| 摘要 |
The invention relates to a power supply unit (SCC) for generating a protective current (sealing current), which is superposed on signal currents carried by metal lines for protection against corrosion at tie points or splices of the metal lines, wherein the power supply unit is particularly suited for delivering ANSI T1.601-1992 conformant protective currents (sealing currents) for digital user terminal lines. It exhibits two voltage-controlled power sources (J1, J2), wherein the first power source (J1) is capable, depending on an applied voltage (UC1), of outputting a constant current (I1) having a first value of 0 mA, or a constant current (I1) having a second value of at least 1 mA, in particular 1.2 mA, and wherein the second power source (J2) is capable, under a threshold value, in particular of 0 V, of the applied voltage (UC2), of outputting a constant current (I2) having a third value of 0 mA, and, above the threshold value of the applied voltage (UC2) and proportional to the latter, a current (I2) between the constant current (I2) of the third value and a fourth value of 20 mA diminished at least by the constant current (I1) having the second value of the first power source (J1), as well as at least one voltage input (E2), which is connected with the control input of the second power source (J2) via an integrator (RCI), and a current output (A), with which both the output of the first and the output of the second power source (J1, J2) is connected for outputting the sum of the currents (I1, I2) delivered by both power sources.
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