A silicon controlled rectifier, commonly called an SCR, is a solid-state device used to control current.
SCRs consist of four layers of semiconductors to form alternating p- and n-type junctions. Their construction allows for one-way current switching. In the off state, the SCR offers a very high resistance until applied voltage reaches the device's breakover value. In the on state, the SCR is conducting until current is reduced or the cathode and anode are momentarily shorted with a switch across the junction.
SCRs are mainly used in high power, high voltage applications like power regulators, motor controllers, and rectification in high voltage DC power transmission.