Patent ID: 6914789

Claim:
A switching power supply apparatus comprising a switching element, a control circuit for controlling a switching operation of the switching element, a transformer for converting an inputted first DC voltage into an AC electric power by means of the switching operation of the switching element and outputting the AC electric power, an output voltage generating circuit for generating a second DC voltage from the AC electric power and outputting the voltage to an external load, and a power supply circuit for generating a DC voltage corresponding to the second DC voltage and setting the generated DC voltage as a power supply voltage of the control circuit, wherein said control circuit comprising: an oscillator for generating a switching signal that induces a switching operation in the switching element, an element current detecting circuit for detecting element current that flows through the switching element and outputting the current as an element current detecting signal, an error amplifier for generating and outputting an error voltage signal as a voltage value that corresponds to a difference between a reference voltage and the power supply voltage, an element current detecting comparator for comparing the voltage value of the error voltage signal and that of the element current detecting signal, and outputting a comparison signal that corresponds to a comparison result thereof, a switching signal control circuit for controlling the switching signal so that the second DC voltage is brought to a prescribed voltage on a basis of the comparison signal from the element current detecting comparator, and outputting this as a control signal to the switching element, and an on-blanking pulse generating circuit for generating a blanking pulse signal that disables, based on the voltage value of the error voltage signal, the comparison signal from the element current detecting comparator for a period corresponding to a load condition starting from a moment when the switching element is turned on, and ensuring that the switching element is not turned off during the period.