The silicon-controlled rectifier (SCR) is a semiconductor device that acts as a switch capable of controlling high power and voltage. When an SCR is turned on by applying a gate signal, it allows current to flow between its anode and cathode, effectively acting as a short circuit. This characteristic makes it useful in a variety of applications, including light dimmers, motor speed controls, and power regulators.
To turn off an SCR, the current flowing through it must drop below a certain threshold, or the gate trigger needs to be removed. The unique design of the SCR allows it to remain on even after the gate signal is removed, maintaining the low-resistance path (short circuit) until the current is interrupted. This is unlike other components; for instance, a transistor can be turned off by changing the base current, and a diode conducts in one direction but does not have the capability to turn off based on a direct gate trigger. Additionally, a relay uses mechanical contacts to open and close circuits rather than the semiconductor principles that govern SCR operation.
This distinctive switching mechanism and the ability to control significant currents and voltages make the SCR the correct choice in this context.