Patent ID: 7209335

Claim:
A switching power supply apparatus including: a switching device, having one end thereof connected to an input terminal to which a direct-current voltage is fed, for switching and thereby converting the direct-current voltage into a pulsating voltage; a coil, connected between another end of the switching device and an output terminal, for smoothing and thereby converting the pulsating voltage into a direct-current voltage different from the direct-current voltage; an output capacitor, connected between the output terminal and ground, for smoothing the direct-current voltage from the coil and thereby producing an output voltage; and a rectifying device, connected between a node at which the switching device and the coil are connected together and ground, for permitting a current to flow through the coil during an off-state period of the switching device, wherein the switching power supply apparatus comprises: a current detection portion that outputs a detection signal that varies in proportion to a current that flows, while increasing with time, through the switching device during an on-state period of the switching device; a comparison portion that compares an error signal indicating a difference of a feedback signal obtained by dividing the output voltage from a reference voltage with the detection signal; a switching control portion that turns the switching device on according to a pulse signal from an oscillation portion and that turns the switching device off according to an output obtained from the comparison portion when the detection signal becomes greater than the error signal; an overcurrent detection portion that detects an overcurrent in the current flowing through the switching device by comparing the detection signal with a predetermined threshold value and that, on detection of an overcurrent, turns the switching device off; a first current compensation portion that superimposes a first current compensation signal on the detection signal fed to the comparing portion to produce a first current-compensated signal; and a second current compensation portion that superimposes a second current compensation signal on the detection signal fed to the overcurrent detection portion to produce a second current-compensated signal, wherein a variation in the current flowing through the switching device is made to converge as a result of slopes of the first and second current-compensated signals being steeper than a slope of a line connecting together the values of the detection signal as observed when the switching device turns from on to off and when the switching device turns from off back to on.