Patent ID: 7466568

Claim:
A self-excited switching power supply circuit, comprising: a transformer including a main winding and an auxiliary winding, which are magnetically coupled together on a primary winding side; a switching element for intermittently supplying a direct-current voltage to the main winding; and a controller for turning ON/OFF the switching element using a voltage induced across the auxiliary winding by the intermittent supply of the direct-current voltage, wherein the switching power supply circuit includes a startup circuit, the startup circuit including: a startup switch connected to the main winding; and a driving pulse generator for outputting a driving pulse to the startup switch for turning ON the startup switch, wherein as the startup switch is turned ON by the driving pulse output from the driving pulse generator, a current flows through the main winding connected to the startup switch, thereby generating an induced voltage across the auxiliary winding, which turns ON/OFF the switching element.