Patent ID: 7315153
Filing Date: 2008-01-01
Classification: H02M,Y02B

Abstract:
1. A switching power supply device, comprising: an inductor, wherein an input of said inductor is connected to a connecting point of the inductor; a switch element which controls a current that flows through the inductor, said switch element being connected between an input voltage and said connecting point of the inductor; a clamp element which clamps a back electromotive voltage generated across the inductor to a predetermined potential when the switch element is in an off state, said clamp element being connected between said connecting point of the inductor and an output of said inductor; a series circuit provided in a parallel configuration with the inductor and comprising a resistive element and a capacitive element, said series circuit being connected between said connecting point of the inductor and said output of the inductor; and a voltage comparator having first and second threshold voltages which are different from each other, wherein the current supply side of the switch element is supplied with the input voltage, a load circuit is supplied with a load current from the output of the inductor, and discrimination is made, by said voltage comparator, between a voltage obtained from a connecting point, between the resistive element and the capacitive element, of the series circuit and each of the first and second threshold voltages, wherein results of the discrimination between the voltage obtained from the connecting point of the series circuit and each of the first and second threshold voltages are used to control the switch element and to regulate the voltage obtained from the connecting point of the series circuit to be equal to the first threshold voltage, thereby varying the current flowing through the inductor in accordance with a variation in the load current; and wherein said switching power supply device is provided with an external sync input control circuit which has a sync terminal input with a synchronizing signal for periodically bringing the switch element to an on state when a frequency of conducting the discrimination performed by the voltage comparator is less than or equal to a predetermined frequency.