Semiconductor device for switching power supply and switching power supply device

A semiconductor device for a switching power supply, the device being configured to generate a driving signal for performing ON/OFF control of a switching element connected in series to a primary winding of a transformer for voltage conversion, the transformer including a secondary winding and an auxiliary winding, the semiconductor device comprising:

• a resonance monitor circuit that monitors a resonance state of the secondary winding of the transformer, based on a voltage of the auxiliary winding;
• a timer circuit that generates a period signal that determines a switching period of the switching element;
• a turn-on circuit that outputs a turn-on signal for turning on the switching element, based on the period signal and a signal from the resonance monitor circuit;
• a turn-off circuit that outputs a turn-off signal for turning off the switching element in response to detecting a current with a predetermined current value flowing through the switching element;
• and
• a jitter generation circuit that generates a first jitter signal for giving jitter to a period of the period signal and a second jitter signal for giving jitter to the predetermined current value at which the turn-off circuit outputs the turn-off signal,
• wherein the first jitter signal and the second jitter signal have a predetermined phase difference.