SWITCHING POWER SOURCE DEVICE

摘要

PURPOSE:To provide a switching power source device in which an overvoltage protection can be executed without using a photocoupler for a special purpose of protection against an overvoltage. CONSTITUTION:An overvoltage detector 40 for detecting that an output voltage V2 of a secondary side becomes a predetermined value or more, and a switch circuit 50 for forcibly emitting a light from a photodiode of a photocoupler 28 for constant-voltage controlling in response to a signal from the detector 40 are provided instead of an overvoltage protective circuit and a photocoupler therefore.