Page 435 - Power Electronics Handbook

424 Glossary of terms
Commutation process: The process of transferring current from one
element to another, for example from one coil to another in a d.c.
machine. Usually refers to the process used to turn off a power
semiconductor by transferring the load current to a commutation diode.
Controlled rectification: The process of regulating the amount of power
which flows from an a.c. supply to a d.c. load, this usually being achieved
by bridge or push-pull connected converters.

Crowbar circuit: A circuit used to protect the load from overvoltages
resulting from a d.c. supply by shorting the output of the supply when
overvoltages are detected.

CU JT Complementary unijunction transistor. Trigger device used to control
power semiconductors.
Current-fed inverter: A d.c. to a.c. converter which uses a high-valued
reactor in the supply line, such that the current from the d.c. supply is
substantially constant.
Cycloconverter: A frequency changer which converts a.c. at one frequency
to a second, lower, frequency, without first going through a rectification
stage. This is also referred to as a direct a.c. frequency converter.
Cycloinverter: A frequency changer which converts a.c. at one frequency
to a second, higher, frequency, without first going through a rectification
stage.
D.C. link frequency changer: See Inverter.
DCA: Direct chip attach. Process for connecting a semiconductor dice onto
the substrate without first packaging it. Used in hybrid circuits and multichip
modules.
Delay angle: The delay between the start in conduction of a power
semiconductor and the instance when the supply voltage across it begins to
go positive. This is also referred to a phase-control angle or firing angle.
Depletion layer: The layer between a p-type and n-type region in a
semiconductor which has very few free charge carriers.
Wdf: The rate of change of current through a power semiconductor which,
if it exceeds a certain maximum value, could destroy the device.
Doping: The process of adding impurities to a semiconductor to produce a
p-type or n-type material.
dv/dt: The rate of rise of voltage across a power semiconductor which, if
exceeded, could cause it to turn-on.
EMC: Electromagnetic compatibility. Used to refer to the process of
controlling the effects of radio frequency interference.
EPAS: Electrical power assisted steering. Control system used on cars to
reduce the effort needed in steering.
ESD: Electrostatic discharge. The discharge of static electricity, which often
destroys semiconductors.