| 摘要 |
A circuit and method measures the voltage at the main motor winding (1) and detects the points in the electromagnetic wave cycle at which this voltage "crosses" zero. The method and circuit also measures the voltage at the auxiliary motor winding (2). The voltages measured in the main winding (1) a nd in the auxiliary winding (2) are compared by the circuit (13) as a means for starting and restarting the auxiliary winding (2). The circuit and method al so detects the points in the electromagnetic wave cycle where the current in th e auxiliary winding "crosses" zero and compares the phase of these current zer o crossing points with a window pulse (11) that is generated when the main voltage crosses zero. When the zero current crossing points fall within the window pulse, the auxiliary winding (2) is up to proper operating speed and the auxiliary winding (2) is disconnected by the starting circuit. If the lo ad on the main motor winding (1) increases or the main motor winding (1) speed decreases below a certain predetermined speed, the auxiliary winding (2) is switched back into the circuit to boost the speed of the main motor winding (1).
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