Abstract: A digitally controlled switched-mode voltage converter having conversion circuit (CMS) including a switching device (SW) for the purpose of converting an input voltage (U.sub.i) into an output voltage (U.sub.o); and a control device (CM) for controlling a duty cycle of the switching device (SM) in steps having discrete values (D.sub.c1,D.sub.c2). The control device (CM) include a change-over device (SO) for continually switching the duty cycle between at least two discrete values (D.sub.c1,D.sub.c2) in such a manner that the average value of the duty cycle corresponds to a target duty cycle (T.sub.dc).

Abstract: A power supply comprising a coil a switching transistor for establishing a conduction path between the input terminal and the coil during an on-time and for interrupting the conduction path between the input terminal and the coil during an off-time. A diode is provided for sustaining a conduction path for the current through the coil (20) upon interruption of the conduction path between the input terminal (20) and the coil and an apparatus is provided for varying the ratio between the on-time and the off-time of the switching transistor in response to a difference between an output voltage across the load and a first reference voltage (VI). The power supply exhibits an improved efficiency by maintaining the ratio constant if the output voltage lies between two reference values. Within this voltage window defined by the two reference values the power supply is self-regulating, as a result of which the control may be disabled so that the efficiency is improved.