Telephonic communications – Subscriber line or transmission line interface – Protective circuit
Patent
1997-09-15
2000-05-09
Isen, Forester W.
Telephonic communications
Subscriber line or transmission line interface
Protective circuit
379377, 379399, 361119, H04M 1100, H02H 900
Patent
active
060614455
ABSTRACT:
An improved surge protection circuit for withstanding surges is provided. A first node is provided for coupling to a tip lead, and second node is provided for coupling to a ring lead. The surge protection circuit has a first current path for turning on a first transistor, and a second current path for redirecting current from the remaining excess surge energy from one lead to the other lead. The first current path further includes a first sub-path to direct the initial voltage surge to the base electrode of the first transistor to cause the first transistor to turn on hard. The second sub-path redirects current from the initial excess surge energy from the voltage surge to a capacitor prior to the time before the first transistor is fully turned on, so as to protect the base-emitter junction of a second transistor from being reverse biased. The second current path according to the present invention includes the first transistor and a resistor having a first terminal coupled to the emitter electrode of the first transistor and a second terminal coupled to the second node. When the first transistor is fully turned on, the remaining excess voltage is redirected from the tip ring to the lead ring to protect the other circuit elements from damage. A third current path is provided for directing current during an over-voltage condition from one lead to the other lead.
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Rahamim Raphael
Stroud Brian D.
Conexant Systems Inc.
Isen Forester W.
Saint-Surin Jacques
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