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A thyristor is a four-layer semiconductor switch with three terminals (anode, cathode, and gate) that acts as a bistable switch, meaning it can be in either an "on" or "off" state. It is primarily used for high-power control and is often used in power electronics for applications like motor speed control and AC/DC power switching, as a small gate pulse can control a large current between the anode and cathode.

How it works

Structure: A thyristor has a four-layer, PNPN structure that forms three P-N junctions.

Terminals: It has three terminals: the anode, the cathode, and a gate.

Switching on: When a positive gate signal is applied, the thyristor turns on, allowing current to flow from the anode to the cathode.

Latching: Once turned on, it "latches" in the conducting state and continues to conduct even if the gate signal is removed, as long as the anode-to-cathode current stays above a certain "holding current" threshold.

Switching off: To turn off, the current must be interrupted by reversing the polarity or reducing the voltage below the holding current. Some advanced types, like the Gate Turn-Off (GTO) thyristor, can be turned off with a gate signal.

Key characteristics

High power handling: Thyristors are ideal for high-power applications.

Bistable behavior: They are either fully on or fully off, unlike transistors that can operate in between.

Latching property: They stay on after the trigger is removed, which is a key difference from a transistor.

Control: A small gate current can trigger a much larger anode-to-cathode current.