Brushless d.c. motor having permanent magnet rotor and hall effect commutation including speed control responsive to winding voltage

Claim 1

A brushless DC motor having a permanent magnet rotor and Hall effect generator control, said motor being powered by a DC voltage source having a first and a second terminal, the motor having a stator winding having four winding branches mutually displaced electrically by 90*, the winding branches having one end which is Y-connected and is connected directly to the first terminal of the DC voltage source and another end, a plurality of power transistors each having emitter, collector and base electrodes and a collector-emitter path, the other end of each of the winding branches being connected to the second terminal of the DC voltage source via the collector-emitter path of a corresponding one of the power transistors, a plurality of input transistors of opposite conductivity type from the power transistors and each having emitter, collector and base electrodes, the collector electrode of each of the input transistors being connected to the base electrode of a corresponding one of the power transistors, a plurality of first collector resistors, the collector electrode of each of the input transistors being connected to the second terminal of the DC voltage source via a corresponding one of the first collector resistors, a common emitter resistor, the emitter electrodes of the input transistors being connected to the first terminal of the DC voltage source via the common emitter resistor, a pair of Hall effect generators each having a pair of Hall voltage electrodes and a pair of control current electrodes, the base electrodes of two input transistors connected to the power transistors connected to two winding branches mutually displaced electrically by 180* being connected to the Hall voltage electrodes of a corresponding one of the Hall effect generators, resistor means, the control current electrodes of the Hall effect generator being connected to the first and second terminals of the DC voltage source via the resistor means, a plurality of coupling transistors each having emitter, collector and base electrodes and an emitter-base path for deriving from the winding branches a voltage proportional to the speed of rotation of the rotor, the coupling transistors being connected to each other and to the first terminal of the DC voltage source, and a comparator circuit connected to the coupling transistors, said brushless motor comprising switching means coupled to and controlled in condition by the comparator circuit; means connecting the control current terminals of the Hall effect generators to the second terminal of the DC voltage source through the switching means; means connecting the base electrodes of the coupling transistors to each other; means connecting each pair of the coupling transistors to a corresponding pair of the winding branches which are mutually displaced electrically by 180*; and means connecting the collector electrode of each coupling transistor of a pair of coupling transistors to the base electrode of the power transistor connected to the other of the corresponding pair of winding branches, the voltage proportional to the speed of rotation of the rotor at the emitter-base paths of the coupling transistors being provided at the winding branches.