SYNCHRONOUS RECTIFICATION SWITCHING POWER SUPPLY

摘要

PROBLEM TO BE SOLVED: To provide a flyback-type synchronous rectification power supply wherein an element for rectification is turned off without fail before a main switch is turned on even if the on-duration of a main switching element is lengthened due to a sudden change in a load. SOLUTION: The primary winding N1 of a transformer T and the main switch element Q1 are connected in series between input terminals. The element Q2 for rectification connected in series with the secondary winding of the transformer T is provided between output terminals. A driving means comprising an auxiliary winding N3 and the like is provided which turns on the element Q2 for rectification complementarily with the main switch element Q1. A transistor Tr1 which is an interrupting means for turning off the element Q2 for rectification is provided between the gate and source of the element Q2 for rectification. Timing with which an interrupting means turns off the element Q2 for rectification is set as a time which is a certain time after the main switch element Q1 is turned on and is within a range close to the certain cycle of driving the main switch element Q1 as much as possible. COPYRIGHT: (C)2004,JPO