A circuit, having a plurality of regulated, parallel, voltage sources, an a.c.-d.c. converter circuit and a regulating unit, and a method for controlling it. The regulated voltage sources include an unregulated voltage source of a temporally variable output d.c. voltage, a step-up converter and an associated regulating device, where the step-up converter is a three-point step-up converter. The regulating unit measures the intermediate circuit voltage of the a.c.-d.c. converter circuit and is connected with the regulating devices. In the method for control, the regulating unit determines the voltage in the intermediate circuit of the a.c.-d.c. converter circuit and from this determines, as a function of the maximally and minimally permissible intermediate circuit voltage, a set-point value for the output voltage of the regulated voltage sources. This set-point value is transmitted to the regulating devices, from which the regulating devices determine the control conditions for the step-up converter.