| 摘要 |
<p>When a floating battery feed circuit is used to power telephone lines, it is desirable to provide an anti-corrosion biasing circuit (300) to keep the voltage on the tip and ring conductors from becoming positive. This can be done using an anti-corrosion circuit (300) that sinks a dynamic amount of current from the tip conductor. A line circuit including such biasing is, however, incompatible with special lines such as PBX lines that rely on a grounded tip conductor in the talk state. In accordance with the present invention, a constant current is supplied from a ground reference circuit (400) to the ring conductor of such special lines only when loop current is flowing. The magnitude of this supplied current is such that the anti-corrosion circuit (300) holds the tip conductor sufficiently close to ground potential to allow the proper operation of circuits connected to the special lines.</p> |
