| 摘要 |
PROBLEM TO BE SOLVED: To provide an AC-DC converter capable of suppressing the loss incident to rectification operation regardless of the load, by switching the control between synchronous rectification system and asynchronous rectification system depending on the load.SOLUTION: An AC-DC converter 1a includes a synchronous rectification control circuit 2a having a bridge control circuit 3a and a synchronous rectification mask circuit 4a, and a rectification bridge 6. The synchronous rectification mask circuit 4a determines the differential voltage VD1 between a rectification voltage VO1 when the AC voltages VAC1 and VAC2 go above the rectification voltage VO1, and a terminal voltage VC1, and outputs a high level mask signal MA1 when the differential voltage VD1 is equal to or larger than a reference voltage VREF1. Since the PMOS transistors TP1-TP4 of the rectification bridge 6 are maintained in off state by the high level mask signal MA1, the bridge control circuit 3a does not perform synchronous rectification, thereby suppressing gate drive loss incident to rectification operation. |
