Silicon Controlled Rectifier (SCR) Symbol

A silicon-controlled rectifier (SCR) is a type of thyristor device with three terminals used in switching applications. A positive voltage at the gate junction enables current to flow between the anode and cathode junctions. The current will flow only in one direction, and once the device is conducting, removal of the gate voltage does not affect this current flow. To turn OFF this conduction, the anode has to be more negative than the cathode; alternatively, momentary removal of anode to cathode current flow will also switch OFF the conduction.