Line current protection circuit and method for use with a PCMCIA-architecture modem card
US5777836A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Mar 19, 1997 |
| Grant date | Jul 7, 1998 |
| Priority date | — |
| Expiry date | Mar 19, 2017 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04M11/06
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
A novel line-current protection circuit and method that is useable with a PCMCIA modem card is disclosed. The protection circuit is adapted to detect when an excessive voltage is present across the tip and the ring leads of a telephone subscriber loop by sensing the amount of line-current being supplied to line interface circuitry disposed on the PCMCIA modem card. The protection circuit includes a current sensing circuit portion that is placed in series with the tip lead and which detects when the line current exceeds a predetermined maximum amount. In the event the line current exceeds the maximum, the current sensing circuit asserts an excessive line current signal. A control and delay circuit causes the relay circuit to open the electrical connection between the modem and the telephone line only when the line current exceeds a predetermined maximum amount for a minimum amount of time. The protection circuit also includes a backup fuse, which will trip if the primary components of the protection circuit fail.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.