Thyristor
Encyclopedia
A thyristor is a solid-state
semiconductor device
with four layers of alternating N
and P-type
material. They act as bistable switches, conducting when their gate receives a current trigger, and continue to conduct while they are forward biased (that is, while the voltage across the device is not reversed).
Some sources define silicon controlled rectifiers and thyristors as synonymous.
Other sources define thyristors as a larger set of devices with at least four layers of alternating N and P-type material, including:
or P-type
material, for example P-N-P-N. The main terminals, labelled 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 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
s, arranged to cause the self-latching action:
Thyristors have three states:
s (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 VAK is increased beyond the breakdown voltage VBO of the thyristor, avalanche breakdown
of J2 takes place and the thyristor starts conducting (On state).
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 suddenly.
Once avalanche breakdown has occurred, the thyristor continues to conduct, irrespective of the gate voltage, until: (a) the potential VAK 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
.
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.
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.
After a thyristor has been switched off by forced commutation, a finite time delay must have elapsed before the anode can again be positively biased and retain the thyristor 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 electron
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 tQ are required. Such fast thyristors are made by diffusing into the silicon heavy metals
ion
s such as gold
or platinum
which act as charge combination centres. Alternatively, fast thyristors may be made by neutron
irradiation
of the silicon.
in 1950 and championed by Moll and others at Bell Labs
was developed in 1956 by power engineers at General Electric
(G.E.) led by Gordon Hall and commercialized by G.E.'s Frank W. "Bill" Gutzwiller.
Thyristors are mainly used where high currents and voltages are involved, and are often used to control alternating current
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 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.
Thyristors can be used as the control elements for phase angle triggered controllers, also known as phase fired controllers
.
They can also be found in power supplies for digital circuits, where they are used as a sort of "circuit breaker
" or "crowbar" to prevent a failure in the power supply from damaging downstream components. A 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 will conduct, then short-circuit the power supply output to ground (and in general blowing an upstream fuse
).
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 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 output DC supply as well fluctuations on the input AC supply.
Thyristors have been used for decades as lighting dimmers
in television
, motion pictures, and theater, where they replaced inferior technologies such as autotransformer
s and rheostats. They have also been used in photography as a critical part of flashes (strobes).
-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).
Since modern thyristors can switch power on the scale of megawatts, thyristor valves have become the heart of high-voltage direct current
(HVDC) conversion either to or from alternating current. In the realm of this and other very high power applications, both electronically switched (ETT) and light switched (LTT) thyristors are still the primary choice. The valves are arranged in stacks usually suspended from the ceiling of a transmission building called a valve hall. Thyristors are arranged into a Graetz bridge circuit and to avoid harmonics are connected in series to form a 12 pulse converter. Each thyristor is cooled with deionized water, 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 hung from the ceiling of the valve building of a long distance transmission facility.
, 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.
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.
Although thyristors are heavily used in megawatt scale rectification
of AC to DC, 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).
(SiC) as the semiconductor material. These have applications in high temperature environments, being capable of operating at temperatures
up to 350 °C.
, 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
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
s and inverters
.
Solid state (electronics)
Solid-state electronics are those circuits or devices built entirely from solid materials and in which the electrons, or other charge carriers, are confined entirely within the solid material...
semiconductor device
Semiconductor device
Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials, principally silicon, germanium, and gallium arsenide, as well as organic semiconductors. Semiconductor devices have replaced thermionic devices in most applications...
with four layers of alternating N
N-type semiconductor
N-type semiconductors are a type of extrinsic semiconductor where the dopant atoms are capable of providing extra conduction electrons to the host material . This creates an excess of negative electron charge carriers....
and P-type
P-type semiconductor
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 charge carriers ....
material. They act as bistable switches, conducting when their gate receives a current trigger, and continue to conduct while they are forward biased (that is, while the voltage across the device is not reversed).
Some sources define silicon controlled rectifiers and thyristors as synonymous.
Other sources define thyristors as a larger set of devices with at least four layers of alternating N and P-type material, including:
- Distributed Buffer - Gate Turn-off Thyristor (DB-GTO)
- Gate turn-off thyristorGate turn-off thyristorA gate turn-off thyristor is a special type of thyristor, a high-power semiconductor device. GTOs, as opposed to normal thyristors, are fully controllable switches which can be turned on and off by their third lead, the GATE lead.-Device description:...
(GTO) - Integrated gate commutated thyristorIGCTThe Integrated Gate-Commutated Thyristor is a power semiconductor electronic device, used for switching electric current in industrial equipment. It is related to the gate turn-off thyristor. Like the GTO thyristor, the IGCT is a fully controllable power switch, meaning that it can be turned...
(IGCT) - MOS composite static induction thyristor/CSMTMOS composite static induction thyristor/CSMTMOS composite static induction thyristor is a combination of a MOS transistor connected in cascode relation to the SI-thyristor....
- MOS Controlled ThyristorMOS Controlled ThyristorMOS Controlled Thyristor is voltage controlled fully controllable thyristor. The MCT is similar in operation with GTO thyristor, but it has voltage controlled insulated gate. It has two MOSFETs in its equivalent circuit. One is responsible for turn-on and the another is responsible for turn-off...
(MCT) - Reverse conducting thyristor
- Silicon controlled rectifier (SCR)
- Static induction thyristor (SITh)
- Triode AC switchTRIACTRIAC, from Triode for Alternating Current, is a genericized tradename for an electronic component that can conduct current in either direction when it is triggered , and is formally called a bidirectional triode thyristor or bilateral triode thyristor.TRIACs belong to the thyristor family and are...
(TRIAC)
Function
The thyristor is a four-layer, three terminal semiconducting device, with each layer consisting of alternately N-typeN-type semiconductor
N-type semiconductors are a type of extrinsic semiconductor where the dopant atoms are capable of providing extra conduction electrons to the host material . This creates an excess of negative electron charge carriers....
or P-type
P-type semiconductor
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 charge carriers ....
material, for example P-N-P-N. The main terminals, labelled 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 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
Bipolar junction transistor
|- align = "center"| || PNP|- align = "center"| || NPNA bipolar transistor is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications. Bipolar transistors are so named because their operation involves both electrons...
s, arranged to cause the 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 yet 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 junctionP-n junction
A p–n junction is formed at the boundary between a P-type and N-type semiconductor created in a single crystal of semiconductor by doping, for example by ion implantation, diffusion of dopants, or by epitaxy .If two separate pieces of material were used, this would...
s (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 VAK is increased beyond the breakdown voltage VBO of the thyristor, avalanche breakdown
Avalanche breakdown
Avalanche breakdown 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 insulators. It is a type of electron avalanche...
of J2 takes place and the thyristor starts conducting (On state).
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 suddenly.
Once avalanche breakdown has occurred, the thyristor continues to conduct, irrespective of the gate voltage, until: (a) the potential VAK 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
Relaxation oscillator
A relaxation oscillator is an oscillator based upon the behavior of a physical system's return to equilibrium after being disturbed. That is, a dynamical system within the oscillator continuously dissipates its internal energy...
.
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
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
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 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).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.
After a thyristor has been switched off by forced commutation, a finite time delay must have elapsed before the anode can again be positively biased and retain the thyristor 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
Electron hole
An electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics, chemistry, and electrical engineering. The concept describes the lack of an electron at a position where one could exist in an atom or atomic lattice...
and electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s) that have not yet recombined
Carrier generation and recombination
In the solid state physics of semiconductors, carrier generation and recombination are processes by which mobile charge carriers are created and eliminated. Carrier generation and recombination processes are fundamental to the operation of many optoelectronic semiconductor devices, such as...
.
For applications with frequencies higher than the domestic AC mains supply (e.g. 50 Hz or 60 Hz), thyristors with lower values of tQ are required. Such fast thyristors are made by diffusing into the silicon heavy metals
Heavy metals
A heavy metal is a member of a loosely-defined subset of elements that exhibit metallic properties. It mainly includes the transition metals, some metalloids, lanthanides, and actinides. Many different definitions have been proposed—some based on density, some on atomic number or atomic weight,...
ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s such as gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
or platinum
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
which act as charge combination centres. Alternatively, fast thyristors may be made by neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
irradiation
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 a specific purpose, rather than radiation exposure to...
of the silicon.
History
The Silicon Controlled Rectifier (SCR) or Thyristor proposed by William ShockleyWilliam Shockley
William Bradford Shockley Jr. was an American physicist and inventor. Along with John Bardeen and Walter Houser Brattain, Shockley co-invented the transistor, for which all three were awarded the 1956 Nobel Prize in Physics.Shockley's attempts to commercialize a new transistor design in the 1950s...
in 1950 and championed by Moll and others at Bell Labs
Bell Labs
Bell Laboratories is the research and development subsidiary of the French-owned Alcatel-Lucent and previously of the American Telephone & Telegraph Company , half-owned through its Western Electric manufacturing subsidiary.Bell Laboratories operates its...
was developed in 1956 by power engineers at General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
(G.E.) led by Gordon Hall and commercialized by G.E.'s Frank W. "Bill" Gutzwiller.
Applications
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
s, where the change of polarity of the current causes the device to switch off automatically; referred to as Zero Cross
Zero cross circuit
A zero cross circuit is an electrical circuit that starts operation with the AC load voltage at close to zero-phase. This is in relation to solid state relays, such as triacs and silicon controlled rectifiers...
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.
Thyristors can be used as the control elements for phase angle triggered controllers, also known as phase fired controllers
Phase fired controllers
Phase control , also called phase cutting, is a method of pulse width modulation for power limiting, applied to AC voltages...
.
They can also be found in power supplies for digital circuits, where they are used as a sort of "circuit breaker
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. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...
" or "crowbar" to prevent a failure in the power supply from damaging downstream components. A thyristor is used in conjunction with a Zener diode
Zener diode
A Zener diode is a special kind of diode which allows current to flow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, "Zener knee voltage" or "Zener...
attached to its gate, and when the output voltage of the supply rises above the Zener voltage, the thyristor will conduct, then short-circuit the power supply output to ground (and in general blowing an upstream fuse
Fuse (electrical)
In electronics and electrical engineering, a fuse is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit...
).
The first large scale application of thyristors, with associated triggering diac
DIAC
The DIAC, or 'diode for alternating current', is a diode that conducts current only after its breakover voltage has been reached momentarily....
, in consumer products related to stabilized power supplies within color television
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
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 output DC supply as well fluctuations on the input AC supply.
Thyristors have been used for decades as lighting dimmers
Dimmer
Dimmers are devices used to vary the brightness of a light. By decreasing or increasing the RMS voltage and, hence, the mean power to the lamp, it is possible to vary the intensity of the light output...
in television
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
, motion pictures, and theater, where they replaced inferior technologies such as autotransformer
Autotransformer
An autotransformer is an electrical transformer with only one winding. The auto prefix refers to the single coil acting on itself rather than any automatic mechanism. In an autotransformer portions of the same winding act as both the primary and secondary. The winding has at least three taps where...
s and rheostats. They have also been used in photography as a critical part of flashes (strobes).
Snubber circuits
Thyristors can be triggered by a high rate of rise of off-state voltage. This is prevented by connecting a resistorResistor
A linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element.The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's...
-capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
(RC) snubber circuit
Snubber
A snubber is a device used to suppress voltage transients in electrical systems, pressure transients in fluid systems, or excess force or rapid movement in mechanical systems.-Electrical systems:...
between the anode and cathode terminals in order to limit the dV/dt (i.e., rate of change of voltage versus time).
HVDC electricity transmission
High-voltage direct current
A high-voltage, direct current electric power transmission system uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses...
(HVDC) conversion either to or from alternating current. In the realm of this and other very high power applications, both electronically switched (ETT) and light switched (LTT) thyristors are still the primary choice. The valves are arranged in stacks usually suspended from the ceiling of a transmission building called a valve hall. Thyristors are arranged into a Graetz bridge circuit and to avoid harmonics are connected in series to form a 12 pulse converter. Each thyristor is cooled with deionized water, 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 hung from the ceiling of the valve building of a long distance transmission facility.
Comparisons to other devices
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 TRIACTRIAC
TRIAC, from Triode for Alternating Current, is a genericized tradename for an electronic component that can conduct current in either direction when it is triggered , and is formally called a bidirectional triode thyristor or bilateral triode thyristor.TRIACs belong to the thyristor family and are...
, 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
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
power cycle. Because of this, use of TRIACs with (for example) heavily-inductive
Inductance
In electromagnetism and electronics, inductance is the ability of an inductor to store energy in a magnetic field. Inductors generate an opposing voltage proportional to the rate of change in current in a circuit...
motor loads usually requires the use of a "snubber
Snubber
A snubber is a device used to suppress voltage transients in electrical systems, pressure transients in fluid systems, or excess force or rapid movement in mechanical systems.-Electrical systems:...
" circuit around the TRIAC to assure that it will turn off with each half-cycle of mains power. Inverse parallel
Antiparallel (electronics)
In electronics, two anti-parallel or inverse-parallel devices are connected in parallel but with their polarities reversed.One example is the TRIAC, which is comparable to two thyristors connected back-to-back , but on a single piece of silicon.Two LEDs can be paired this way, so that each protects...
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.
Etymology
An earlier gas filled tubeGas filled tube
A gas-filled tube, also known as a discharge tube, is an arrangement of electrodes in a gas within an insulating, temperature-resistant envelope. Although the envelope is typically glass, power tubes often use ceramics, and military tubes often use glass-lined metal...
device called a Thyratron
Thyratron
A thyratron is a type of gas filled tube used as a high energy electrical switch and controlled rectifier. Triode, tetrode and pentode variations of the thyratron have been manufactured in the past, though most are of the triode design...
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
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
" that the term "thyristor" is derived.
Although thyristors are heavily used in megawatt scale rectification
Rectifier
A rectifier is an electrical device that converts alternating current , which periodically reverses direction, to direct current , which flows in only one direction. The process is known as rectification...
of AC to DC, 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
Power MOSFET
A Power MOSFET is a specific type of metal oxide semiconductor field-effect transistor designed to handle significant power levels. Compared to the other power semiconductor devices , its main advantages are high commutation speed and good efficiency at low voltages...
or IGBTs. One major problem associated with SCRs is that they are not fully controllable switches. The GTO (Gate Turn-off Thyristor) and IGCT
IGCT
The Integrated Gate-Commutated Thyristor is a power semiconductor electronic device, used for switching electric current in industrial equipment. It is related to the gate turn-off thyristor. Like the GTO thyristor, the IGCT is a fully controllable power switch, meaning that it can be turned...
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).
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).
- Switch on dv/dt — the thyristor can be spuriously fired without trigger from the gate if the rate of rise of voltage anode to cathode is too great.
Silicon carbide thyristors
In recent years, some manufacturers have developed thyristors using Silicon carbideSilicon carbide
Silicon carbide , also known as carborundum, is a compound of silicon and carbon with chemical formula SiC. It occurs in nature as the extremely rare mineral moissanite. Silicon carbide powder has been mass-produced since 1893 for use as an abrasive...
(SiC) as the semiconductor material. These have applications in high temperature environments, being capable of operating at temperatures
Operating temperature
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...
up to 350 °C.
Types of thyristor
- AGT — Anode Gate Thyristor — A thyristor with gate on n-type layer near to the anode
- ASCRSilicon-controlled rectifierA silicon-controlled rectifier is a four-layer solid state device that controls current. The name "silicon controlled rectifier" or SCR is General Electric's trade name for a type of thyristor. The SCR was developed by a team of power engineers led by Gordon Hall and commercialized by Frank W...
— Asymmetrical SCR - BCT — Bidirectional Control Thyristor — A bidirectional switching device containing two thyristor structures with separate gate contacts
- BOD — Breakover DiodeDiodeIn electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...
— A gateless thyristor triggered by avalanche current- DIACDIACThe DIAC, or 'diode for alternating current', is a diode that conducts current only after its breakover voltage has been reached momentarily....
— Bidirectional trigger device - Dynistor — Unidirectional switching device
- Shockley diodeShockley diodeThe Shockley diode is a four layer semiconductor diode which was one of the first semiconductor devices invented. It was a "pnpn" diode...
— Unidirectional trigger and switching device - SIDAC — Bidirectional switching device
- TrisilTrisilA Trisil is trade name for a thyristor surge protection device, an electronic component designed to protect electronic circuits against overvoltage...
, SIDACtor — Bidirectional protection devices
- DIAC
- GTO — Gate Turn-Off thyristor
- IGCTIGCTThe Integrated Gate-Commutated Thyristor is a power semiconductor electronic device, used for switching electric current in industrial equipment. It is related to the gate turn-off thyristor. Like the GTO thyristor, the IGCT is a fully controllable power switch, meaning that it can be turned...
— Integrated Gate Commutated Thyristor- DB-GTO — Distributed Buffer Gate Turn-Off thyristor
- MA-GTO — Modified Anode Gate Turn-Off thyristor
- LASCR — Light Activated SCR, or LTT — Light triggered thyristor
- LASS — Light Activated Semiconducting Switch
- MCTMOS Controlled ThyristorMOS Controlled Thyristor is voltage controlled fully controllable thyristor. The MCT is similar in operation with GTO thyristor, but it has voltage controlled insulated gate. It has two MOSFETs in its equivalent circuit. One is responsible for turn-on and the another is responsible for turn-off...
— MOSFET Controlled Thyristor — It contains two additional FET structures for on/off control. - BRTBRTBRT may refer to:* "Be right there" in Internet slang.* Baltic Rubber Trade, Ltd., owner of the BRT trademark.* Bayrak Radyo Televizyon Kurumu is the national public broadcaster of Northern Cyprus....
— Base Resistance Controlled Thyristor - RCT — Reverse Conducting 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 transistorUnijunction transistorA unijunction transistor is an electronic semiconductor device that has only one junction. The UJT has three terminals: an emitter and two bases . The base is formed by lightly doped n-type bar of silicon. Two ohmic contacts B1 and B2 are attached at its ends. The emitter is of p-type and it is...
- SCS — Silicon Controlled Switch or Thyristor Tetrode — A thyristor with both cathode and anode gates
- SCRSilicon-controlled rectifierA silicon-controlled rectifier is a four-layer solid state device that controls current. The name "silicon controlled rectifier" or SCR is General Electric's trade name for a type of thyristor. The SCR was developed by a team of power engineers led by Gordon Hall and commercialized by Frank W...
— Silicon Controlled Rectifier - SITh — Static Induction Thyristor, or FCTh — Field Controlled Thyristor — containing a gate structure that can shut down anode current flow.
- TRIACTRIACTRIAC, from Triode for Alternating Current, is a genericized tradename for an electronic component that can conduct current in either direction when it is triggered , and is formally called a bidirectional triode thyristor or bilateral triode thyristor.TRIACs belong to the thyristor family and are...
— Triode for Alternating Current — A bidirectional switching device containing two thyristor structures with common gate contact
Reverse conducting thyristor
A reverse conducting thyristor (RCT) has an integrated reverse diodeDiode
In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...
, 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
Diode
In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...
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
Frequency changer
A frequency changer or frequency converter is an electronic device that converts alternating current of one frequency to alternating current of another frequency. The device may also change the voltage, but if it does, that is incidental to its principal purpose.Traditionally, these devices were...
s and inverters
Inverter (electrical)
An inverter is an electrical device that converts direct current to alternating current ; the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits....
.
Further reading
- General Electric Corporation, SCR Manual, 6th edition, Prentice-Hall, 1979.
- Dr. Ulrich Nicolai, Dr. Tobias Reimann, Prof. Jürgen Petzoldt, Josef Lutz: Application Manual IGBT and MOSFET Power Modules, 1. Edition, ISLE Verlag, 1998, ISBN 3-932633-24-5 PDF-Version
External links
- The Early History of the Silicon Controlled Rectifier — by Frank William Gutzwiller (of G.E.)
- THYRISTORS — from All About Circuits
- Universal thyristor driving circuit
- Thyristor Resources (simpler explanation)
- Thyristors of STMicroelectronics