Tyristoreita

Tyristorit, known in English as thyristors, are a class of four-layer PNPN semiconductor devices that act as controllable switches in power electronics. They conduct current only after they are triggered by a gate signal and will latch on, continuing to conduct until the current falls below a holding value. This latching behavior allows a small gate current to control large load currents.

The most common form is the silicon-controlled rectifier (SCR), which is unidirectional: it conducts in the forward direction when forward-biased and gated, and blocks reverse voltage. Bidirectional variants, such as triacs, can conduct in both directions once triggered and are widely used for AC power control. Other related devices include gate-turn-off thyristors (GTOs), which can be turned off by a gate signal, and insulated-gate thyristors (IGTs) and related families.

Key characteristics include high blocking voltages, high current handling, and relatively simple gate drive compared with transistor switches. However, once conducting, they act as a fixed-on switch until the current falls below the holding level, which can complicate turn-off and commutation, especially in DC or high-frequency applications. They are sensitive to dv/dt and di/dt, which can cause false triggering if not properly protected.

Typical applications include AC light and motor control, controlled rectifiers and HVDC links, welding power supplies, and power supplies requiring phase control. The technology dates from the 1950s and has evolved with various variants to suit different switching and gating needs.