The digitally controlled dc-dc converter has the advantage of high reliability, high controllability and high flexibility. A new digital controller for the PWM and/or PFM controlled switching dc-dc converters is presented, which is versatile in general use such as the switching frequency from 20 kHz to 70 kHz, the hard-switching and soft-switching and so forth. As an example, we apply this controller to half-bridge type series resonant dc-dc converter with auxiliary switches, in which both PWM and PFM control modes are employed, and the output characteristics of the converter are discussed. As a result, the relationships among circuit parameters of the proposed digital controller, switching frequency of the dc-dc converter, oscillation frequency of the VCO as analog to digital signal converter are defined.