| 摘要 |
An power supply circuit ( 2 ) includes a bridge rectifier circuit ( 22 ); a control circuit ( 23 ) having a switch circuit ( 231 ) and a pulse width modulation circuit ( 232 ); a high frequency transformer ( 24 ); at least one commutating and filter circuit ( 25 ); and a positive feedback circuit ( 29 ). An alternating current voltage input from an external source is converted into a high frequency direct current voltage via the bridge rectifier circuit, and the high frequency DC voltage is outputted from the power supply circuit via the switch circuit, the high frequency transformer, and the at least one commutating and filter circuit. The positive feedback circuit receives the high frequency DC voltage outputted by the bridge rectifier circuit and transmits the high frequency DC voltage to the pulse width modulation circuit, and the pulse width modulation circuit controls a conduction time of the switch circuit according to the received high frequency DC voltage.
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