Patent ID: 9429963
Filing Date: 2016-08-30
CPC Classification: G05F,H02M

Claim Text:
1. A power supply device comprising: an output transistor operable to be turned on and off to generate an output voltage from an input voltage; a feedback voltage generation portion operable to generate a feedback voltage corresponding to the out voltage; an error amplifier operable to generate an error voltage corresponding to a difference between a predetermined reference voltage and the feedback voltage; an oscillator operable to generate a clock signal of a predetermined frequency; a slope voltage generation portion operable to generate a slope voltage in synchronization with the clock signal; a comparator operable to compare the error voltage and the slope voltage to generate a comparison signal; a PWM pulse generation portion operable to generate a PWM pulse based on the clock signal and the comparison signal; an on-time fixed pulse generation portion operable to use 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 selector operable to select any one of the PWM pulse and the on-time fixed pulse; a driver operable to turn on and off the output transistor according to an output of the selector; and a selector control portion operable to generate a control signal of the selector such that any one of the PWM pulse and the on-time fixed pulse is selected according to whether or not the comparison signal is kept at a same logic level over a predetermined mask period wherein a second threshold current when an on-time fixed mode where the on-time fixed pulse is selected is switched to a PWM mode where the PWM pulse is selected is determined by charge that is supplied to a load each time the output transistor is turned on N times in the on-time fixed mode and an on-time of each of the on-time fixed pulses, and wherein the second threshold current is expressed by N×Q/Tmask, where N is an on-time number of the on-time fixed pulse, Q is charge that is supplied to the load each time the output transistor is turned on and Tmask is the mask period.