Control circuit for dc brushless motor producing constant output torque

Abstract

A control circuit for controlling a multi-phase brushless DC motor to produce a constant level of torque employs one Hall generator for each pair of armature windings corresponding to a motor phase, with each Hall generator being arranged to produce output signals whose timings determine the respective timings of switching of current to the armature windings and whose amplitudes are detected to produce a signal representing motor torque. This is achieved by passing currents through each Hall generator which are held proportional to currents flowing in the corresponding armature windings, so that the amplitudes of output voltage signals produced by the Hall generators represent the product of magnetic flux density of field magnet flux linked to the armature windings and armature winding current, and so are proportional to the torque.