Editing Thyristor (section)

== Applications ==
[[File:Regulated rectifier.gif|thumb|Waveforms in a rectified multiple thyristor circuit controlling an AC current.<br />Red trace: load (output) voltage<br />Blue trace: trigger voltage]]

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 circuit|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]].

They can also be found in power supplies for [[digital electronics|digital circuits]], where they are used as a sort of "enhanced [[circuit breaker]]" 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 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 (electrical)|fuse]]). This kind of protection circuit is known as a [[Crowbar (circuit)|crowbar]], and has the advantage over a standard circuit breaker or fuse in that it creates a high-conductance path to ground from 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]] receivers in the early 1970s.{{clarify|reason=Verb missing. 'DIAC' or 'DIACs'? Etc.|date=April 2015}}  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]], [[motion picture]]s, and [[theater]], where they replaced inferior technologies such as [[autotransformer]]s and [[rheostat]]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.<ref>{{Cite web|url=https://www.electronicsmind.com/2021/12/didt-and-dvdt-ratings-and-protection-of-scr-or-thyristor.html|title=di/dt and dv/dt Ratings and Protection of SCR or Thyristor|date=5 December 2021|website=Electronics Mind}}</ref>

This is prevented by connecting a [[resistor]]-[[capacitor]] (RC) [[snubber]] 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 ===
[[File:Manitoba Hydro-BipoleII Valve.jpg|thumb|upright|[[Valve hall]] containing [[thyristor valve]] stacks used for long-distance transmission of power from [[Manitoba Hydro]] dams]]

Since modern thyristors can switch power on the scale of [[megawatt]]s, 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,{{r|:0|pp=12}} both electrically triggered (ETT) and light-triggered (LTT) thyristors<ref>{{cite book| url=http://www.siemens.co.in/pool/about_us/our_business_segments/hvdc_proven_technology.pdf |title=High Voltage Direct Current Transmission&nbsp;– Proven Technology for Power Exchange |publisher=[[Siemens]] |chapter=Chapter 5.1 |access-date=2013-08-04}}</ref><ref>{{cite journal |url=https://library.e.abb.com/public/3c981b9078f55447c1256feb0022602a/ETT%20vs%20LTT.pdf|title=ETT vs. LTT for HVDC | publisher=[[ABB Asea Brown Boveri]] |access-date=2014-01-24}}</ref> are still the primary choice. Thyristors are arranged into a [[diode bridge]] circuit and to reduce [[Harmonics (electrical power)|harmonics]] are connected in series to form a [[Rectifier#Twelve-pulse_bridge|12-pulse converter]]. Each thyristor is cooled with [[Distilled water#Deionization|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 mounted on the floor or hung from the ceiling of the [[valve hall]] of a long-distance transmission facility.<ref>{{cite journal |url=http://www.abb.com/cawp/gad02181/c1256d71001e0037c12568320068995e.aspx |title=HVDC Thyristor Valves |publisher=[[ABB Asea Brown Boveri]] |access-date=2008-12-20 |url-status=dead |archive-url=https://web.archive.org/web/20090122071434/http://www.abb.com/cawp/gad02181/c1256d71001e0037c12568320068995e.aspx |archive-date=January 22, 2009 }}</ref><ref>{{cite journal|url=http://kn.theiet.org/magazine/issues/0809/high-power.cfm |title=High Power |publisher=[[Institution of Engineering and Technology|IET]] |access-date=2009-07-12 |url-status=dead |archive-url=https://web.archive.org/web/20090910162625/http://kn.theiet.org/magazine/issues/0809/high-power.cfm |archive-date=September 10, 2009 }}</ref>