Patent ID: 7778055

Claim:
An apparatus comprising: a voltage converter for supplying voltage to an electrical load, the voltage converter being electrically connected at an output to a terminal of a series circuit comprising means for connecting the electrical load and a current sink, wherein the voltage supplied by the voltage converter is based on an input voltage and on a present multiplication factor; a first comparator circuit, which is electrically connected at a sampling input to the current sink, for receiving a current sink voltage, and which is configured to compare the current sink voltage to a lower threshold value; a second comparator circuit, which is electrically connected at a sampling input to the current sink, for receiving the current sink voltage and for determining an upper threshold value, the upper threshold value being based on the present multiplication factor, based on a new, smaller multiplication factor, based on the lower threshold value, and based on a signal derived from the input voltage, and the second comparator circuit being configured to compare the current sink voltage with the upper threshold value; and selection logic, which is electrically connected to outputs of the first and second comparator circuits and to a control input of the voltage converter, for determining the present multiplication factor, the selection logic being configured to determine a new, larger multiplication factor relative to the present multiplication factor, the new, larger multiplication factor being determined from a set of selectable values if the current sink voltage falls below the lower threshold value, and, the selection logic being configured to determine the new, smaller multiplication factor if the current sink voltage exceeds the upper threshold value.