Page 438 - Power Electronics Handbook

Glossary of terms 427

pnlse-width modnlption: A method for varying the mark-to-space ratio of
the output voltage waveform during a cycle so as to minimise the
magnitude of the harmonics in the output.
Push-pull converter: An arrangement for a power converter which uses a
centre-tapped load. (See also Bridge converter.)
PUR Programmable unijunction transistor. Unijunction transistor whose
trigger point can be controlled by external components.
Regenerative gate: A thyristor structure which enables it to handle high
rates of current rise.
Reverse recovery time: The time needed for a forward-conducting device to
regain its blocking capability after it has been reverse biased. During this
period its impedance is low and it can pass a large amount of reverse
recovery current.
RF'I: Radio frequency interference. The unwanted interference caused by
equipment which radiates electromagnetic waves.
Ripple current: The a.c. component of current present on a d.c. supply,
which has not been removed by filtering.
Safe operating area: The current and voltage area of a power transistor
characteristic in which it must remain if it is to avoid thermal runaway. (See
Thermal runaway.)
SCR: Silicon controlled rectifier. Original term used for a thyristor.
Shorted emitter: A thyristor construction technique which enables it to
withstand rapid rate of rise of voltage across it.
SMR Surface mount technology. Usually refers to components which are
soldered onto a board without the use of leads which go through the
board.
Snubber circuit: A resistor-capacitor circuit connected so as to prevent the
voltage from rising too rapidly across the power semiconductor.
SOA: Safe operating area. The area, defined by current and voltage, in which
a power semiconductor can operate.
SOIC: Small outline integrated circuit. A style of surface mount integrated
circuit package.
Staggered phase carrier cancellation: A method of voltage control for an
inverter in which the a.c. harmonics in the output are reduced.
Surge suppressor: A device which limits the value of the maximum voltage
across a power semiconductor.
SUS: Silicon unilateral switch. Power semiconductor control device.
TAB: Tape automated bonding. Use of a flexible carrier tape to connect the
silicon chip to the package or substrate.
Thermal resistance: A measure of the increase in temperature of the
semiconductor junction as the power dissipation within it increases.