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A drive is the power electronics board which is used to control the speed of a motor. Drives may use various techniques to control speed.
A low-cost form of drive for controlling DC motors makes use of a special type of power transistor called an SCR. Hence the term SCR drive .
An SCR acts as a gate to allow a precise amount of current to flow to the motor. Through feedback systems, this current also controls the voltage allowed to generate the armature field of the motor, and thus the speed is controlled.
SCR drives are most commonly used to control DC motors, but the system is also used in some older AC inverter drives controlling AC motors. SCR's are being used less and less in AC inverter drives because of the greater reliability provided by another newer type of transistor, the Insulated Gate Bipolar Transistor (IGBT).
Copyright 1997, Brian L. Boley All Rights Reserved.