| 摘要 |
PROBLEM TO BE SOLVED: To obtain a stabilized rotational torque regardless of variation of power supply voltage. SOLUTION: A sensor 15 and a position detecting circuit 17 detect positions where counter-electromotive forces induced in the drive coils of phase U, phase V and phase W forming a brushless motor 11 have the same level. When a power supply voltage being fed from a power supply 21 to the drive coil of each phase is varied with respect to a reference voltage, an inverse proportion circuit 23 outputs a phase shift signal proportional inversely to that variation. A variable phase shift circuit 19 outputs a control signal for switching the drive current to the drive coil of each phase by leading or delaying the phase with respect to a position where the counter-electromotive forces have the same level based on that phase shift signal. A drive circuit 25 conducts the drive current to the drive coil while switching by that switching control signal. |
