| 摘要 |
A commutated brushless dc motor includes a detector which senses the zero crossings of the unenergized winding. A timing system includes a reference capacitor coupled to the detection unit and charged to a voltage proportional to zero crossing time. The voltage is compared to a capacitor charged from a constant current source. At a percentage level of the reference capacitor, a commutating pulse is applied to a winding commutating circuit. The incoming pulses drive a counter and actuates a programmed decoder which generates output signals for commutation of the windings and selection of the next unenergized winding. The detector is selectively connected to sense the induced voltage in the unenergized winding. To start the motor, a separate charging circuit creates initial pulses to energize the windings and accelerate the motor. At a given speed, the zero crossing circuit is enabled. An integrated circuit system has the zero crossing signals applied to a resettable counter which counts at a fixed rate between zero crossings. The count is latched and is proportional to the time between zero crossings. The counter signal and the latched signal are compared to generate the commutating pulse.
|
