Patent ID: 6586898
Filing Date: 2003-07-01
Classification: H02P

Abstract:
An electromotive force (EMF) detection circuit that provides an indication of a position of a rotor in an electric motor with at least a first unipolar winding and a second unipolar winding, the EMF detection circuit comprising:a first sense circuit connected to a first transistor and a second transistor, where the first transistor is configured to energize a first portion of the first unipolar winding and the second transistor is configured to energize a second portion of the first unipolar winding, and where the first sense circuit detects a first EMF associated with the first unipolar winding; a second sense circuit connected to a third transistor and a fourth transistor, where the third transistor is configured to energize a first portion of the second unipolar winding and the fourth transistor is configured to energize a second portion of the second unipolar winding, and where the second sense circuit detects a second EMF associated with the second unipolar winding; a combiner circuit adapted to generate an output responsive to a difference in the first EMF detected by the first sense circuit and the second EMF detected by the second sense circuit; and a comparator circuit coupled to the output of the combiner circuit, the comparator circuit configured to generate a PWM commutation signal when the electric motor is operated in a PWM mode and to generate a commutation signal corresponding to a first EMF phase when the electric motor is operated in a non-PWM mode, where the comparator circuit is further configured to provide a filtered signal that provides an output that is approximately proportional to displacement of the rotor, rather than to the EMF phase.