Current limiter for telephone office signalling

Details Current limiter for telephone office signalling Current limiter for telephone office signalling

1983-03-09

1986-02-25

George, Keith E.

Electrical transmission or interconnection systems

Nonlinear reactor systems

Parametrons

179 18AH, 307255, 307296R, 361152, H03K 1764, H04M 300

Patent

active

045729271

ABSTRACT:
A ring-ground circuit in a telephone system comprises a control transistor that selectively receives base drive from a microprocessor and that has its emitter connected through a low voltage LED and through the series combination of the base-emitter junction of a switching transistor and its emitter resistor to ground. The LED has a sharp transition in its conduction characteristics when the voltage across it reaches a predetermined value which is a reference voltage. Conduction of the control transistor provides base drive to the switching transistor for causing collector current in the latter to initiate a ground-start condition in a relay coil that is connected to a central office battery voltage. When current in the switching transistor increases to a prescribed value, that is set by the LED reference voltage and the emitter resistor, conduction of the switching transistor is automatically controlled for limiting the maximum value of its collector current.

REFERENCES:
patent: 3123746 (1964-03-01), Wachowiak
patent: 3582718 (1971-06-01), Spellman
patent: 4119869 (1978-10-01), Hashimoto
patent: 4224654 (1980-09-01), Golthrop et al.
patent: 4305010 (1981-12-01), Wise
patent: 4323733 (1982-04-01), Ott et al.
patent: 4325019 (1982-04-01), Tezuka
patent: 4384716 (1983-05-01), Powers

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