Telephone interface circuit

Details Telephone interface circuit Telephone interface circuit

2006-07-06

2010-10-26

Tsang, Fan (Department: 2614)

Telephonic communications

Subscriber line or transmission line interface

Protective circuit

C379S402000, C379S403000, C379S413010

Reexamination Certificate

active

07822195

ABSTRACT:
A telephone interface circuit comprises a first transistor for controlling opening and closing between a speech circuit and subscriber lines, a second transistor for controlling the first transistor to turn on and off, a positive feedback circuit connecting a collector terminal of the first transistor and a base terminal of the second transistor, an overcurrent detection circuit detecting overcurrent applied to the subscriber lines, and a breaker circuit for turning off the first transistor by lowering the base potential of the second transistor to a low potential when overcurrent is detected at the overcurrent detection circuit. Here, the base terminal of the first transistor and a collector terminal of the second transistor are connected. Further, when off-hook, the base potential of the second transistor is controlled in such a manner as to become a high potential by a microcomputer.

REFERENCES:
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patent: 4580011 (1986-04-01), Glaser
patent: 4694483 (1987-09-01), Cheung
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patent: 5392349 (1995-02-01), Elder, Jr.
patent: 6418222 (2002-07-01), Wong et al.
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patent: 2008/0037772 (2008-02-01), Fujiwara
patent: 2008/0181391 (2008-07-01), Fujiwara
patent: 2008/0285741 (2008-11-01), Fujiwara
Co-pending U.S. Appl. No. 12/268,895, filed Nov. 11, 2008.

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