Overload protection circuit for a telephone subscriber line feed

Details Overload protection circuit for a telephone subscriber line feed Overload protection circuit for a telephone subscriber line feed

1985-12-05

1988-01-05

Ng, Jin F.

Telephonic communications

Subscriber line or transmission line interface

Protective circuit

379413, H04M 1900

Patent

active

047180846

ABSTRACT:
One arm of a subscriber line battery feed circuit (Ra, Rb, B) contains a FET transistor (TrL) as a current limiting element which, when a limit value of feed current is reached, is operated in such manner that it limits the feed current. If the limiting operation exceeds a first time interval, the feed circuit is interrupted by the blockage of the transistor. The transistor cannot resume the conductive state until the elapse of a second, longer time interval which is sufficient for cooling the transistor. The threshold value is not rigid but changes in accordance with the amplitude and direction of interference longitudinal currents which are superimposed upon the feed current.

REFERENCES:
patent: 4211895 (1980-07-01), Davis et al.
patent: 4398066 (1983-08-01), Sinberg
patent: 4465903 (1984-08-01), Barber
patent: 4525602 (1985-06-01), Robra et al.

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