Telephone lines overvoltage protection apparatus
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United States of America Patent
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-
Jul 10, 1990
Issued Date -
N/A
app pub date -
Apr 20, 1989
filing date -
Mar 4, 1988
priority date (Note) -
Expired
status (Latency Note)
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Abstract
Overvoltage protection arrangements are provided for a pair of telephone lines effective for suppressing noise and transient voltage signals occurring above data and voice signals carried on the telephone lines and that avoids current flow between the telephone lines responsive to common mode voltage signals on the lines so that audible hum is avoided. The overvoltage protection arrangements include first voltage clamping circuitry for clamping voltage signals on the lines at a first predetermined voltage potential and second voltage clamping and filter circuitry for clamping voltage signals on the lines at a second predetermined voltage potential and for filtering noise and transient signals from the voltage signals only when the voltage signals exceed the second predetermined voltage potential. The second voltage clamping circuitry substantially avoids current flow between the lines responsive to common mode voltage signals on the lines.
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