1980-07-03
1981-12-15
Brigance, Gerald L.
179 18FA, 179 81R, H04M 131, H04M 1900
Patent
active
043061192
ABSTRACT:
In a telephone system wherein a polarity reversible dc voltage is provided by a central office, a telephone outpulsing circuit utilizing field-effect transistors (21-24) performs the additional function of a polarity guard. Arranged in a rectifying configuration, the field-effect transistors connect the telephone line (10, 11) from a central office to a telephone set requiring a single polarity. The low ON resistance of the field-effect transistors consumes relatively little power from the central office, thus allowing a higher voltage to the telephone set than is available with a conventional polarity guard. The circuit also performs a switchhook flash function and senses the voltage on the telephone line such that if a predetermined level is exceeded, the field-effect transistors are turned OFF and this higher voltage is prevented from reaching the telephone set.
REFERENCES:
patent: 3932707 (1976-01-01), Connolly et al.
patent: 3973084 (1976-08-01), Hovland
patent: 4046971 (1977-09-01), Losehand
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patent: 4081619 (1978-03-01), Losehand
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patent: 4167655 (1979-09-01), Hestad et al.
patent: 4223186 (1980-09-01), Hartmann
"Semiconductors Provide New Features" Telephony Oct. 29, 1979, pp. 60, 64-66, 68, 69, and 101, Victor Godbole.
Bell Telephone Laboratories Incorporated
Brigance Gerald L.
Williamson Samuel R.
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