TABLE OF CONTENTS Thyristors are usually three-terminal devices that have four layers of alternating p-type and n-type material (i.e. three p n junctions) comprising its main power handling section. In contrast to the linear relation which exists between load and control currents in a transistor, the thyristor is bistable. The control terminal of the thyristor, called the gate ( G) electrode, may be connected to an integrated and complex structure as a part of the device. The other two terminals, called the anode ( A) and cathode ( K), handle the large applied potentials (often of both polarities) and conduct the major current through the thyristor. The anode and cathode terminals are connected in series with the load to which power is to be controlled.
Thyristors are used to approximate ideal closed (no voltage drop between anode and cathode) or open (no anode current flow) switches for control of power flow in a circuit. This differs from low-level digital switching circuits that are designed to deliver two distinct small voltage levels while conducting small currents (ideally zero). Thyristor circuits must have the capability...
