Patent Number: 7,822,195

Title: Telephone interface circuit

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.

Inventors: Fujiwara; Yoshinobu (Tokyo, JP)

Assignee: Uniden Corporation

International Classification: H04M 1/00 (20060101)

Expiration Date: 2018-10-26 0:00:00