| 摘要 |
A loop extender is used in conjunction with a pair of telephone lines extending from a telephone central office to a subscriber location in order to insert a booster DC potential on the telephone lines in such a manner as to aid the flow of DC current produced on the telephone lines by a telephone central office battery. A control circuit has one input terminal coupled to one of the telephone lines and a reference terminal, another input terminal coupled to the other telephone line and the reference terminal, and an output terminal coupled to a relay. Whenever the input terminals are supplied with a specified potential from the telephone lines, an output from the output terminal maintains the relay in a nonenergized condition so that contacts controlled by the relay couple a DC booster power supply in series relationship with one of the telephone lines. In response to different potentials on the input terminals, the output at the output terminal energizes the relay such that the contacts insert the DC booster power supply in series relationship with the other telephone line. The DC booster power supply has a current sensor such that the booster DC potential is only supplied to the telephone lines when DC current is present on the telephone lines. In addition, the DC booster power supply has a current limiter limiting the amount of DC current on the telephone lines. |
