Patent
1982-09-30
1985-01-08
George, Keith E.
179 99H, H04M 100
Patent
active
044928220
ABSTRACT:
A simplified combination of privacy circuit (U1) and holding circuit (U2) for use on a telephone subscriber loop (11). The circuit arrangement includes a diode array (31-34) within a conventional full wave rectifier bridge (21-24) having a pair of interchangeable terminals (28, 29) and a third differentiated terminal (39) for connection in the loop. The interchangeable terminals are connected in series with either the tip or ring conductor with the remaining terminal connected to the other conductor. The combination of diode array and bridge assures that, irrespective of the connection arrangement, the hold circuit always shunts the series combination of telephone and privacy circuit. A novel self limiting amplifier stage including a plurality of diodes (76) shunting the collector to emitter output of a transistor (90) is disclosed for injecting a music-on-hold signal when the hold circuit is active. Additionally, a capacitance (170) in the gate to cathode circuit of a thyristor (46b) in the hold circuit can be charged to a voltage exceeding the on state gate to cathode voltage. A path for discharging the capacitance (182) is provided when the thyristor momentarily shuts off during a momentary loop current interruption to retrigger the SCR solely through the gate to cathode circuit without the use of switching circuits connected to the anode side of the SCR.
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