| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide the driver of a brushless motor in which shutdown due to step-out is distinguished from shotdown due to fault by informing the step-out state of the brushless motor to a user, and the user can restart the brushless motor, and to provide a power tool. <P>SOLUTION: A control circuit 1c detects step-out state from the time interval of a position detection signal S2, turns a switching element Q2 on continuously when the step-out state is detected, and turns a switching element Q5 on/off repeatedly by PWM control to feed motor drive coils 2w and 2u with a PWM controlled motor current containing a ripple component thus performing DC excitation. Since the strength of a magnetic field being generated in a stator 2 is varied at the PWM frequency, the stator 2 undergoes microvibration at the PWM frequency to generate noise. Frequency of the noise is equal to the PWM frequency and the step-out state is notified to a user by setting the PWM frequency as an audible frequency for human being so that the user can restart by user's own judgment. <P>COPYRIGHT: (C)2005,JPO&NCIPI |
