Patent ID: 6979970

Claim:
A sensorless motor driving device comprising: an output circuit energizing a motor coil of a sensorless motor; a PWM control section generating a PWM control signal showing a timing of the energization of said motor coil, based on a position signal showing an estimated rotor position of said sensorless motor; an energization phase switching circuit switching between energization phases in synchronization with a commutation signal; a pre-drive circuit selecting said motor coil corresponding to said energization phase, changing the energization of the selected motor coil through said output circuit according to said PWM control signal, and, disabling the energization of the specific motor coil by said output circuit in a PWM disable period; a BEMF comparing section detecting a BEMF (back electromotive force) induced in said motor coil and comparing said BEMF with a center tap voltage of said motor coil; a self-commutation circuit detecting agreement between said BEMF and said center tap voltage, that is, a zero crossing during a BEMF detection period, and generating a self-commutation signal when detecting the zero crossing; and a count section generating said commutation signal based on said self-commutation signal, measuring an interval of said commutation signal, generating said position signal based on the interval, establishing said PWM disable period and said BEMF detection period based on said position signal, and starting said PWM disable period earlier than the start of said BEMF detection period and finishing both of said PWM disable period and said BEMF detection period in synchronization with said commutation signal.