Patent ID: 7609013

Claim:
A motor drive circuit which supplies a drive current in a pulse form to a multiphase motor, to drive the motor, the circuit comprising: a pulse signal generation circuit which generates a pulse signal having a duty ratio in accordance with torque; plural switching circuits which are provided for every coil of the multiphase motor, and which alternately repeat an ON time-period and an OFF time-period, to supply a drive current in a pulse form to an end of a connected coil, in accordance with the pulse signal from the pulse signal generation circuit; a back electromotive force detection circuit which compares a back electromotive voltage occurring in at least one coil of the multiphase motor, with a midpoint voltage of the coil, to detect a zero-cross point, and which outputs a back electromotive force detection signal; and a switching control circuit which controls drive sequence of the plural switching circuits, based on the back electromotive force detection signal from the back electromotive force detection circuit; wherein the back electromotive force detection circuit uses, at least, the back electromotive voltage of the ON time-period to interpolate the back electromotive voltage of the OFF time-period, and detects the zero-cross point, based on voltage in accordance with an interpolated virtual back electromotive voltage and the midpoint voltage of the coil.