Patent ID: 8379419

Claim:
A power factor correction type switching power supply unit that, based on an alternating current input voltage full-wave rectified in a diode bridge, supplies a direct current output voltage of a step-up type converter having an inductor, a switching element, and an output capacitor to a load, the unit comprising: a voltage error amplifier circuit that amplifies a difference between a detected value of the direct current output voltage and a first reference voltage, and outputs a voltage error signal; a multiplier that multiplies the voltage error signal output from the voltage error amplifier circuit 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 signal of the multiplier and an inductor current signal detecting an inductor current flowing through the inductor; a soft-stop overvoltage protection circuit, into which a soft-stop overvoltage detection voltage corresponding to the detected value of the direct current output voltage is input, that reduces the output of the multiplier in accordance with the soft-stop overvoltage detection voltage when the soft-stop overvoltage detection voltage exceeds a first threshold value; an overvoltage protection circuit that, a second threshold value higher than the first threshold value being set, compulsorily turns off the switching element by outputting an overvoltage detection signal when the soft-stop overvoltage detection voltage exceeds the second threshold value; a transient response corrector circuit having an output increase circuit that, a second reference voltage lower than the first reference voltage being set, compulsorily increases the output of the voltage error amplifier circuit when the detected value of the direct current output voltage is equal to or lower than the second reference voltage; and an input voltage monitoring circuit that monitors the detected value of the full-wave rectified alternating current input voltage using a third reference voltage, permits the operation of the transient response corrector circuit provided that the detected value of the full-wave rectified alternating current input voltage does not exceed the third reference voltage during a half-cycle of the alternating current input voltage, and prohibits the operation of the transient response corrector circuit when the detected value exceeds the third reference voltage.