The word thyristor comes from the Greek and means "door," as in
opening a door and letting something pass through it. A thyristor is a
semiconductor device that uses internal feedback to produce
switching action. The most important thyristors are the silicon
controlled rectifier (SCR) and the triac. Like power FETs, the SCR and
the triac can switch large currents on and off. Because of this, they
can be used for overvoltage protection, motor controls, heaters,
lighting systems, and other heavy-current loads. Insulated-gate
bipolar transistors (IGBTs) are not included in the thyristor family, but
are covered in this chapter as an important power-switching device.
