| 摘要 |
PURPOSE:To realize accurate switching between start and reverse start by judging the rotational state of motor by means of a signal based on the counter- electromotive force. CONSTITUTION:Output from a starting pattern generating circuit is fed to a phase exciting pulse generating circuit in order to drive a transistor thus rotating a three-phase motor. A rotation detecting circuit then makes decisions whether the motor is rotating and whether the motor is rotating normally or not and produces a start/reverse start switching signal. A constant charging circuit 29 performs charging operation depending on a Low or High output from a comparator selecting circuit (CS). A peak value is held in a peak value hold circuit 30 and then subjected to subtraction through a subtraction circuit 31 and the subtraction result is compared with a voltage reference 33 through a comparator (CP) 32. Consequently, the duty of the output from the CS can be detected. Since the duty is about 50% when a motor 22 is rotating normally, the voltage reference 33 is set such that the CP 32 is inverted. Switching is then made between start and reverse start depending on the output level from the CP 32. |
