H - Electricity – 04 – M
Patent
H - Electricity
04
M
379/63, 379/67,
H04M 7/00 (2006.01) H04M 3/18 (2006.01) H04M 19/00 (2006.01)
Patent
CA 1175587
PHN 9939 18 23.7.1981 ABSTRACT: "Telephone subscriber's line circuit with overvoltage protection". A telephone subscriber's line circuit includes a control stage for applying a current to or absorbing a current from the subscriber's line (8) and comprises an amplifier (1). The circuit has two terminals (2,3 ) for connection to a power source and first and second diodes (6, 7) are connected between the terminals (2, 3) and power supply terminals ( 1-1, 1-2) of the amplifier (1). The diodes (6, 7) are poled to conduct during normal operation of the circuit but when an overvoltage which is greater than that supplied at the terminal 2 or 3 is induced on the line (8) one of the diodes (6, 7) is reversed biassed and becomes non-conducting. Further diodes (11, 18) and (12, 19) prevent the output transistors (4, 5) of the amplifier (1) being subjected to high voltages which could cause breakdown of their base-emitter junctions. Voltage-limiting elements (13, 14) are connected between the line (8) and the system earth to provide a discharge path for currents in- duced on the line (8).
394202
N.v. Philips Gloeilampenfabrieken
Van Steinburg C.e.
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