Patent ID: 8149598

Claim:
A switching power supply apparatus, comprising: a transformer including a primary winding, a secondary winding, and an auxiliary winding; a switching device connected in series with said primary winding; an auxiliary power voltage circuit which is connected to said auxiliary winding and is configured to generate an auxiliary power voltage by using an alternating-current voltage induced in said auxiliary winding; and a control circuit configured to control an operation of said switching device, wherein said control circuit includes: a power source terminal through which the auxiliary power voltage is supplied; a difference device configured to generate a difference voltage depending on a difference between the auxiliary power voltage and a first reference voltage; a device current detection circuit configured to detect a device current flowing in said switching device, and to generate a device current detection signal indicating an amount of the device current; a drive circuit configured to generate a drive pulse signal having a duty cycle based on a difference between the difference voltage and the device current detection signal, and to drive said switching device by using the generated drive pulse signal; and a dummy load circuit through which a dummy load current flows from said power source terminal when the difference voltage becomes equal to or higher than a second reference voltage.