| 摘要 |
A switching power supply is provided which is capable of preventing abnormal operation of a synchronous rectifier circuit thereof, which is caused by a discontinuous current mode, and capable of enhancing an input power factor thereof. A transformer has a primary winding and a secondary winding. A first switching element is connected in series with the primary winding of the transformer, for switching an input voltage. A diode rectifies an induced voltage induced in the secondary winding of the transformer to generate a rectified current. A control signal is generated which has a current value or a voltage value approximately proportional to a current value of the rectified current. A second switching element is connected in parallel with the diode in an equivalent fashion and has a control terminal to which the control signal is input. The second switching element operates in response to the control signal for rectifying the induced voltage. A current is prevented from flowing into the primary winding during an OFF period of the first switching element.
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