Single phase brushless motor fed from DC source - with induced voltage in windings used as feedback dependent on speed

摘要

In the motor, with a permanent magnet rotor, the windings are alternately switched to a dc source to give in effect a single phase supply to the machine. A reluctance motor effect provides torque during the winding commutation period. The voltage induced in the windings by the permanent magnets is picked off and used as a speed feedback. Where npn transistors are used in the commutating circuit the feedback signal performance can be improved by placing a diode (3, 4) in the voltage tappings from the windings (1, 2). The tapping common point (31) is connected (28) through a further diode (15) to the speed sensor and controller. This connection (28) is also joined to the dc positive rail by a diode (14). The effect of the diode voltage drops is to increase the period during which the positive supply voltage is applied to the feedback and thus allow more time for commutation without interfering with the feedback signal.