Controlled rectifier

(electronics) A rectifier that has provisions for regulating output current, such as with thyratrons, ignitrons, or silicon controlled rectifiers.

A three-terminal semiconductor junction device with four regions of alternating conductivity type (p-n-p-n), also called a thyristor. This switching device has a characteristic such that, once it conducts, the voltage in the circuit in which it conducts must drop below a threshold before the controlled rectifier regains control. Such devices are useful as high-current switches and may be used to drive electromagnets and relays.

The principle of operation can be understood by referring to the illustration. The central junction is reverse-biased (positive collector, grounded emitter). The wide n region between collector and base regions prevents holes injected at the collector junction from reaching the collector-to-base barrier by diffusion. The junction between emitter and base is the emitter. When operated as a normal transistor, this device shows a rapid increase of current gain with collector current. This effect may be due to a field-induced increase of transport efficiency across the floating n region, or to increased avalanching in the high-field barrier region, or to increased injection efficiency at the two forward-biased junctions, or to a combination of these phenomena.

Diagram of a controlled rectifier.

If this device is operated as a three-terminal device, the switching between the nonconducting and conducting states can be controlled by the base. See also Semiconductor rectifier.