Patent ID: 8089232
Filing Date: 2012-01-03
Classification: G11B,H02P

Abstract:
1. A motor drive device that switches a current to flow in each of phases of a brushless motor having a plurality of coils and drives said brushless motor, the motor drive device comprising: a motor drive control mechanism that performs control processing by switching between a first mode of soft switching control with an asynchronous PWM carrier signal independent of the number of revolutions of said brushless motor and a second mode of soft switching control with a synchronous PWM carrier signal synchronized with the number of revolutions of said brushless motor, wherein said motor drive control mechanism comprises: a common arithmetic unit that executes an arithmetic operation for a PLL control loop for said brushless motor, an arithmetic operation for a current control loop, and an arithmetic operation for soft switching control to suppress a steep change in current; a turn-on timing counter that generates a conducting phase signal from a result of the arithmetic operation for a PLL control loop; an output controller that generates a PWM signal to control a current to be supplied to said brushless motor; and a control unit that detects the number of revolutions of said brushless motor, wherein said control unit activates, when the number of revolutions of said brushless motor is less than the number of steady revolutions, a synchronization/no synchronization control signal indicating whether to synchronize the PWM carrier signal frequency with the number of revolutions of said brushless motor or fix the frequency, and deactivates said synchronization/no synchronization control signal when the number of revolutions of said brushless motor has reached the number of steady revolutions, and wherein said common arithmetic unit detects whether a division control signal which is a synchronous PWM carrier signal count value generated by said turn-on timing counter has changed when said synchronization/no synchronization control signal is active, and executes soft switch arithmetic upon detecting a change of said division control signal.