Over-voltage protection circuit for use with a telephone appliance

(54) OVER-VOLTAGE PROTECTION CIRCUIT

FOR USE WITH A TELEPHONE APPLIANCE

(75) Inventors: Minsiu Huang; Jingwei Lin, both of Saratoga, CA (US)

(73) Assignee: ActionTec Electronics, Inc., Sunnyvale, CA (US)

( * ) Notice: Under 35 U.S.C. 154(b), the term of this patent shall be extended for 0 days.

(21) Appl. No.: 09/085,894

(22) Filed: May 27, 1998

(51) Int. C I. I HUM 11/00

(52) U.S. CI 379/412; 379/373

(58) Field of Search 379/412, 373,

379/93.05, 93.36

(56) References Cited

U.S. PATENT DOCUMENTS

3,903,375 9/1975 DeWit 179/18

4,317,964 3/1982 Biggs et al 179/81

4,603,234 7/1986 Huet et al 179/16

4,709,296 11/1987 Hung et al 361/102

4,723,267 2/1988 Jones et al 379/93

4,958,371 9/1990 Damoci et al 379/377

5,042,065 8/1991 Kim 379/165

5,125,027 6/1992 Blaszykowski et al 379/399

5,140,631 8/1992 Stahl 379/377

5,367,569 * 11/1994 Roach et al 379/412

5,369,687 11/1994 Farkas 379/98

5,392,349 * 2/1995 Elder, Jr. 379/412

5,532,898 7/1996 Price 361/119

5,696,660 12/1997 Price 361/119

5,802,151 9/1998 Bevill, Jr. et al 379/93.05

* cited by examiner

Primary Examiner—Stella Woo

(74) Attorney, Agent, or Firm—Fish & Neave; Nicola A. Pisano

(57) ABSTRACT

Over-voltage protection circuitry for use with a PCMCIA modem card or a mobile modem is disclosed. The protection circuitry detects excessive voltage between the tip and ring lines of a telephone subscriber loop when the modem is "off-hook", and immediately places the modem "on-hook", protecting the line interface circuitry, when the over-voltage condition is detected. The over-voltage protection circuitry of the present invention may share common components and signal lines with the modem's ring-detection circuitry, and may be implemented using a minimal number of additional components.

17 Claims, 3 Drawing Sheets