Single line telephone hold circuit

Details Single line telephone hold circuit Single line telephone hold circuit

1977-03-14

1978-06-06

Claffy, Kathleen H.

179 99, H04M 100

Patent

active

040938298

ABSTRACT:
A solid-state circuit for maintaining line current in a two-wire telephone line placed on "HOLD" by the subscriber. A shunt impedance is connected in series with a pair of transistor switches, the first of which conducts only when the telephone line voltage is lower than a predetermined value and the second of which conducts whenever a momentary contact switch is manually actuated. The second transistor continues to conduct until a subsequent substantial decrease in telephone line voltage, indicative of a renewed off-hook condition, is detected.

REFERENCES:
patent: 3725600 (1973-04-01), Hutton
patent: 3742151 (1973-06-01), Ruether
patent: 3870831 (1975-03-01), McCarley
patent: 3997734 (1976-12-01), Champan
patent: 4001520 (1977-01-01), Waldman

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