SWITCHING POWER SUPPLY CIRCUIT AND CONTROL METHOD THEREFOR

摘要

A switching power supply circuit includes a PWM drive circuit (12) that performs the PWM driving of a switching element (Q1) at a duty ratio (D) commensurate with an input target voltage (VS), and generates from an input voltage (VB) an output voltage (VTL) whose target value is the target voltage (VS), by the PWM drive circuit (12) driving the switching element (Q1). The switching power supply circuit further includes a control circuit (13) and a target voltage limiting circuit (14) that together fix the duty ratio (D) regardless of the target voltage (VS), when a difference between the input voltage (VB) and the target voltage (VS) is less than or equal to a predetermined constant value (a).