ABSTRACT
This chapter discusses controls in which the current through the coils is held approximately constant, instead of the voltage. One type of constant-current design is referred to as a "chopper" circuit. When the current reaches a predetermined limit, the voltage is "chopped" off and the current drops. The advantage is that motors can be driven at higher speeds and torques than in constant-voltage circuits. In the context of motor controls, a chopper circuit is one in which a controlled switch is used to limit the current flowing through a coil. The operation requires some way of sensing the current so that the chopper switch can be turned on and off as the predetermined current limits are reached. Chopper circuits can also be used with unipolar motors, although bipolar ones are by far more common. The Allegro SLA7024M is a chopper control IC for unipolar motors.
