Drive circuit for a brushless motor

H - Electricity – 02 – P

Patent

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318/96

H02P 5/00 (2006.01)

Patent

CA 1107815

ABSTRACT A drive circuit for a brushless motor which includes rotor position sensors for generating varying signals correspond- ing to the rotary position. Amplifier stages are coupled to the position sensors, the amplifier stages being responsive to the position signals produce drive currents which are supplied to the stator windings. In one embodiment, each amplifier stage includes a voltage amplifier having a linear gain charac- teristic for amplifying the position signal applied thereto, a current amplifier connected in cascade with the voltage amplifier and responsive to the amplified position signal to produce a drive current. A feedback circuit is interconnected between the output of the current amplifier and the input to the voltage amplifier. The feedback circuit includes a low pass filter circuit to prevent harmonics of the drive current fre- quency from being transmitted to the stator winding, thereby preventing notching in the drive current. In another embodiment, the drive circuit also includes a speed sensor, a converter coupled to the speed sensor for converting the frequency of the generated signal to a voltage. A circuit applies the converted voltage to the position sensors so as to modify the position signals in accordance with the sensed motor speed. A circuit supplies an offset voltage to the last-mentioned circuit such that if the speed of the motor exceeds a predetermined amount, the offset voltage exceeds the converted voltage whereby the result- ant voltage which is applied to the position sensors causes a modification in the drive currents supplied to the stator wind- ings, to produce an opposite torque in the motor. In this embodi- ment, excess motor speeds are rapidly corrected.

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