Telephone interface circuit

• US 7,822,195 B2
• Filed: 07/06/2006
• Issued: 10/26/2010
• Est. Priority Date: 07/06/2006
• Status: Expired due to Fees

• Current Assignee: Uniden Corporation (Cornwall Capital Management LP)
• Original Assignee: Uniden Corporation (Cornwall Capital Management LP)
• Inventors: Fujiwara, Yoshinobu
• Primary Examiner(s): Tsang; Fan
• Assistant Examiner(s): Sharifzada; Ibraham
• Application Number:
  US11/481,583
• Publication Number:
  US 20080037773A1
• Time in Patent Office: 1,573 Days
• Field of Search: 37939901-41304
• US Class Current: 379/412
• CPC Class Codes: H04M 1/745 Protection devices or circuits for voltages surges on the line

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.

Claims

1. A telephone interface circuit comprising:

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;

a terminal connecting the base terminal of the second transistor and a microcomputer;

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 the overcurrent is detected at the overcurrent detection circuit,

wherein the base terminal of the first transistor and a collector terminal of the second transistor are connected, and

when off-hook, the base potential of the second transistor is controlled in such a manner as to become a high potential by the microcomputer via the terminal.

2. The telephone interface circuit of claim 1, wherein the second transistor is made to self-return from being turned off to being turned on by the base potential of the second transistor being pulled up to a high potential by a microcomputer after being pulled down to a low potential by the breaker circuit.

3. The telephone interface circuit of claim 2, wherein the period the first transistor is disconnected for is longer for larger overvoltages applied to the subscriber lines.