Isolated synchronous rectification type DC / DC converter, synchronous rectification controller, power supply using the same, power adapter and electronic equipment

摘要

PROBLEM TO BE SOLVED: To prevent a synchronous rectification transistor from being erroneously turned on when starting a DC/DC converter.SOLUTION: A DC voltage Vgenerated at a secondary side of a DC/DC converter 200 is supplied to a VCC terminal. A pulse generator 304 is operated with the DC voltage of the VCC terminal as a power source and generates a pulse signal S1, based on a voltage between both terminals of a synchronous rectification transistor M2. A driver 306 is operated with the DC voltage of the VCC terminal as a power source and switches the synchronous rectification transistor M2 in accordance with the pulse signal S1. Based on a drain voltage Vof the synchronous rectification transistor M2, an auxiliary power supply circuit 310 generates an auxiliary power supply voltage V. An OFF fixing circuit 320 is operated by receiving the auxiliary power supply voltage V, and fixes the synchronous rectification transistor M2 in OFF.SELECTED DRAWING: Figure 3