Power supply device, and vehicle-mounted apparatus and vehicle using same

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.