A semiconductor component that is unidirectional like a diode, but is switched like a transistor. It is widely used to control high currents and voltages in motors, lighting, heating and power applications. Once turned on at the gate, it allows current to flow until it falls below a certain threshold. In an AC circuit, it stops conducting each time the wave crosses over zero and can rectify AC to DC. See diode
, PN junction
and n-type silicon
A thyristor is like two diodes in a row with a third terminal (the gate). When voltage is applied to the gate, current flows from the anode to the cathode until the current falls below a certain threshold.