摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply device that controls a rectifying current generated by a synchronous rectifier arranged at the secondary side of a transformer not to flow back, and can reduce a loss induced to the rectifier. SOLUTION: A pair of switching elements Q1, Q2 are connected in series to a DC power supply Vi, and the middle point of the connection is connected to the primary winding N1 of the transformer T1, and voltages induced from the primary winding N1 of the transformer T1 to the secondary winding N2 thereof are synchronously rectified by the synchronous rectifier Q3, Q4, to obtain output voltages Vo. Here, on the basis of a resonant current generated at the primary winding N1 of the transformer T1, a voltage generated at an auxiliary winding N4 of the transformer T1, and an on-period with respect to either of the switching elements Q1, Q2, control signals VQ3gs, VQ4gs that control the synchronous rectifier Q3 , Q4 to be turned on and off so that the control signals are shorter than on-control periods of the switching elements. COPYRIGHT: (C)2005,JPO&NCIPI
|