Patent ID: 7088068

Claim:
A sensorless motor driving apparatus which drives a motor by detecting a position of a rotor by referring to a back electromotive force produced in phase coils and switching between commutation patterns of a driving current in accordance with a result of detection, comprising: a timing generation circuit generating a timing signal at intervals T; a driving signal generation circuit receiving the timing signal and generating, at the intervals T, pulse signals, the number of which M (=m×L+k) is defined by a sum of a predetermined number k, where k is an integer equal to or greater than 1, and a product of a number of statuses L, indicating the number of relative positions of the rotor and the stator, and an integer (m) equal to or greater than 1; and an amplitude control circuit switching between the commutation patterns of the driving signal in synchronization with the pulse signals, wherein said amplitude control circuit advances the commutation pattern by M phases from a predetermined phase, by switching between the patterns in synchronization with the pulse signals while a torque is generated in the motor, advances the commutation pattern by N phases, where N is an integer equal to or greater than 1, by switching between the patterns in synchronization with the pulse signals while a torque is not generated in the motor, and switches the commutation pattern in synchronization with pulse signals with pulse intervals of nT, where n is an integer equal to or greater than 1, while a torque is generated in the motor.