Abstract: A circuit arrangement for supplying electrical energy to a power supply has a fuel cell and an accumulator arrangement. Electrical energy is delivered by the accumulator arrangement during the starting procedure, and is fed into the power supply by the accumulator arrangement via at least one DC/DC converter during starting of the circuit arrangement.

Abstract: A communications system, in particular for a motor vehicle, has a bus line, a central controller which is connected to the bus line, and at least two control modules which are connected to the bus line. The controller and/or at least one of the control modules is capable of combining messages to be sent into a common message which is transmitted onto the bus line The communications system can be used, for example, for fuel-cell electric vehicles.

Abstract: A DC/DC converter which can be operated alternately as a step-up converter in a first direction of energy flow and as a step-down converter in a second direction of energy flow is disclosed. Potential isolation between the low-voltage side and the high-voltage side of the converter is achieved by a magnetic compound unit, which has not only a transformer function but also an energy store function. The converter operates as a push-pull converter in both directions of energy flow. The DC/DC converter can be used for example in motor vehicles with an electric drive fed by fuel cells.