Telephone circuit

Patent

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Details

179 16F, 179 81B, H04M 100, H04M 160, H04M 176

Patent

active

045061149

ABSTRACT:
A telephone speech and signalling circuit includes an integrated circuit powered by the exchange battery through the subscriber's line. The power supply for the integrated circuit is maintained during short duration line breaks caused by operations within the exchange by the charge on a capacitor which is charged from the exchange battery through the collector-emitter path of a first transistor when the subscriber's line is looped. The driving current for the first transistor is supplied by a second transistor. The integrated circuit compares the line voltage with the voltage across the capacitor, and reduces the driving current for the second transistor when the line voltage falls below the capacitor voltage. This reduces the driving current for the first transistor, reducing its conductivity to a level which prevents significant discharge of the capacitor but nevertheless allows line voltage to be discharged through the two transistors.

REFERENCES:
patent: 3780228 (1973-12-01), Stewart

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