Patent ID: 8716988

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 multiplier that carries out a multiplication of a voltage error 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; and at least one circuit of a current peak waveform generator circuit that generates a current peak waveform signal of a waveform tracking a peak value of the inductor current signal, or a waveform similar to the tracking waveform, and a soft-stop overvoltage detection voltage generator circuit that generates a soft-stop overvoltage detection voltage proportional to the output voltage, wherein the output of the multiplier is reduced in accordance with the current peak waveform signal when the current peak waveform signal exceeds a first threshold value, or the output of the multiplier is reduced in accordance with the soft-stop overvoltage detection voltage when the soft-stop overvoltage detection voltage exceeds a second threshold value; an overcurrent protection circuit that, a third threshold value higher than the first threshold value being set, detects that the inductor current signal has exceeded the third threshold value, and outputs an overcurrent detection signal, wherein the switching element is turned off by the overcurrent detection signal; wherein a fifth threshold value higher than the first threshold value and lower than the third threshold value is further set in the overcurrent protection circuit and, on the inductor current signal exceeding the third threshold value and the overcurrent detection signal being output, the overcurrent detection signal continues to be output until the overcurrent detection signal reaches the fifth threshold value.