Patent ID: 9564819
Date: 2017-02-07
CPC Classifications: H02M,Y02B

Claim:
1. A switching power supply device, comprising: a main transformer that has a primary-side main winding and a secondary-side main winding; a first main switch that is connected between a high potential terminal of an input direct current voltage source and the primary-side main winding; a second main switch that is connected between a low potential terminal of the input direct current voltage source and the primary-side main winding; a control circuit configured to output a driving pulse signal from a driving pulse signal output terminal that is configured to synchronize the first and second main switches to perform an ON and OFF driving operation; a first rectifying device having a first cathode and a first anode, the first cathode being connected to a first node connected between the first main switch and the primary-side main winding, the first anode being connected to the low potential terminal of the input direct current voltage source; a second rectifying device having a second cathode and a second anode, the second anode being connected to a second node connected between the second main switch and the primary-side main winding, the second cathode being connected to the high potential terminal of the input direct current voltage source; a synchronous rectifier circuit; and a positive bias circuit configured to apply a positive bias to a control terminal of one of the first and second main switches so as to turn the one of the first and second main switches ON, wherein when the first and second main switches stop a switching operation while an output voltage exists between output terminals, the positive bias circuit applies the positive bias to only the one of the first and second main switches.