Patent ID: 8310795

Claim:
A power factor correction type switching power supply unit that enables an overcurrent limit value to be changed to at least two differing magnitudes in accordance with the size of a full-wave rectified alternating current input voltage to a step-up type converter having an inductor, a switching element, and an output capacitor, the unit comprising: a multiplier that multiplies a voltage error amplification signal, wherein the difference between a detected value of an output voltage and a reference voltage is amplified, and a detected value of the full-wave rectified alternating current input voltage; a control circuit that on-off controls the switching element based on an output of the multiplier and an inductor current signal detecting an inductor current flowing through the inductor; an overcurrent protection circuit that, by setting one of a first threshold value and second threshold value of mutually differing sizes, detects that the inductor current signal has exceeded the first threshold value or second threshold value, and generates an overcurrent detection signal limiting the inductor current; and an input voltage monitoring circuit that monitors the detected value of the full-wave rectified alternating current input voltage, selects one from first or second threshold in such a way that the threshold, whose absolute value is lower between first and second threshold, is selected and set when the detected value of the full-wave rectified alternating current input voltage exceeds a first reference voltage during a half-cycle of the alternating current input voltage, and the threshold, whose absolute value is higher between first and second threshold, is selected and set when a second reference voltage, which is a voltage equal to or lower than the first reference voltage, is not exceeded, inputs the selection signal into the overcurrent protection circuit, and carries out a change of the selection signal at a timing at which the alternating current input voltage reaches a zero level vicinity.