Patent ID: 8194417

Claim:
A two-stage switching power supply for receiving an input voltage and generating an output voltage, said two-stage switching power supply comprising: a first-stage power circuit connected to a power bus for receiving an input voltage, and comprising a first switching circuit, wherein said input voltage is converted into a bus voltage by conducting or shutting off said first switching circuit; a second-stage power circuit connected to said power bus for receiving said bus voltage, and comprising a second switching circuit, wherein said bus voltage is converted into said output voltage by conducting or shutting off said second switching circuit; an output detecting circuit connected to said second-stage power circuit and generating an output detecting signal according to said output voltage and/or an output current; and a power control unit connected to a control terminal of said first switching circuit of said first-stage power circuit and a control terminal of said second switching circuit of said second-stage power circuit for controlling operations of said first switching circuit and said second switching circuit according to said output detecting signal, wherein a first-stage voltage gain value of said first-stage power circuit and a second-stage voltage gain value of said second-stage power circuit are altered as said output detecting signal is changed, so that said output voltage or said output current is maintained at a rated value, wherein said bus voltage is dynamically adjusted according to said output detecting signal.