Abstract: A power supply device has an error amplifier producing an error voltage by amplifying a difference between a feedback voltage according to an output voltage and a predetermined reference voltage, an output portion producing a desired output voltage from an input voltage in such a way that the error voltage is reduced, and a clamping portion setting, during a predetermined period after startup of the power supply device, an upper limit of the error voltage to a value that is lower than a value obtained at normal times, such that the lower the input voltage the higher the upper limit, the higher the input voltage the lower the upper limit.

Abstract: A drive unit has a load driving portion driving a load by a PWM drive method; a soft-start function portion for achieving a soft-start function; and a soft-start disabling portion counting a time elapsed after a PWM signal is turned on at start-up of the unit, and disabling the soft-start function when a count value reaches a predetermined value.

Abstract: A step-up switching power supply device with synchronous rectification includes a first switch that is turned on at startup of the device and a second switch that is turned on when an output voltage reaches an input voltage, the first and seconds switches being connected in parallel between the back gate and the source of a synchronous rectifier transistor.