Thyristors – SCRs (Silicon-Controlled Rectifiers) are a type of semiconductor device used for power control and switching applications. They are unidirectional devices that allow current to flow in one direction while blocking it in the other. SCRs consist of four layers of semiconductor material, with each layer having a different electrical charge. When a signal is applied to the gate terminal, the SCR switches on, allowing current to flow between the anode and cathode terminals. Once triggered, the SCR remains on until the current through the device falls below a certain level or a reverse voltage is applied. SCRs are commonly used in motor control, lighting systems, and power supplies due to their high efficiency and fast switching times.