Commutating device for brushless motor including magnetic diodes

Claim 1

A commutation arrangement for a brushless direct current motor having a rotor and a stator with a plurality of field windings comprising: a plurality of pairs of series connected magnetic diodes, each of said pairs of diodes being associated with one of the field windings of the stator and each pair of diodes being arranged in the stator of the motor so that the resistance of one diode of each pair is decreased while the resistance of the other diode is simultaneously increased under the influence of the magnetic field from the rotor, each of said pairs of magnetic diodes being connected across the operating voltage terminals of the motor to serve as a voltage divider; a plurality of controllable switching means, each of which has its input electrode connected to the center tap of a respective one of said voltage dividers, for connecting the associated field winding across said operating voltage terminals in synchronism with the rotation of the rotor, each of said controllable switching means including a switching transistor, whose base electrode constitutes said input electrode and is connected to the center tap of the associated magnetic diode voltage divider, and a complementary transistor whose base electrode is connected to the collector electrode of said switching transistor, said complementary transistor having its collector-emitter-path connected in series with the one of said field windings which is associated with the associated magnetic diode voltage divider and across said operating voltage terminals, the emitter electrode of said switching transistor being connected to a common emitter bias line; bias control amplifier means, including a further voltage divider means connected across said operating voltage terminals for determining the control voltage of said control amplifier means, for supplying a bias potential to said common emitter bias line for cutting off each of said switching transistors in the absence of an appropriately poled magnetic field being applied to the associated magnetic diode voltage divider; and, automatic means for automatically maintaining the motor speed constant including electronic comparison means for comparing the counter emf generated in said field windings with a predetermined threshold voltage, and comparison responsive means for causing an automatic variation of the division ratio of said voltage divider means to control the emitter potential of said switching transistors to counteract variation in the motor speed.