Importance

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Abstract

A drive circuit for a sensorless three-phase brushless DC motor provides improved drive characteristics by generating a pseudo back-electromotive signal in response to the voltages of the stator coils, and then using the pseudo back-electromotive signal to commutate the current through the stator coils before maximums in the back electromotive force, thereby providing smoother motor rotation. The drive circuit includes comparators for generating rectangular difference signals by comparing the voltages of the stator coils, an edge detector and control circuit for generating a pulse signal that is delayed from the difference signals, signal generators for generating a trapezoidal signal and three step signals responsive to the pulse signal, and an output control circuit for generating drive signals for a commutator drive circuit responsive to the trapezoidal step signals. By setting the voltage differences between the trapezoidal and step signals to values less than the Hall bias level, the drive signals can be made to change linearly, thereby providing soft switching of the transistor switches in the commutator drive circuit.

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First Claim