Patent ID: 8803488

Claim:
A power supply apparatus comprising: a switching element which is connected to an input terminal and performs switching driving; a rectifying element; a reactor which smoothes an input voltage transformed by said switching element and said rectifying element; a smoothing capacitor which smoothes the output of said reactor; a current detector which detects an output current; and a switching control unit which calculates a duty ratio of said switching element by an output voltage and a target voltage, calculates switching frequency from a load state to be determined by the current detected by said current detector, and controls said switching element, the calculation of the switching frequency being performed by the current detected by said current detector so that the switching frequency is set to be low if the current is large and the switching frequency is set to be high if the current is small, wherein the switching frequency is set to be high if the input voltage is high and the switching frequency is set to be low if the input voltage is low depending on the input voltage inputted to said input terminal, and said switching element is controlled by restricting the switching frequency so that the switching frequency to be set by the current detected by said current detector is not lower than the switching frequency to be set by the input voltage.