Electrical motor with a differential phase back emf sensing circuit for

Abstract

A motor having a differential phase back EMF sensing circuit for sensing rotor position includes a stationary assembly with at least three windings. The rotation of the rotor induces a back EMF in the windings. A control circuit energizes each of the windings with a current according to a preselected sequence. A switch network is coupled to the windings and provides two back EMF signals as a function of the back EMF induced in two of the windings when the control circuit is energizing the third winding. A signal processor is coupled to the switch network and produces a difference signal representative of a difference between the two back EMF signals. An integrator integrates the difference signal to produce an integrated difference signal. The motor includes a reference signal generator which produces a reference signal and a comparator which produces a trigger signal when the integrated difference signal exceeds the reference signal. The motor also includes a one shot which produces a position signal as a function of the trigger signal and a position counter which produces a position count signal as a function of the position signal. The control circuit energizes each of the windings according to the preselected sequence as a function of the position count signal. Other circuits and methods control the motor. The trigger signal may be generated in response to a zero crossing detector and timer.