Patent ID: 9270177
Filing Date: 2016-02-23
CPC Classification: H02M,Y02B

Claim Text:
1. A switching power-supply device configured to convert and output a first direct voltage supplied from an input power source to a second direct voltage by alternately turning on and off a first switching element connected to the input power source and a second switching element connected in series to the first switching element, the switching power-supply device comprising: a reference voltage generation unit that generates a ramp signal and generates a second reference voltage in which the ramp signal is superimposed with a first reference voltage; a comparison unit that compares a feedback voltage, which is obtained by resistance voltage dividing of the second direct voltage, with the second reference voltage and outputs an effective signal at a timing, at which the feedback voltage becomes lower than the second reference voltage; and a driving signal generation unit that receives the effective signal and then supplies a driving signal to a driving unit turning on the first switching element during a period, during which the driving signal is supplied, a signal output unit that outputs a signal depending on a ratio between a period, during which the first switching element is turned on, and a period, during which the second switching element is turned on, wherein the driving signal generation unit controls the period of supplying the driving signal to the driving unit, depending on an input-and-output condition, wherein the reference voltage generation unit starts rising of the ramp signal during a period from a time point, at which the first switching element has been turned from on to off in response to the driving signal, to when the first switching element is turned on, wherein based on the signal, the driving signal generation unit shortens the period of supplying the driving signal as the ratio of the on-period of the second switching element to the on-period of the first switching element is increased, and wherein based on the signal, the reference voltage generation unit causes a slope of the ramp signal to become gentle as the ratio of the on-period of the second switching element to the on-period of the first switching element is increased.