In a DC motor driven by sinewave power-on driving and having hall elements shift-mounted
relative to a stator for detecting the position of a rotor, a reduction in starting
torque is eliminated by avoiding a braking action occurring when switching phases
on starting the motor. In the case of the sinewave power-on driving, the braking
action may occur owing to delay of the current flowing through the windings of
the motor by the influence of an inductance value of stator windings and induced
voltage of the motor. In order to avoid the braking action, hall elements for detecting
the position of the rotor are shift-mounted. However, the braking action would
be likely to occur on the contrary, because the induced voltage is low when the
motor is started. To solve this problem, according to the invention the 120
rectangular wave power-on driving is executed for starting the motor until the
number of revolutions of the motor has attained a predetermined value after starting,
thereby reducing the undesirable braking action.
