Thyristors
A thyristor is a type of semiconductor device that acts like a switch, allowing energy to flow in one direction only. It is a three-terminal electronic device composed of four layers of alternating P-type and N-type material that can operate in four different states: off, forward blocking, reverse blocking, and forward conducting. In its off state, the thyristor does not conduct current; in its forward blocking state, it allows current to flow in the forward direction only; in its reverse blocking state, it allows current to flow in the reverse direction only; and in its forward conducting state, it allows current to flow in either the forward or reverse direction. Thyristors can be used in many applications such as power control, over-current protection, motor speed control, and lighting dimmers.