SYSTEM FOR PROVIDING VOLTAGE IN A VOLTAGE LINE COMMON TO A PLURALITY OF ELECTRICAL UNITS

摘要

The present invention relates to a system for providing voltage to a common line (6) for a plurality of electrical units (U1, ..., UN-1, UN). Each electrical unit (U1...UN) comprises a power suppluy unit (1) for supplying power to the electrical circuits (2, 3) of the electrical unit (U1...UN) and to said common voltage line (6). A switch (4) is provided between the power supply unit (1) and the voltage line (6) to be in such position while the power supply unit (1) is in operation that the power supply unit (1) supplies power to said voltage line (6), and in another position while the power supply unit is not in operation, whereby at least some (3) of the electrical circuits (2, 3) of the electrical unit (U1...UN) take voltage from said common voltage line (6). In addition, a protection resistor (5) is provided between the switch (4) and the voltage line (6) for protecting both the auxiliary voltage line (6) and the electrical unit (U1...UN) against a great magnitude of current caused by a damage. With the invention, a reliable and accurate voltage supply to the common line (6) is produced, and it is well appropriate for the purposes of telecommunications systems for providing auxiliary voltage to interface circuits (3) of plug-in units in order to have said plug-in units (U1...UN) connected disturbance-free to a common data transfer bus (7).