Page 439 - Power Electronics Handbook

428 Glossary of terms

Thermal runaway: A mechanism within a semiconductor in which the
power increase results in a build-up of temperature which further increases
the power, so that the device is rapidly destroyed.
Trigger circuit: See Firing circuit.
UJT: Unijunction transistor. Trigger device used to control power
semiconductors.
Voltage multiplier: A circuit which produces an output voltage which has a
magnitude several times that of the input.
Waveform synthesis: A method for controlling the output voltage from an
inverter, to approximate it to a sine wave and so reduce the amount of
harmonics.
Zero crossing control: A technique for detecting the occurrence of the zero
voltage points in the input a.c. voltage and of turning on the power
switches at these instances, so as to minimise the peak voltage at which the
devices switch and therefore reduce the generated radio frequency
interference.