Semiconductor device for switching power supply and ac-dc convertor

Abstract

A semiconductor device for a switching power supply includes first and second external terminals, ON and OFF timing generation circuits, and a drive pulse generation circuit. To the first and second external terminals, a feedback voltage and a voltage induced in an auxiliary winding are input, respectively. The ON and OFF timing generation circuits respectively generate timing signals turning on and off a switching element based on the voltages. The drive pulse generation circuit generates a pulse signal based on these signals. The ON timing generation circuit includes: a bottom detection circuit detecting a lowest point of the voltage of the second external terminal; and a timer circuit, and operates in a PWM mode and a quasi-resonant mode in response to a timing of an output of the timer circuit being before a timing of an output of the bottom detection circuit and the reverse case, respectively.