Patent ID: 8643302

Claim:
A switching power-supply device comprising: a first inductor; a switching element configured to supply, when the switching element is on, a power-supply voltage of a direct-current power supply to and feed an electric current to the first inductor; a constant current element connected to the switching element in series and configured to turn off the switching element when the electric current of the switching element exceeds a predetermined current value; a rectifying element connected to any one of the switching element and the constant current element in series and configured to feed the electric current of the first inductor when the switching element is turned off; a second inductor magnetically coupled to the first inductor and configured to have induced therein potential for turning on the switching element when the electric current of the first inductor increases and have induced therein potential for turning off the switching element when the electric current of the first inductor decreases and supply the induced potential to a control terminal of the switching element; and a constant voltage circuit configured to apply control potential to a control terminal of the constant current element.