Patent ID: 9541928
Date: 2017-01-10
CPC Classifications: G05F,H02M

Claim:
1. A power supply device comprising: an output transistor that is turned on and off to generate an output voltage from an input voltage; a feedback voltage generation portion that generates a feedback voltage corresponding to the output voltage; a soft start voltage generation portion that generates a soft start voltage which gently increases when the power supply device is started up; an error amplifier that generates an error voltage corresponding to a difference between the feedback voltage and the lower of a predetermined reference voltage and the soft start voltage; an oscillator that generates a clock signal of a predetermined frequency; a slope voltage generation portion that generates a slope voltage in synchronization with the clock signal; a comparator that compares the error voltage and the slope voltage to generate a comparison signal; a PWM pulse generation portion that generates a PWM pulse based on the clock signal and the comparison signal; an on-time fixed pulse generation portion that uses the comparison signal as a trigger to generate an on-time fixed pulse where an on-time and an on-time number are constant; a one shot pulse generation portion that generates once, when the soft start voltage exceeds a predetermined threshold voltage, a one shot pulse where the on-time and the on-time number are constant; a selector that selects any one of the PWM pulse, the on-time fixed pulse and the one shot pulse to output the selected one as a pulse signal; and a driver that turns on and off the output transistor according to a logic level of the pulse signal output from the selector, wherein the selector selects the PWM pulse when the power supply device is started up, and selects the one shot pulse when the soft start voltage exceeds the threshold voltage.