Patent ID: 7855521

Claim:
A motor drive circuit which supplies drive current and drives a multi-phase motor, the motor drive circuit comprising: a plurality of switching circuits provided for respective coils of the multi-phase motor and operative to apply a voltage of high level or low level to one end of the coil; a pulse modulation signal generation unit which generates a pulse modulation signal whose duty ratio changes according to a target torque of the multi-phase motor, and outputs a reference signal that becomes a predetermined level at a predetermined timing; a back electromotive detection circuit which detects a zero crossing point by comparing a back electromotive voltage generated in at least one coil of the multi-phase motor with a middle point voltage of the coil, and outputs a back electromotive detection signal that becomes a predetermined level at a timing of the zero crossing point; a switching control unit which receives the pulse modulation signal from the pulse modulation signal generation unit and the back electromotive detection signal from the back electromotive detection circuit, and switch controls at least one of a high side switch or a low side switch contained in the switching circuit to be driven based on the back electromotive detection signal; and a pulse adjustment unit which adjusts a frequency of the pulse modulation signal based on the reference signal and the back electromotive detection signal.