SWITCHING POWER SUPPLY

PROBLEM TO BE SOLVED: To provide a switching power supply free from thermal destruction even if the short-circuit state of a load is continued for a long period of time, when an input voltage from a commercial power source is high. SOLUTION: When the load connected between a positive output terminal 10 and a negative one 11 is short-circuited, this short-circuit state is detected by an output voltage detecting circuit 12 and a switching control circuit stops its operation. At a start-up, a current from a bridge rectifier circuit 4 is supplied as a starting current to the switching control circuit 14 via a constant current circuit 21. Thus, even if an AC voltage of the commercial power source becomes higher, a constant current flows in the switching control circuit 14 so that, in the load short-circuit state, power consumption on the higher input voltage from the commercial power source can be reduced to a level close to that on a lower input voltage. COPYRIGHT: (C)2004,JPO