Patent ID: 8903263

Claim:
A switching power supply device which comprises: a switching element configured to switch an input voltage; a rectifying circuit including an inductor and a first rectifying element which are connected to the switching element, and configured to rectify the voltage switched by the switching element; a control circuit configured to control a switching state of the switching element such that a voltage rectified by the rectifying circuit is close to a predetermined target value in accordance with the output of the rectifying circuit; an overload protection circuit connected to the inductor and the first rectifying element, wherein the overload protection circuit is configured to convert a current flowing through the first rectifying element into a voltage and output the converted voltage, and is further configured to reduce an on-time of the switching element to reduce an output from the rectifying circuit; a detection circuit constructed to detect a value corresponding to a current flowing through the first rectifying element; and an averaging unit constructed to average the detection result of said detection circuit, wherein the value corresponding to the current detected by the detection circuit is an output of said averaging unit, wherein a first terminal of the inductor and a first terminal of the first rectifying element are connected to a first terminal of the switching element, wherein a first output terminal used to connect a load and a first terminal of a capacitor are connected to a second terminal of the inductor, wherein a first terminal of a detection resistor serving as said detection circuit is connected to a second terminal of the first rectifying element, wherein a second terminal of the capacitor and a second terminal used to connect a load are connected to a second terminal of the detection resistor, wherein said averaging unit comprises an averaging resistor and an averaging capacitor, wherein the second terminal of the first rectifying element and a first terminal of the detection resistor are connected to a first terminal of the averaging resistor, and wherein a second terminal of the averaging resistor is connected to a first terminal of the averaging capacitor, and the second terminal of the detection resistor is connected to a second terminal of the capacitor.