Patent ID: 8421430

Claim:
A digital control switching power supply unit that converts an input voltage into a desired output voltage using a pulse width modulation signal, comprising: an analog-to-digital converter circuit that includes: a delay line circuit that has a first delay element array wherein delay elements whose delay times are controlled by a bias current are connected in series, and that converts a current value of the bias current flowing through the delay elements of the first delay element array into a digital value using a delay time of a start signal transmitted through the first delay element array; a phase difference detector circuit that detects a phase difference between a switching cycle fixed by the pulse width modulation signal and a cycle of an analog-to-digital conversion wherein the delay line circuit converts the current value of the bias current into the digital value; a charge pump circuit that generates a bias control voltage for generating the bias current in accordance with an output of the phase difference detector circuit; and a bias current indicator circuit that determines the bias current based on an output of the charge pump circuit, and on a result of a comparison of a detected value of the output voltage and a reference voltage.