Patent ID: 7859864

Claim:
A switching power supply device, comprising: a DC power supply; a transformer having primary windings, and supplying power to a load at a secondary side of the transformer according to a setting voltage; a switching element connected in series to the primary windings of the transformer; a feedback circuit connected to the secondary side and outputting to the primary side of the transformer a feedback signal obtained by amplifying a difference between the setting voltage and a voltage output to the load; a switching power supply control device for performing on/off control of the switching element based on the feedback signal; a current detection device for detecting a value of current flowing in the switching element as a voltage signal with polarity, said current detection device detecting a voltage relative to a reference potential of the switching power supply control device such that as the current value increases, the voltage relative to the reference potential is reduced; and a correction circuit attached to the switching power supply control device, said correction circuit acting only during on intervals of the switching element, and applying a positive offset voltage to the voltage signal output from the current detection device.