| 摘要 |
PROBLEM TO BE SOLVED: To avoid detection of zero crossing at a position different from a practical one by switching a PWM mode over to LINEA, only at the time when switchover of an electromotive force is detected. SOLUTION: A PWM drive mode is set at the time of the start-up of a brushless DC mode 2, and the procedure thereof is executed by a start-up circuit 38. In PWMTIME, the switchover from the PWM mode to an LINEA mode is enabled during the period when the PWM mode is enabled. During a masking period, a detecting circuit 35 is disabled, so as to mask off switching noise in the change from the PWM mode to the LINEA mode. The switchover from the PWM mode to the LINEA mode is outputted from the detecting circuit 35 and set by a rise of a signal TOFFEN. When MASK is ended, on the other hand, the detecting circuit 35 is enabled. As a result, the PWM mode is enabled again. |
