| 摘要 |
PROBLEM TO BE SOLVED: To drive at a low rotating speed while preventing occurrence of loss of synchronism, in a driving device for a brushless motor designed such that two phases for applying a pulse voltage corresponding to a pulse width modulation signal among three phases are switched according to position information based on a pulse induction voltage, which is induced in a non-energization phase.SOLUTION: A duty ratio per N (N is an integer of 1 or greater) time or times of a pulse width modulation period is made not to fall below the lowest duty ratio. The value of the N is changed in an increasing direction according to a decrease in the rotating speed of a motor. Position information is captured at a period by which the duty ratio is limited to the lowest duty ratio. When the rotating speed of the motor cannot be decreased below a target rotating speed even if an average duty ratio is set to the lowest average duty ratio, an electrical angle, which is a switching period for an energization mode, is switched from 60 degrees to 120 degrees. |
