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Encyclopedia > Thyristor
Circuit symbol for a thyristor
Circuit symbol for a thyristor

The thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as a switch, conducting when their gate receives a current pulse, and continue to conduct for as long as they are forward biased. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... ... Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials, principally silicon, germanium, and gallium arsenide. ... An N-type semiconductor is obtained by carrying out a process of doping, that is adding a certain type of atoms to the semiconductor in order to increase the number of free (in this case negative) charge carriers. ... A P-type semiconductor is obtained by carrying out a process of doping, that is adding a certain type of atoms to the semiconductor in order to increase the number of free (in this case positive) charges. ...


Some sources define silicon controlled rectifiers and thyristors as synonymous[1]; others define SCRs as a subset of thyristors, along with gate turn-off thyristor (GTO), triode ac switch (triac), static induction transistor (SIT), static induction thyristor (SITH) and MOS-controlled thyristor (MCT). Among the latter, the International Electrotechnical Commission 60747-6 standard stands out. A Silicon Controlled Rectifier (or semiconductor controlled rectifier) is a 4-layer solid state device that controls current flow. ... The International Electrotechnical Commission (IEC) is an international standards organization dealing with electrical, electronic and related technologies. ...


Non-SCR thyristors include devices with more than four layers, such as triacs and DB-GTOs[2]. Triac Schematic Symbol A TRIAC, or TRIode for Alternating Current is an electronic component approximately equivalent to two silicon-controlled rectifiers (SCRs/thyristors) joined in inverse parallel (paralleled but with the polarity reversed) and with their gates connected together. ... A distributed buffer gate turn-off thyristor (DB-GTO) is a thyristor with additional pn layers in the drift region to reshape the field profile and increase the voltage blocked in the off state. ...

Contents

Function

image:thyristor.svg

The thyristor is a four-layer semiconducting device, with each layer consisting of an alternately N-type or P-type material, for example P-N-P-N. The main terminals, labeled anode and cathode, are across the full four layers, and the control terminal, called the gate, is attached to p-type material near to the cathode. (A variant called a 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 Transistors, arranged to cause the self-latching action. Image File history File links No higher resolution available. ... An N-type semiconductor is obtained by carrying out a process of doping, that is adding a certain type of atoms to the semiconductor in order to increase the number of free (in this case negative) charge carriers. ... A P-type semiconductor is obtained by carrying out a process of doping, that is adding a certain type of atoms to the semiconductor in order to increase the number of free (in this case positive) charges. ... A bipolar junction transistor (BJT) is a type of transistor. ...


Thyristors have three states:

  1. Reverse blocking mode -- Voltage is applied in the direction that would be blocked by a diode
  2. Forward blocking mode -- Voltage is applied in the direction that would cause a diode to conduct, but the thyristor has not yet been triggered into conduction
  3. 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). A p-n junction is formed by combining N-type and P-type semiconductors together in very close contact. ...

Layer Diagram of Thyristor
Layer Diagram of Thyristor

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 VAK is increased beyond the breakdown voltage VBO of the thyristor, avalanche breakdown of J2 takes place and the thyristor starts conducting (On state). Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Avalanche breakdown is a phenomenon that can occur in both insulating and semiconducting materials. ...


If a positive potential VG is applied at the gate terminal with respect to the cathode, the breakdown of the junction J2 occurs at a lower value of VAK. By selecting an appropriate value of VG, the thyristor can be switched into the on state immediately.


It should be noted that once avalanche breakdown has occurred, the thyristor continues to conduct, irrespective of the gate voltage, until either: (a) the potential VG is removed or (b) the current through the device (anode−cathode) is less than the holding current specified by the manufacturer. Hence VG can be a voltage pulse, such as the voltage output from a UJT relaxation oscillator. A Unijunction transistor (UJT) is an electronic semiconductor device. ... A relaxation oscillator is an oscillator in which a capacitor is charged gradually and then discharged rapidly. ...


These gate pulses are characterized in terms of gate trigger voltage (VGT) and gate trigger current (IGT). Gate trigger current varies inversely with gate pulse width in such a way that it is evident that there is a minimum gate charge required to trigger the thyristor. Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ...


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 conduct), providing the anode current has exceeded the latching current (IL). As long as the anode remains positively biased, it cannot be switched off until the anode current falls below the holding current (IH).

V - I Characteristics
V - I Characteristics

A thyristor can be switched off if the external circuit causes the anode to become negatively biased. In some applications this is done by switching a second thyristor to discharge a capacitor into the cathode of the first thyristor. This method is called forced commutation. Image File history File links Thyristor_char. ... Image File history File links Thyristor_char. ...


After a thyristor has been switched off by forced commutation, a finite time delay must have elapsed before the anode can be positively biased in the off-state. This minimum delay is called the circuit commutated turn off time (tQ). Attempting to positively bias the anode within this time causes the thyristor to be self-triggered by the remaining charge carriers (holes and electrons) that have not yet recombined. For the following two reasons the electron hole was introduced into calculations: If an electron is excited into higher state it leaves a hole in its old state. ... For other uses, see Electron (disambiguation). ... In the solid state physics of semiconductors, carrier generation and recombination are processes by which mobile electrons and electron holes are created and eliminated. ...


For applications with frequencies higher than the domestic AC mains supply (e.g. 50Hz or 60Hz), thyristors with lower values of tQ are required. Such fast thyristors are made by diffusing into the silicon heavy metals ions such as gold or platinum which act as charge combination centres. Alternatively, fast thyristors may be made by neutron irradiation of the silicon. A heavy metal is any of a number of higher atomic weight elements, which has the properties of a metallic substance at room temperature. ... This article is about the electrically charged particle. ... GOLD refers to one of the following: GOLD (IEEE) is an IEEE program designed to garner more student members at the university level (Graduates of the Last Decade). ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Standard atomic weight 195. ... This article or section does not adequately cite its references or sources. ... Irradiation is the process by which an item is exposed to radiation. ...


History

1956 The Silicon Controlled Rectifier (SCR) or Thyristor proposed by William Shockley in 1950 and championed by Moll and others at Bell Labs was developed first by power engineers at General Electric (G.E.) led by Gordon Hall and commercialised by G.E.'s Frank W. "Bill" Gutzwiller. Year 1956 (MCMLVI) was a leap year starting on Sunday (link will display full calendar) of the Gregorian calendar. ... William Bradford Shockley (February 13, 1910 – August 12, 1989) was a British-born American physicist and inventor. ... Year 1950 (MCML) was a common year starting on Sunday (link will display the full calendar) of the Gregorian calendar. ... Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) was the main research and development arm of the United States Bell System. ... “GE” redirects here. ...


Applications

A bank of six, 2000 A Thyristors (white pucks). The clear tubes are for cooling water
Thyristor voltage regulated by phase control

Thyristors are mainly used where high currents and voltages are involved, and are often used to control alternating currents, where the change of polarity of the current causes the device to automatically switch off; referred to as Zero Cross operation. The device can be said to operate synchronously as, once the device is open, it conducts current in phase with the voltage applied over its cathode to anode junction with no further gate modulation being required to replicate; the device is biased fully on. This is not to be confused with symmetrical operation, as the output is unidirectional, flowing only from cathode to anode, and so is asymmetrical in nature. A module containing thyristors for the Nelson River Bipole. ... A module containing thyristors for the Nelson River Bipole. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... City lights viewed in a motion blurred exposure. ... A zero cross circuit is an electrical circuit that starts operation with the AC load voltage at close to zero-phase. ...


Thyristors can be used as the control elements for phase angle triggered controllers, also known as phase fired controllers. To meet Wikipedias quality standards, this article or section may require cleanup. ...


Thyristors can also be found in power supplies for digital circuits, where they can be used as a sort of "circuit breaker" or "crowbar" to prevent a failure in the power supply from damaging downstream components. The thyristor is used in conjunction with a zener diode attached to its gate, and when the output voltage of the supply rises above the zener voltage, the thyristor conducts, shorting the power supply output to ground (and in general blowing an upstream fuse). This Article does not cite any references or sources. ... A 2 pole miniature circuit breaker A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. ... Zener diode schematic symbol A Zener diode is a type of diode that permits current to flow in the forward direction like a normal diode, but also in the reverse direction if the voltage is larger (not equal to, but larger) than the rated breakdown voltage known as Zener knee... Look up fuse in Wiktionary, the free dictionary. ...


The first large scale application of thyristors, with associated triggering diac, in consumer products related to stabilized power supplies within color television receivers in the early 1970s. The stabilized high voltage d.c 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 a.c 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 output d.c. supply as well fluctuations on the input a.c. supply. They proved to be unpopular with the a.c. grid power supplier companies because the simultaneous switching of many television receivers, all at approximately the same time, introduced asymmetry into the supply waveform and, as a consequence injected d.c. back into the grid with a tendency towards saturation of transformer cores and overheating. Thyristors were largely phased out in this kind of application by the end of the decade. DIAC For other uses, see DIAC (disambiguation). ... The 1970s decade refers to the years from 1970 to 1979, also called The Seventies. ... Power line redirects here. ...


Snubber circuits

Because thyristors can be triggered on by a high rate of rise of off-state voltage, in many applications this is prevented by connecting a resistor-capacitor (RC) snubber circuit between the anode and cathode terminals in order to limit the dV/dt (i.e., rate of change of voltage versus time). Resistor symbols (non-European) Resistor symbols (Europe, IEC) Axial-lead resistors on tape. ... See Capacitor (component) for a discussion of specific types. ... A snubber is a simple electrical circuit used to suppress (snub) electrical transients. ...


Comparisons to other devices

SCR rated about 100 amperes, 1200 volts
SCR rated about 100 amperes, 1200 volts

The functional drawback of a thyristor is that, like a diode, it only conducts in one direction. A similar self-latching 5-layer device, called a TRIAC, 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 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" 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. Image File history File links Download high resolution version (589x702, 42 KB) Summary SCR, rated about 100 amperes, 1200 volts, 1/2 inch stud, photographed by C J Cowie Licensing I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the... Image File history File links Download high resolution version (589x702, 42 KB) Summary SCR, rated about 100 amperes, 1200 volts, 1/2 inch stud, photographed by C J Cowie Licensing I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the... Triac Schematic Symbol A TRIAC, or TRIode for Alternating Current is an electronic component approximately equivalent to two silicon-controlled rectifiers (SCRs/thyristors) joined in inverse parallel (paralleled but with the polarity reversed) and with their gates connected together. ... It has been suggested that Electric reactance be merged into this article or section. ... City lights viewed in a motion blurred exposure. ... An electric current i flowing around a circuit produces a magnetic field and hence a magnetic flux Φ through the circuit. ... A snubber is a simple electrical circuit used to suppress (snub) electrical transients. ... Two antiparallel molecules run side-by-side in opposite directions. ...


An earlier gas filled tube device called a Thyratron 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" that the term "thyristor" is derived. Gas filled tubes are arrangements of electrodes in a gas within an insulating, temperature-resistant envelope. ... A thyratron is a type of gas filled tube used as a high energy electrical switch. ... For other uses, see Transistor (disambiguation). ...


Modern thyristors can switch large amounts of power (up to megawatts). In the realm of very high power applications, they are still the primary choice. However, in low and medium power (from few tens of watts to few tens of kilowatts) they have almost been replaced by other devices with superior switching characteristics like MOSFETs or IGBTs. One major problem associated with SCRs is that they are not fully controllable switches. The GTO (Gate Turn-off Thyristor) and IGCT are two related devices which address this problem. In high-frequency applications, thyristors are poor candidates due to large switching times arising from bipolar conduction. MOSFETs, on the other hand, have much faster switching capability because of their unipolar conduction (only majority carriers carry the current). HVDC or high-voltage, direct current electric power transmission systems contrast with the more common alternating-current systems as a means for the bulk transmission of electrical power. ... Two power MOSFETs in the surface-mount package D2PAK. Each of these component can sustain a blocking voltage of 30 volts and a continuous current of 120 amperes. ... The Insulated Gate Bipolar Transistor combines the simple gate drive characteristics of the MOSFET with the high current and low saturation voltage capability of bipolar transistors by combining an isolated gate FET for the control input, and a bipolar power transistor as a switch, in a single device. ... A Gate turn-off thyristor (GTO) is a special type of thyristor, a high-power semiconductor device. ... Integrated Gate Commutated Thyristor (IGCT) can be turned on and off by the gate signal, has low conduction loss and requires no dv/dt snubber. ... Majority carrier denotes the carrier which is primarily responsible for current transport in a piece of semiconductor. ...


Failure modes

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).

Silicon carbide thyristors

In recent years, some manufacturers[3] have developed thyristors using Silicon carbide (SiC) as the semiconductor material. These have applications in high temperature environments, being capable of operating at temperatures up to 350 °C. Except where noted otherwise, data are given for materials in their standard state (at 25 Â°C, 100 kPa) Infobox disclaimer and references Silicon carbide (SiC) is a ceramic compound of silicon and carbon that is manufactured on a large scale for use mainly as an abrasive but also occurs in...


Types of thyristors

  • SCR — Silicon controlled rectifier
  • ASCR — asymmetrical SCR
  • RCT — reverse conducting thyristor
  • LASCR — light activated SCR, or LTT — light triggered thyristor
  • DIAC & SIDAC — both forms of trigger devices
  • BOD — breakover diode — a gateless thyristor triggered by avalanche current, used in protection applications
  • TRIAC — a bidirectional switching device containing two thyristor structures
  • GTO — gate turn-off thyristor
  • IGCT — Integrated gate commutated thyristor
    • MA-GTO — Modified anode gate turn-off thyristor
    • DB-GTO — Distributed buffer gate turn-off thyristor
  • MCT — MOSFET controlled thyristor containing two additional FET structures for on/off control.
    • BRT — Base Resistance Controlled Thyristor
  • SITh — Static induction thyristor, or FCTh — Field controlled thyristor containing a gate structure that can shut down anode current flow.

The GTO is a tri state device. with a 8 function setup. it also has a equation: v=j-o x n/n o A Silicon Controlled Rectifier (or semiconductor controlled rectifier) is a 4-layer solid state device that controls current flow. ... Reverse conducting thyristor (RCT) is high-power switching semiconductor device similar to thyristor with integrated reverse diode. ... LTT is an initialism for the following: Leninist-Trotskyist Tendency Lancastrian Transport Trust a charity concerned with preserving trams and buses of the Fylde Coast in the North West of England Libya Telecom & Technology Linux Trace Toolkit Local Transport Today a UK publication for the transport planning profession This page... DIAC For other uses, see DIAC (disambiguation). ... SIDAC The SIDAC, or SIlicon Diode for Alternating Current, is a semiconductor of the thyristor family. ... An avalanche diode is a diode (usually made from silicon, but can be made from another semiconductor) that is designed to break down and conduct at a specified reverse bias voltage. ... Triac Schematic Symbol A TRIAC, or TRIode for Alternating Current is an electronic component approximately equivalent to two silicon-controlled rectifiers (SCRs/thyristors) joined in inverse parallel (paralleled but with the polarity reversed) and with their gates connected together. ... A Gate turn-off thyristor (GTO) is a special type of thyristor, a high-power semiconductor device. ... Integrated Gate Commutated Thyristor (IGCT) can be turned on and off by the gate signal, has low conduction loss and requires no dv/dt snubber. ... A distributed buffer gate turn-off thyristor (DB-GTO) is a thyristor with additional pn layers in the drift region to reshape the field profile and increase the voltage blocked in the off state. ... MOS Controlled Thyristor (or MCT) is voltage controlled fully controllable thyristor. ... Large power N-channel field effect transistor The field-effect transistor (FET) is a transistor that relies on an electric field to control the shape and hence the conductivity of a channel in a semiconductor material. ... BRT may mean: Be right there in Internet slang. ... The SI-thyristors have a buried gate structure in which the gate electrodes are placed in n-base region. ...


References

Footnotes

  1. ^ Christiansen, Donald; Alexander, Charles K. (2005); Standard Handbook of Electrical Engineering (5th ed.). McGraw-Hill, ISBN 0-07-138421-9
  2. ^ Dorf, Richard C., editor (1997), Electrical Engineering Handbook (2nd ed.). CRC Press, IEEE Press, Ron Powers Publisher, ISBN 0-8493-8574-1
  3. ^ Example: Silicon Carbide Inverter Demonstrates Higher Power Output in Power Electronics Technology (2006-02-01)

Bibliography

  • General Electric Corporation, SCR Manual, 6th edition, Prentice-Hall, 1979.

External links

Look up Thyristor in
Wiktionary, the free dictionary.
  • The Early History of the Silicon Controlled Rectifier — by Frank William Gutzwiller (of G.E.)

Wikipedia does not have an article with this exact name. ... Wiktionary (a portmanteau of wiki and dictionary) is a multilingual, Web-based project to create a free content dictionary, available in over 150 languages. ...

See also


 
 

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