SYNCHRONOUS RECTIFYING CONVERTER

摘要

PROBLEM TO BE SOLVED: To suppress an increase in reset voltage peak of an output transformer due to a self-oscillation phenomenon that occurs in a sudden change of an input, in a switching power supply of a synchronous rectifying circuit type, and prevent breakage of the power supply. SOLUTION: A synchronous rectifying-type converter converts a direct-current input voltage into a rectangular-wave pulse voltage through a switching element and applies the voltage to a primary winding of the output transformer and synchronously rectifies the output of the output transformer on a secondary winding side. The converter is provided with a circuit 29 for detecting the self-oscillation of a synchronous rectification circuit. The self-oscillation detection circuit 29 detects any asynchronousness in control signals from a control circuit 28 and voltage signals from the output transformer, and uses it as a self-oscillation detection signal. An auxiliary switch is installed in parallel between the gate and source of a synchronous rectification FET4 or a communication FET5 so that the gate and source of the synchronous rectification FET4 or the commutation FET5 are short-circuited or opened through the auxiliary switch by the self-oscillation detection signal.