Patent ID: 8692531

Claim:
A switching regulator for converting an input voltage to a desired output voltage by controlling turning ON and OFF of switching elements with a pulse width modulation signal, the switching regulator comprising: a communication interface circuit that receives external operation instructions; an AD conversion circuit that converts an error voltage into a digital error signal, the error voltage being a difference between a reference voltage and a detected output voltage that is obtained by dividing the output voltage with a dividing proportion determined by an output voltage setting section; a controller that calculates a duty factor signal for determining an ON time proportion of the switching elements by digital operation based on the digital error signal; and a digital PWM circuit that generates the pulse width modulation signal corresponding to the duty factor signal; wherein the dividing proportion determined in the output voltage setting section is changed according to output voltage changing instruction from the communication interface circuit; and the controller comprises an output voltage changing control section that performs operations: to stop digital operation using the digital error signal upon receiving the output voltage changing instruction; to calculate a fixed duty factor, which is the duty factor giving a changing time output voltage for a steady state from a changing time input voltage; to assign the fixed duty factor to an initial value of the duty factor signal after a changing time; to determine compensation coefficients for use in digital operation appropriate for the output voltage setting value; and to control changing operation on the output voltage setting section.