| 摘要 |
A power factor correction type switching power supply unit can change reference values of an overcurrent limit at an optimum timing at a time of an overcurrent protection of a step-up type converter, so that no sudden change occurs in an inductor current. A detection level selection circuit selects one of first and second threshold values with a selection signal, and outputs it as an overcurrent detection level to an overcurrent detection circuit. An input voltage monitoring circuit determines the selection signal in such a way that the larger of two threshold values is selected when an alternating current input voltage exceeds a first reference voltage, and the smaller threshold value is selected when the alternating current input voltage does not exceed a second reference voltage, and outputs the selection signal to the detection level selection circuit at a timing at which the alternating current input voltage approaches a zero. |
