can be switched off if the external circuit causes the anode to become negatively biased (a method known as natural, or line, commutation). In some applications this is done by switching a second thyristor to discharge a capacitor into the anode of the first thyristor. This method is called forced commutation. Once the current through the thyristor drops below the holding current, there must be a delay before the anode can be positively biased ''and'' retain the thyristor in the off-state. This minimum delay is called the circuit commutated turn off time (''t''Q). Attempting to positively bias the anode within this time causes the thyristor to be self-triggered by the remaining charge carriers (
holes A hole is an opening in or through a particular medium, usually a solid body. Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in many fields of en ...
and
electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kn ...
s) that have not yet recombined. For applications with frequencies higher than the domestic AC mains supply (e.g. 50 Hz or 60 Hz), thyristors with lower values of ''t''Q are required. Such fast thyristors can be made by diffusing heavy metal
ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
s such as
gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile met ...
or
platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Platinu ...
which act as charge combination centers into the silicon. Today, fast thyristors are more usually made by
electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kn ...
or
proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
irradiation Irradiation is the process by which an object is exposed to radiation. The exposure can originate from various sources, including natural sources. Most frequently the term refers to ionizing radiation, and to a level of radiation that will serve ...
of the silicon, or by
ion implantation Ion implantation is a low-temperature process by which ions of one element are accelerated into a solid target, thereby changing the physical, chemical, or electrical properties of the target. Ion implantation is used in semiconductor device fab ...
. Irradiation is more versatile than heavy metal doping because it permits the dosage to be adjusted in fine steps, even at quite a late stage in the processing of the silicon.


History

The silicon controlled rectifier (SCR) or thyristor proposed by
William Shockley William Bradford Shockley Jr. (February 13, 1910 – August 12, 1989) was an American physicist and inventor. He was the manager of a research group at Bell Labs that included John Bardeen and Walter Brattain. The three scientists were jointly ...
in 1950 and championed by Moll and others at
Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company owned by mult ...
was developed in 1956 by power engineers at
General Electric General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable energ ...
(G.E.), led by Gordon Hall and commercialized by G.E.'s Frank W. "Bill" Gutzwiller. The
Institute of Electrical and Electronics Engineers The Institute of Electrical and Electronics Engineers (IEEE) is a 501(c)(3) professional association for electronic engineering and electrical engineering (and associated disciplines) with its corporate office in New York City and its operation ...
recognized the invention by placing a plaque at the invention site in Clyde, NY and declaring it an IEEE Historic Milestone.


Etymology

An earlier
gas-filled tube A gas-filled tube, also commonly known as a discharge tube or formerly as a Plücker tube, is an arrangement of electrodes in a gas within an insulating, temperature-resistant envelope. Gas-filled tubes exploit phenomena related to electric d ...
device called a
thyratron A thyratron is a type of gas-filled tube used as a high-power electrical switch and controlled rectifier. Thyratrons can handle much greater currents than similar hard-vacuum tubes. Electron multiplication occurs when the gas becomes ionized, pro ...
provided a similar electronic switching capability, where a small control voltage could switch a large current. It is from a combination of "THYRatron" and "
transISTOR upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch e ...
" that the term "thyristor" is derived.


Applications

Thyristors are mainly used where high currents and voltages are involved, and are often used to control
alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...
s, where the change of polarity of the current causes the device to switch off automatically, referred to as " zero cross" operation. The device can be said to operate ''synchronously''; being that, once the device is triggered, it conducts current in phase with the voltage applied over its cathode to anode junction with no further gate modulation being required, i.e., the device is biased ''fully on''. This is not to be confused with asymmetrical operation, as the output is unidirectional, flowing only from cathode to anode, and so is asymmetrical in nature. Thyristors can be used as the control elements for phase angle triggered controllers, also known as
phase fired controllers Phase-fired control (PFC), also called phase cutting or "phase angle control", is a method for power limiting, applied to AC voltages. It works by modulating a thyristor, SCR, triac, thyratron, or other such gated diode-like devices into and ou ...
. They can also be found in power supplies for
digital circuits Digital electronics is a field of electronics involving the study of digital signals and the engineering of devices that use or produce them. This is in contrast to analog electronics and analog signals. Digital electronic circuits are usual ...
, where they are used as a sort of "enhanced
circuit breaker A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by an overcurrent or short circuit. Its basic function is to interrupt current flow to protect equipment and to prevent the risk ...
" to prevent a failure in the power supply from damaging downstream components. A thyristor is used in conjunction with a
Zener diode A Zener diode is a special type of diode designed to reliably allow current to flow "backwards" (inverted polarity) when a certain set reverse voltage, known as the ''Zener voltage'', is reached. Zener diodes are manufactured with a great varie ...
attached to its gate, and if the output voltage of the supply rises above the Zener voltage, the thyristor will conduct and short-circuit the power supply output to ground (in general also tripping an upstream breaker or
fuse Fuse or FUSE may refer to: Devices * Fuse (electrical), a device used in electrical systems to protect against excessive current ** Fuse (automotive), a class of fuses for vehicles * Fuse (hydraulic), a device used in hydraulic systems to protect ...
). This kind of protection circuit is known as a
crowbar A crowbar, also called a wrecking bar, pry bar or prybar, pinch-bar, or occasionally a prise bar or prisebar, colloquially, in Britain and Australia sometimes called a jemmy or jimmy (also called jemmy bar), gooseneck, or pig foot, is a tool ...
, and has the advantage over a standard circuit breaker or fuse in that it creates a high-conductance path to ground for the damaging supply voltage and potentially for stored energy in the system being powered. The first large-scale application of thyristors, with associated triggering diac, in consumer products related to stabilized power supplies within color
television Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertisin ...
receivers in the early 1970s. The stabilized high voltage DC supply for the receiver was obtained by moving the switching point of the thyristor device up and down the falling slope of the positive going half of the AC supply input (if the rising slope was used the output voltage would always rise towards the peak input voltage when the device was triggered and thus defeat the aim of regulation). The precise switching point was determined by the load on the DC output supply, as well as AC input fluctuations. Thyristors have been used for decades as light dimmers in
television Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertisin ...
,
motion picture A film also called a movie, motion picture, moving picture, picture, photoplay or (slang) flick is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, feelings, beauty, or atmosphere ...
s, and
theater Theatre or theater is a collaborative form of performing art that uses live performers, usually actor, actors or actresses, to present the experience of a real or imagined event before a live audience in a specific place, often a stage. The p ...
, where they replaced inferior technologies such as
autotransformer An autotransformer is an electrical transformer with only one winding. The "auto" (Greek for "self") prefix refers to the single coil acting alone, not to any kind of automatic mechanism. In an autotransformer, portions of the same winding act as ...
s and
rheostat A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat. The measuring instrume ...
s. They have also been used in photography as a critical part of flashes (strobes).


Snubber circuits

Thyristors can be triggered by a high rise-rate of off-state voltage. Upon increasing the off-state voltage across the anode and cathode of the thyristor, there will be a flow of charges similar to the charging current of a capacitor. The maximum rate of rise of off-state voltage or dV/dt rating of a thyristor is an important parameter since it indicates the maximum rate of rise of anode voltage that does not bring thyristor into conduction when no gate signal is applied. When the flow of charges due to rate of rise of off-state voltage across the anode and cathode of the thyristor becomes equal to the flow of charges as injected when the gate is energized then it leads to random and false triggering of thyristor which is undesired. This is prevented by connecting a
resistor A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active el ...
-
capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...
(RC)
snubber A snubber is a device used to suppress ("snub") a phenomenon such as voltage transients in electrical systems, pressure transients in fluid systems (caused by for example water hammer) or excess force or rapid movement in mechanical systems. Ele ...
circuit between the anode and cathode in order to limit the dV/dt (i.e., rate of voltage change over time). Snubbers are energy-absorbing circuits used to suppress the voltage spikes caused by the circuit's inductance when a switch, electrical or mechanical, opens. The most common snubber circuit is a capacitor and resistor connected in series across the switch (transistor).


HVDC electricity transmission

Since modern thyristors can switch power on the scale of
megawatt The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units, International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), ...
s, thyristor valves have become the heart of
high-voltage direct current A high-voltage direct current (HVDC) electric power transmission system (also called a power superhighway or an electrical superhighway) uses direct current (DC) for electric power transmission, in contrast with the more common alternating curre ...
(HVDC) conversion either to or from alternating current. In the realm of this and other very high-power applications, both electrically triggered (ETT) and light-triggered (LTT) thyristors are still the primary choice. Thyristors are arranged into a
diode bridge A diode bridge is a bridge rectifier circuit of four diodes that is used in the process of converting alternating current (AC) from the input terminals to direct current (DC, i.e. fixed polarity) on the output terminals. Its function is to co ...
circuit and to reduce
harmonics A harmonic is a wave with a frequency that is a positive integer multiple of the ''fundamental frequency'', the frequency of the original periodic signal, such as a sinusoidal wave. The original signal is also called the ''1st harmonic'', the ...
are connected in series to form a 12-pulse converter. Each thyristor is cooled with
deionized water Purified water is water that has been mechanically filtered or processed to remove impurities and make it suitable for use. Distilled water was, formerly, the most common form of purified water, but, in recent years, water is more frequently puri ...
, and the entire arrangement becomes one of multiple identical modules forming a layer in a multilayer valve stack called a ''quadruple valve''. Three such stacks are typically mounted on the floor or hung from the ceiling of the
valve hall A valve hall is a building which contains the valves of the static inverters of a high-voltage direct current plant. The valves consist of thyristors, or at older plants, mercury arc rectifiers. Mercury arc rectifiers are usually supported by ...
of a long-distance transmission facility.


Comparisons to other devices


TRIAC

The functional drawback of a thyristor is that, like a diode, it only conducts in one direction so it can't be safely used with
AC current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in whic ...
. A similar self-latching 5-layer device, called a
TRIAC A TRIAC (triode for alternating current; also bidirectional triode thyristor or bilateral triode thyristor) is a three terminal electronic component that conducts current in either direction when triggered. The term TRIAC is a genericised tradem ...
, is able to work in both directions. This added capability, though, also can become a shortfall. Because the TRIAC can conduct in both directions,
reactive Reactive may refer to: *Generally, capable of having a reaction (disambiguation) *An adjective abbreviation denoting a bowling ball coverstock made of reactive resin *Reactivity (chemistry) *Reactive mind *Reactive programming See also *Reactanc ...
loads can cause it to fail to turn off during the zero-voltage instants of the AC power cycle. Because of this, use of TRIACs with (for example) heavily inductive motor loads usually requires the use of a "
snubber A snubber is a device used to suppress ("snub") a phenomenon such as voltage transients in electrical systems, pressure transients in fluid systems (caused by for example water hammer) or excess force or rapid movement in mechanical systems. Ele ...
" circuit around the TRIAC to assure that it will turn off with each half-cycle of mains power. Inverse parallel SCRs can also be used in place of the triac; because each SCR in the pair has an entire half-cycle of reverse polarity applied to it, the SCRs, unlike TRIACs, are sure to turn off. The "price" to be paid for this arrangement, however, is the added complexity of two separate, but essentially identical gating circuits.


Power MOSFETs and IGBTs

Although thyristors are heavily used in megawatt-scale
rectification Rectification has the following technical meanings: Mathematics * Rectification (geometry), truncating a polytope by marking the midpoints of all its edges, and cutting off its vertices at those points * Rectifiable curve, in mathematics * Recti ...
of AC to DC, in low- and medium-power (from few tens of watts to few tens of kilowatts) applications they have virtually been replaced by other devices with superior switching characteristics like
Power MOSFET A power MOSFET is a specific type of metal–oxide–semiconductor field-effect transistor (MOSFET) designed to handle significant power levels. Compared to the other power semiconductor devices, such as an insulated-gate bipolar transistor (IG ...
s or
IGBT An insulated-gate bipolar transistor (IGBT) is a three-terminal power semiconductor device primarily used as an electronic switch, which, as it was developed, came to combine high efficiency and fast switching. It consists of four alternating lay ...
s. One major problem associated with SCRs is that they are not fully controllable switches. The GTO thyristor and
IGCT The integrated gate-commutated thyristor (IGCT) is a power semiconductor electronic device, used for switching electric current in industrial equipment. It is related to the gate turn-off (GTO) thyristor. It was jointly developed by Mitsubish ...
are two devices related to the thyristor that address this problem. In high-frequency applications, thyristors are poor candidates due to long switching times arising from bipolar conduction. MOSFETs, on the other hand, have much faster switching capability because of their unipolar conduction (only
majority carriers In physics, a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and electron hole, holes. Th ...
carry the current).


Failure modes

Thyristor manufacturers generally specify a region of safe firing defining acceptable levels of voltage and current for a given
operating temperature An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
. The boundary of this region is partly determined by the requirement that the maximum permissible gate power (PG), specified for a given trigger pulse duration, is not exceeded. As well as the usual failure modes due to exceeding voltage, current or power ratings, thyristors have their own particular modes of failure, including: * Turn on di/dt – in which the rate of rise of on-state current after triggering is higher than can be supported by the spreading speed of the active conduction area (SCRs & triacs). * Forced commutation – in which the transient peak reverse recovery current causes such a high voltage drop in the sub-cathode region that it exceeds the reverse breakdown voltage of the gate cathode diode junction (SCRs only). * Switch on dv/dt – the thyristor can be spuriously fired without trigger from the gate if the anode-to-cathode voltage rise-rate is too great.


Silicon carbide thyristors

In recent years, some manufacturers have developed thyristors using
silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal sin ...
(SiC) as the semiconductor material. These have applications in high temperature environments, being capable of operating at temperatures up to 350 °C.


Types

* ACS * ACST * AGT – Anode Gate Thyristor – A thyristor with gate on n-type layer near to the anode * ASCR – Asymmetrical SCR * BCT – Bidirectional Control Thyristor – A bidirectional switching device containing two thyristor structures with separate gate contacts * BOD – Breakover
Diode A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diode ...
– A gateless thyristor triggered by avalanche current ** DIAC – Bidirectional trigger device ** Dynistor – Unidirectional switching device **
Shockley diode The Shockley diode (named after physicist William Shockley) is a four-layer semiconductor diode, which were one of the first semiconductor devices invented. It is a PNPN diode, with alternating layers of P-type and N-type material. It is equ ...
– Unidirectional trigger and switching device ** SIDAC – Bidirectional switching device **
Trisil Trisil is a trade name for a thyristor surge protection device, an electronic component designed to protect electronic circuits against overvoltage. Unlike a transient voltage suppression diodes, such as Transil, a Trisil acts as a crowbar devic ...
, SIDACtor – Bidirectional protection devices * BRT – Base Resistance Controlled Thyristor *
ETO ETO may refer to: Science and technology * Emitter turn off thyristor, a semiconductor device * Ethylene oxide, an organic compound * RUNX1T1, a gene * Efforts to Outcomes, software produced by Social Solutions Sports * ETO-SZESE Győr FKC, a H ...
– Emitter Turn-Off ThyristorRashid, Muhammad H.(2011); ''Power Electronics (3rd ed.)''. Pearson, * GTO – Gate Turn-Off thyristor ** DB-GTO – Distributed buffer gate turn-off thyristor ** MA-GTO – Modified anode gate turn-off thyristor *
IGCT The integrated gate-commutated thyristor (IGCT) is a power semiconductor electronic device, used for switching electric current in industrial equipment. It is related to the gate turn-off (GTO) thyristor. It was jointly developed by Mitsubish ...
– Integrated gate-commutated thyristor * Ignitor – Spark generators for fire-lighter ckts * LASCR – Light-activated SCR, or LTT – light-triggered thyristor * LASS – light-activated semiconducting switch * MCT – MOSFET Controlled Thyristor – It contains two additional
FET The field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor. FETs (JFETs or MOSFETs) are devices with three terminals: ''source'', ''gate'', and ''drain''. FETs contr ...
structures for on/off control. * CSMT or MCS – MOS composite static induction thyristor * PUT or PUJT – Programmable Unijunction Transistor – A thyristor with gate on n-type layer near to the anode used as a functional replacement for
unijunction transistor A unijunction transistor (UJT) is a three-lead electronic semiconductor device with only one junction that acts exclusively as an electrically controlled switch. The UJT is not used as a linear amplifier. It is used in free-running oscillators, sy ...
* RCT – Reverse Conducting Thyristor * SCS – Silicon Controlled Switch or Thyristor Tetrode – A thyristor with both cathode and anode gates * SCR – Silicon Controlled Rectifier * SITh – Static Induction Thyristor, or FCTh – Field Controlled Thyristor – containing a gate structure that can shut down anode current flow. *
TRIAC A TRIAC (triode for alternating current; also bidirectional triode thyristor or bilateral triode thyristor) is a three terminal electronic component that conducts current in either direction when triggered. The term TRIAC is a genericised tradem ...
– Triode for Alternating Current – A bidirectional switching device containing two thyristor structures with common gate contact *
Quadrac {{no footnotes, date=September 2013 A QUADRAC is a special type of ''thyristor'' which combines a DIAC and a TRIAC in a single package. The DIAC is the triggering device for the TRIAC. Thyristors are four-layer (PNPN) semiconductor devices that ac ...
– special type of thyristor which combines a DIAC and a
TRIAC A TRIAC (triode for alternating current; also bidirectional triode thyristor or bilateral triode thyristor) is a three terminal electronic component that conducts current in either direction when triggered. The term TRIAC is a genericised tradem ...
into a single package.


Reverse conducting thyristor

A reverse conducting thyristor (RCT) has an integrated reverse
diode A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diode ...
, so is not capable of reverse blocking. These devices are advantageous where a reverse or freewheel diode must be used. Because the SCR and
diode A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diode ...
never conduct at the same time they do not produce heat simultaneously and can easily be integrated and cooled together. Reverse conducting thyristors are often used in
frequency changer A frequency changer or frequency converter is an electronic or electromechanical device that converts alternating current ( AC) of one frequency to alternating current of another frequency. The device may also change the voltage, but if it does, ...
s and
inverters A power inverter, inverter or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the opp ...
.


Photothyristors

Photothyristors are activated by light. The advantage of photothyristors is their insensitivity to electrical signals, which can cause faulty operation in electrically noisy environments. A light-triggered thyristor (LTT) has an optically sensitive region in its gate, into which
electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic field, electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, inf ...
(usually
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
) is coupled by an
optical fiber An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means to ...
. Since no electronic boards need to be provided at the potential of the thyristor in order to trigger it, light-triggered thyristors can be an advantage in high-voltage applications such as
HVDC A high-voltage direct current (HVDC) electric power transmission system (also called a power superhighway or an electrical superhighway) uses direct current (DC) for electric power transmission, in contrast with the more common alternating curren ...
. Light-triggered thyristors are available with in-built over-voltage (VBO) protection, which triggers the thyristor when the forward voltage across it becomes too high; they have also been made with in-built ''forward recovery protection'', but not commercially. Despite the simplification they can bring to the electronics of an HVDC valve, light-triggered thyristors may still require some simple monitoring electronics and are only available from a few manufacturers. Two common photothyristors include the light-activated SCR (LASCR) and the light-activated
TRIAC A TRIAC (triode for alternating current; also bidirectional triode thyristor or bilateral triode thyristor) is a three terminal electronic component that conducts current in either direction when triggered. The term TRIAC is a genericised tradem ...
. A LASCR acts as a switch that turns on when exposed to light. Following light exposure, when light is absent, if the power is not removed and the polarities of the cathode and anode have not yet reversed, the LASCR is still in the "on" state. A light-activated TRIAC resembles a LASCR, except that it is designed for alternating currents.


See also

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Thyristor-controlled reactor In an electric power transmission system, a thyristor-controlled reactor (TCR) is a reactance connected in series with a bidirectional thyristor valve. The thyristor valve is phase-controlled, which allows the value of delivered reactive power t ...
*
Insulated-gate bipolar transistor An insulated-gate bipolar transistor (IGBT) is a three-terminal power semiconductor device primarily used as an electronic switch, which, as it was developed, came to combine high efficiency and fast switching. It consists of four alternating lay ...
*
Latch-up A latch-up is a type of short circuit which can occur in an integrated circuit (IC). More specifically it is the inadvertent creation of a low- impedance path between the power supply rails of a MOSFET circuit, triggering a parasitic structure whi ...
*
Quadrac {{no footnotes, date=September 2013 A QUADRAC is a special type of ''thyristor'' which combines a DIAC and a TRIAC in a single package. The DIAC is the triggering device for the TRIAC. Thyristors are four-layer (PNPN) semiconductor devices that ac ...
*
Thyratron A thyratron is a type of gas-filled tube used as a high-power electrical switch and controlled rectifier. Thyratrons can handle much greater currents than similar hard-vacuum tubes. Electron multiplication occurs when the gas becomes ionized, pro ...
*
Thyristor drive Motor drive means a system that includes a motor. An adjustable speed motor drive means a system that includes a motor that has multiple operating speeds. A variable speed motor drive is a system that includes a motor and is continuously variabl ...


References


Sources

* * ''Thyristor Theory and Design Considerations''; ON Semiconductor; 240 pages; 2006; HBD855/D. (Free PDF download)
/small> * Ulrich Nicolai, Tobias Reimann, Jürgen Petzoldt, Josef Lutz: ''Application Manual IGBT and MOSFET Power Modules'', 1. Edition, ISLE Verlag, 1998, .
/small> * ''SCR Manual''; 6th edition; General Electric Corporation; Prentice-Hall; 1979.


External links



– by Frank William Gutzwiller (of G.E.)

– from All About Circuits






Thyristor basics
{{Authority control Electric power systems components High-voltage direct current Power electronics Solid state switches