Patent ID: 7453243

Claim:
A switching power supply device comprising: an oscillation circuit that generates an oscillation signal to switch a current flowing through a primary coil of a transformer; an oscillation control circuit that controls the oscillation signal of the oscillation circuit on a basis of a voltage induced to a secondary coil of the transformer such that a DC voltage becomes a predetermined value; a first power supply voltage generating circuit that generates a first DC power supply voltage by an output voltage of the secondary coil of the transformer; a second power supply voltage generating circuit that generates a second DC power supply voltage lower than the first DC power supply voltage by the output voltage of the secondary coil of the transformer; and a power supply feedback circuit that detects a variation of the second power supply voltage as an error signal by comparing a reference voltage generated on a basis of the first DC power supply voltage with the second DC power supply voltage, and supplies the error signal to the oscillation control circuit as a feedback signal, wherein a duty ratio and a frequency of an intermittent oscillation pulse are varied to determine the duty ratio and the frequency of the intermittent oscillation pulse that provides a lowest power consumption in a standby state and a microcomputer is configured to output the intermittent oscillation pulse with the determined duty ratio and frequency, the intermittent oscillation pulse output from the microcomputer is supplied to a connection point between a reference voltage line in the power supply feedback circuit and a control line of an error detecting element through a series circuit including a capacitor and a resistor, and the intermittent oscillation pulse with the determined duty ratio and frequency output from the microcomputer is supplied to the connection point through the series circuit including the capacitor and the resistor in the standby state.