Telephone interface circuit
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United States of America Patent
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-
Aug 9, 2011
Grant Date -
Jul 31, 2008
app pub date -
Jan 31, 2007
filing date -
Jan 31, 2007
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
A hook switch turns on a transistor by connecting the positive electrode terminal of a capacitor to a base terminal of a transistor in an off-hook state, causing a speech circuit and telephone lines to be connected. The hook switch turns off the transistor by disconnecting the positive electrode terminal of the capacitor from the base terminal of the transistor in an on-hook state, causing the speech circuit and the telephone lines to be disconnected. A holding circuit holds the voltage at the positive electrode terminal of the capacitor at a substantially fixed value by charging the capacitor with electric power supplied from the telephone lines in an off-hook state.
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