LOOP EXTENDER WITH BYPASS CAPACITOR DISCHARGE

摘要

A telephone loop extending circuit for aiding central office battery. Each voltage insertion circuit includes the following: First and second pairs of terminals, first and second voltage sources, first and second transistors having base electrodes and emitter-collector electrode circuits. First sides of the first and second voltage sources, of opposite voltage polarity, are coupled to a first terminal of the corresponding pair. One side of the emitter-collector electrode circuit of each of the transistors is coupled to a second terminal of the corresponding pair. The other sides of the emitter-collector electrode circuits of the first and second transistors are individually coupled to second sides of, respectively, the first and second voltage sources. First and second optical coupling means are provided for the first and second transistors, respectively, each for sensing current flow between terminals of a pair and each being responsive to current flow in one of two opposite directions between terminals for enabling the corresponding transistor to couple the corresponding voltage source to the second terminal of the corresponding pair. A bypass capacitor is coupled from one terminal to the other of the corresponding pair for passing selected signals around the transistors and voltage sources from terminal to terminal. A resistor is coupled from the base electrodes of both transistors to the first sides of the voltage sources and is operative in combination with at least one of the transistors for providing a discharge path for the bypass capacitor after an externally applied signal is removed from terminals of the corresponding pair.