| 摘要 |
A switching mode power supply and method for generating a bias voltage is described. The bias voltage is generated by using a current source coupled to a primary coil of a transformer during the start-up of the switching mode power supply. The generation of the bias voltage through the current source is stopped at a second time, a delay time after a first time when the bias voltage becomes essentially equal to a reference voltage that is an operational voltage of a PWM controller. The switching operation of a main switch is started after the first time, when the bias voltage exceeded the operational voltage. In this interval the bias voltage is also generated by the secondary coil of the transformer.
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