Switching power supply device for suppressing an increase in ripple output voltage

摘要

An apparatus is provided to suppress an increase in the ripple voltage inevitable in a conventional switching power supply device used at low temperatures. A switching power supply device is provided that has a DC—DC converter that receives an input voltage and outputs a varying voltage by varying the ratio of on periods to off periods of a switching transistor. An error amplifier compares the output voltage of the DC—DC converter or a divided voltage thereof with a reference voltage and outputs an error voltage. An operator produces a pulse signal according to the error voltage and controls the switching transistor with the pulse signal. A gain control circuit varies the gain of the error amplifier according to at least one of the duty factor of the pulse signal and the ambient temperature.