| 摘要 |
A TIP-RING SHORT DETECTOR AND POWER SHUT-DOWN CIRCUIT FOR A TELEPHONE LINE CIRCUIT A short detector and shut-down circuit is disclosed, for securing feed current to a subscriber loop when abnormal loop conditions are detected. The short detector and shut-down circuit of the present invention includes a tip and ring drive amplifier circuits connected to the tip lead and ring lead respectively, of the subscriber loop. The tip and ring lead amplifier circuits are arranged to convert feed voltage from a central office battery to tip and ring feed currents on the subscriber loop. Each of the tip and ring drive amplifier circuits further include a feed current shutdown circuit arranged to interrupt the feed current developed by their respective amplifier circuit. A common-mode sensing circuit connected to the tip and ring leads is arranged to sense the voltage dropped across the subscriber loop and develop an output voltage of a specific magnitude when an abnormal loop condition is sensed. A detector circuit connected to the common-mode sensing circuit receives the output voltage from the common-mode sensing amplifier circuit and compares the output voltage of the common-mode sensing circuit to a predetermined threshold voltage. The detector circuit outputs a control signal to the tip and ring feed current shut-down circuits when the output voltage crosses into the predetermined threshold voltage range, causing the tip and ring feed current shut-down circuits to shut down the tip and ring drive amplifier circuits, thereby, suspending the tip and ring current fed to the subscriber loop.
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