What Is a Silicon Controlled Rectifier?
A silicon controlled rectifier (SCR) is a semiconductor device designed to switch and control high current loads. The SCR is essentially a current controller which relies on an externally supplied trigger voltage to switch on. SCR devices also feature a preset holding current value below which they will not conduct even if switched on. This allows for controlling when the device switches on and the minimum current it will pass. Silicon controlled rectifiers are typically used in high current, high voltage application although they are often found in lower voltage systems such as lamp dimmers. SCRs consist of four alternating layers of p and n semiconductor materials. An external lead, known as the gate, is connected to the second p layer. The gate is used to supply the trigger voltage which causes the SCR to turn on and start conducting. The semiconductor wafers are formed into a compact pellet contained in a molybdenum or tungsten casing. The casing is fitted with a threaded stud on o
