) 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:

By selecting an appropriate value of V < sub > G </ sub >, the thyristor can be switched into the on state suddenly.

After the current in a thyristor has extinguished, a finite time delay must elapse before the anode can again be positively biased and retain the thyristor in the off-state.

Two of three thyristor valve stacks used for long distance transmission of power from Manitoba Hydro damsSince 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.

* 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.

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.

Both classes can switch higher energy levels than any thyristor, thyratron, krytron, or sprytron.

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 ( turned on ), and is formally called a bidirectional triode thyristor or bilateral triode thyristor.

The unique whine of the motors and gear assemblies can lead many to mistake the cars for using thyristor drive or even a variable-frequency drive, but this is not the case.

Like the GTO thyristor, the IGCT is a fully controllable power switch, meaning that it can be turned both on and off by its control terminal ( the gate ).

This pole uses thyristor valves in its static inverters and can transfer at an operating voltage of 280 kV with a maximum power of 370 megawatts.

For power semiconductor devices ( such as BJT, MOSFET, thyristor or IGBT ), the safe operating area ( SOA ) is defined as the voltage and current conditions over which the device can be expected to operate without self-damage.

This combination can be used to suppress the rapid rise in voltage across a thyristor, preventing the erroneous turn-on of the thyristor ; it does this by limiting the rate of rise in voltage ( dV / dt ) across the thyristor to a value which will not trigger it.

The thyristor valves are usually grouped in pairs or groups of four and can stand on insulators on the floor or hang from insulators from the ceiling.

Howevever, under the proper circumstances ( of both circuit design, process design, and particle properties ) a " parasitic " thyristor inherent to CMOS designs can be activated, effectively causing an apparent short-circuit from power to ground.

The applications for the device were initially regarded by the power electronics community to be severely restricted by its slow switching speed and latch-up of the parasitic thyristor structure inherent within the device.

Successful efforts to suppress the latch-up of the parasitic thyristor and the scaling of the voltage rating of the devices at GE allowed the introduction of commercial devices in 1983, which could be utilized for a wide variety of applications.

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.

One disadvantage of the thyristor for switching circuits is that once it is ' latched-on ' in the conducting state it cannot be turned off by external control.

The thyristor turn-off is passive, i. e., the power must be disconnected from the device.

Mercury arc rectifiers are usually supported by insulators mounted on the floor, while thyristor valves may be either supported by insulators or hung from the roof of the valve hall.

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 ( I < sub > L </ sub >).

One-line diagram of a typical SVC configuration ; here employing a thyristor controlled reactor, a thyristor switched capacitor, a harmonic filter, a mechanically switched capacitor and a mechanically switched reactor

* In 1989, a further increase of the transmission power took place by a parallel switched thyristor static converter in Celilo and Sylmar.

Each station's static inverter, which is switched as a 12-pulse thyristor bridge, consists of 792 thyristors arranged in three high towers installed in a valve hall.

Active crowbars use a transistor, gate turn off ( GTO ) thyristor or forced commutated thyristor instead of a thyristor to short the circuit.

Now if V < sub > AK </ sub > is increased beyond the breakdown voltage V < sub > BO </ sub > of the thyristor, avalanche breakdown of J < sub > 2 </ sub > takes place and the thyristor starts conducting ( On state ).

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 ).

* Universal thyristor driving circuit

In principle, it is easy to design silent switches in which the mechanical contacts do not directly control the current, but simply signal a solid-state device such as a thyristor to complete the circuit.

A thyristor drive is a motor drive circuit where AC supply current is regulated by a thyristor phase control to provide variable voltage to a DC motor.

A capacitor is charged by a solid-state circuit – upon contact with a grounded animal or person, the charge is then released using a thyristor or similar solid-state component.

Like the thyristor it consists of four P-N layers and has an anode and a cathode connected to the first and the last layer, and a gate connected to one of the inner layers.

The thyristor has three p-n junctions ( serially named J < sub > 1 </ sub >, J < sub > 2 </ sub >, J < sub > 3 </ sub > from the anode ).

Once avalanche breakdown has occurred, the thyristor continues to conduct, irrespective of the gate voltage, until: ( a ) the potential V < sub > AK </ sub > is removed or ( b ) the current through the device ( anode − cathode ) is less than the holding current specified by the manufacturer.

* AGT — Anode Gate Thyristor — A thyristor with gate on n-type layer near to the anode

* 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

* SCS — Silicon Controlled Switch or Thyristor Tetrode — A thyristor with both cathode and anode gates

# 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 "

These are known as RCT, for reverse conducting thyristor.

A solid-state device with similar operating characteristics is the thyristor, sometimes also known as the silicon controlled rectifier ( SCR ).