Power distribution to provide reliable function of DC/DC converters

Telecommunication systems like switches for public application use a variety of power supply units and modules. The power distribution of 48 V DC for such a system provides the condition that the failure of a single power supply module does not influence the behaviour of the others. Using low power high frequency supply modules on system boards, together with DC/DC power converters of higher power at the same 48 V DC source, calls for further evolution of the distribution system. A first step was shown at the Intelec 96 at Boston: to limit short circuit currents by consequently using impedances already existing in the system. In the second step, the task of conventional fuses is reduced to safely prevent overheating of cables as required by safety standards. Additionally "electronic fuses" are implemented into the system, that are able to limit the currents to values in the order of the nominal working values. The expense is low, if the addition is realised at the right places in the system. The result is a very robust and reliable power distribution architecture, which gives freedom to combine all sorts of power supplies. The application of this new distribution can be seen in the ATM-Switch MainstreetXpress, the alliance product of Siemens and Newbridge.