Patent ID: 7782638
Filing Date: 2010-08-24
Classification: H02M

Abstract:
1. A switching power supply device comprising: a transformer having a primary coil, a secondary coil, and an auxiliary coil; a switching device that switches to control a first DC voltage input to the primary coil; an output voltage generating unit operable to generate a second DC voltage as an output voltage by rectifying and smoothing the AC voltage generated in the secondary coil as a result of the switching operation of said switching device; a first external connection pin which is disposed to a control circuit operable to control the switching operation of said switching device, and to which is input the rectified and smoothed voltage level of the AC voltage of the auxiliary coil proportional to the secondary coil; a first detector operable to detect an overload when an energy supplied to said output voltage generating unit becomes greater than or equal to a first predetermined level; a second detector operable to have a maximum value set for the energy supplied to said output voltage generating unit, and to detect an overload when the voltage of said first external connection pin becomes less than or equal to a second predetermined level; a second external connection pin of which a voltage increases when an energy supplied to said output voltage generating unit becomes greater than or equal to a third predetermined level; a first overload protector operable to be applied when said first detector detects the overload; and a second overload protector operable to be applied when said second detector detects the overload, wherein said first detector detects the overload when the voltage of said second external connection pin increases to a fourth predetermined level which is above a normal operating voltage under which no overload is detected, and said second overload protector is made operative and said first overload protector is made inoperative by connecting said second external connection pin to a voltage clamping circuit operable to prevent the voltage of said second external connection pin from increasing to the fourth predetermined level.