Unitrode Corporation

David S Zendzian

Robert Allan Neidorff

John A O'Connor

A brushless DC motor controller including a track and hold circuit responsive to the voltage at the motor centertap terminal and the voltage across at least one motor winding in order to determine the position of the rotor by detecting zero crossings of the back EMF of the unenergized winding in a manner having reduced susceptibility to noise. In one embodiment, the output of the track and hold circuit is interpolated to reduce the effects of pulse width modulation noise on rotor position detection. The drive signals controlling a plurality of electronically controlled switches which effect energization of the windings are chopped in order to control the speed of the motor. In one embodiment, the switch connected to a positive voltage is chopped when the sensed back EMF is positive and the switch connected to the negative voltage is chopped when the sensed back EMF is negative. Also provided is a PWM disable circuit for selectively disabling a PWM signal used to chop the drive signals in order to further reduce the effects of noise on rotor position detection.

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Merrimack, NH, United States of America

David S Zendzian