Patent ID: 8384324
Filing Date: 2013-02-26
Classification: H02P

Abstract:
1. A motor drive circuit configured to drive a motor based on first and second position detection signals opposite in phase to each other, the signals having a frequency corresponding to a rotational speed of the motor and indicating a rotational position of the motor, the circuit comprising: a first level-shift circuit configured to shift a level of at least either one of the first and second position detection signals so that a period, during which a first output signal corresponding to the first position detection signal is higher in level than a second output signal corresponding to the second position detection signal, becomes longer than a period, during which the second output signal is higher in level than the first output signal; a second level-shift circuit configured to shift a level of at least either one of the first and second position detection signals so that a period, during which a third output signal corresponding to the first position detection signal is higher in level than a fourth output signal corresponding to the second position detection signal, becomes shorter than a period, during which the fourth output signal is higher in level than the third output signal; a timing detecting circuit configured to detect first timing at which the first and second output signals cross in level, and second timing at which the third and fourth output signals cross in level; and an output circuit configured to output, to a drive circuit configured to drive a coil of the motor, an instruction signal for changing a drive current of the coil in a gradual manner only during a period between the first timing and the second timing, the period including a third timing at which the first and second position detection signals cross in level.