Patent ID: 7321222

Claim:
A switching power supply apparatus, including: a switching device for performing an on/off operation; a control circuit for controlling on/off of the switching device; a coil, a level of a current flowing therethrough being controlled by the switching device; a capacitor that is connected to the coil and that performs rectification together with the coil; and an oscillator for outputting to the control circuit an oscillating signal at intervals of a fixed time period for turning the switching device on, wherein the switching power supply apparatus outputs an output voltage from a node at which the capacitor and the coil are connected together, the switching power supply apparatus comprising: a current detection portion for detecting a current value flowing through the coil, converting the detected current value into a voltage value, and then outputting the voltage value thus obtained as a current detection voltage; a voltage source for adding an offset voltage to the current detection voltage from the current detection portion; and a comparator for comparing the current detection voltage to which the offset voltage is added by the voltage source with a voltage commensurate with a difference between a voltage commensurate with the output voltage and a reference voltage, wherein, if the comparator finds a magnitude of the current detection voltage to which the offset voltage is added to be greater than the voltage commensurate with a difference between the voltage commensurate with the output voltage and the reference voltage, the oscillating signal from the oscillator is masked, and the switching device is turned off.