Switching power supply unit and semiconductor device for switching power supply

摘要

A control circuit for controlling an operation of a switching device includes: an output load detection circuit for receiving a feedback signal from a feedback circuit; an error amplification circuit for producing an error voltage signal based on an output signal from the output load detection circuit and a reference voltage; a drain current detection circuit for detecting a drain current; and a light load detection circuit for stopping a switching operation when the error voltage signal is lower than a lower limit voltage value while resuming the switching operation when the error voltage signal is higher than an upper limit voltage value. The reference voltage output from a reference voltage source of the light load detection circuit is selected from the lower limit voltage value and the upper limit voltage value based on the value of an output voltage from a comparator.