Protection circuit for telephone systems

Details Protection circuit for telephone systems Protection circuit for telephone systems

1995-06-07

1997-06-10

Zele, Krista M.

Telephonic communications

Subscriber line or transmission line interface

Protective circuit

379413, 379418, 379398, 379 27, 379 30, H04M 306, H04M 124

Patent

active

056384408

ABSTRACT:
A power-cross detection circuit includes a zero crossing detection circuit for detecting a first zero crossing of the current from a first positive half-cycle to a first negative half-cycle, a second zero crossing of the current from a second positive half-cycle to a second negative half-cycle, and a third zero crossing of the current from a third positive half-cycle to a third negative half-cycle and a circuit for detecting a voltage level and outputting a first signal when the voltage level exceeds a predetermined voltage level, between the first zero crossing and the second zero crossing and between the second zero crossing and the third zero crossing. The zero crossing detection circuit outputs a second signal based on the first, second and third zero crossings. The power-cross detection circuit also includes a logic circuit for outputting a third signal when the time interval between the first zero crossing and the second zero crossing and between the second zero crossing and the third zero crossing is between 14 milliseconds and 24 milliseconds. A power-cross condition is detected based on the first, second and third signals.

REFERENCES:
patent: 3996426 (1976-12-01), Lancaster
patent: 4079210 (1978-03-01), Sanderson
patent: 4995111 (1991-02-01), Tojo et al.
patent: 5038375 (1991-08-01), Sinberg
patent: 5323461 (1994-06-01), Rosenbaum et al.
patent: 5402482 (1995-03-01), Minohara et al.
patent: 5406623 (1995-04-01), Rovik
patent: 5426695 (1995-06-01), Misu
patent: 5440612 (1995-08-01), Siligoni et al.

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