Telephone key systems and key stations therefor

Details Telephone key systems and key stations therefor Telephone key systems and key stations therefor

1985-05-13

1987-03-31

Dwyer, James L.

Telephonic communications

Multi-line or key substation system with selective switching...

379387, 379413, H04M 1900

Patent

active

046548700

ABSTRACT:
In a telephone key system including a central branch exchange and a plurality of key stations, each key station includes a switch-mode power supply unit and derives logic circuit drive power by converting unregulated high tension d.c. voltage power from the exchange to regulated low tension logic level voltage. In the preferred arrangement each key station includes WAL II code signalling receive and transmit circuits and burst mode signalling is adopted. The transformers of these circuits are center-tapped for transformer phantom coupling to the switch-mode power supply unit, and are connected to the exchange by a 2-way 4-wire line. The switch-mode power supply unit is preferably of flyback configuration and includes thus a controlled transistor switch, a transformer, a rectifier, and a switch-mode power supply controller to control on/off operation of the switch for voltage regulation.

REFERENCES:
patent: 3843845 (1974-10-01), Ridley
patent: 4081615 (1978-03-01), Hoehn
patent: 4173714 (1979-11-01), Bloch et al.
patent: 4203011 (1980-05-01), Coviello
patent: 4392024 (1983-07-01), Shinoi et al.
patent: 4410767 (1983-10-01), Sekiguchi

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