Patent ID: 7450404

Claim:
A switching power supply, comprising: an auxiliary circuit, comprising: an auxiliary capacitor; and an auxiliary switch electrically connected to said auxiliary capacitor in series; a transformer having a primary side electrically connected to said auxiliary circuit in parallel and a secondary side; an auxiliary switch control circuit electrically connected to said auxiliary switch and said primary side of said transformer and fixing a turn-on time of said auxiliary switch; a main switch having a first terminal electrically connected to said primary side of said transformer, a second terminal and a control terminal; a zero-voltage switching (ZVS) detector electrically connected to said first and said control terminals of said main switch; a first and a second rectifying switches electrically connected to said secondary side of said transformer; and a filter circuit electrically connected to said second rectifying switch in parallel, wherein said turn-on time of said auxiliary switch is fixed such that a turn-off time of said main switch is also fixed so as to accomplish ZVS of said main switch.