Patent ID: 8207718
Filing Date: 2012-06-26
Classification: H02M

Abstract:
1. A switching power supply circuit, comprising: a transformer converting a direct-current (DC) voltage into a first DC voltage and a second DC voltage; a switching control circuit controlling current flowing on the transformer for generating a first DC voltage and a second DC voltage; a DC-DC converter; and a signal selecting circuit comprising a buck circuit and a logic circuit, the buck circuit transforming the first DC voltage into a predetermined DC voltage to decrease the first DC voltage; and the logic circuit comparing and selecting one of the decreased first DC voltage and the second DC voltage to the DC-DC converter; wherein the buck circuit comprises a transistor having a first terminal and a control terminal, a regulating diode electrically connected to the first terminal and the control terminal of the transistor for decreasing the first DC voltage, and a resistor electrically connected to the transistor, the regulating diode and a ground terminal, the DC-DC converter converts the decreased first DC voltage or the second DC voltage into a third DC voltage.