Patent
1976-09-29
1977-08-09
Robinson, Thomas A.
H04B 346
Patent
active
040412555
ABSTRACT:
A switching circuit includes a magnetically latching relay and associated contacts connected between a subscriber loop and associated subscriber equipment. In one state of latched operation the subscriber equipment is connected to the loop via the contacts and in the other state of latched operation the subscriber equipment is disconnected from the loop. To operate the relay a voltage is applied to the loop, the voltage being of sufficient value to charge a capacitor in the switching circuit to the threshold voltage of a PNPN diode which is connected in series with the operate coil in the latching relay. The PNPN diode discharges the capacitor through the operate coil to cause the relay to latch magnetically in a make or break state depending upon the polarity of the discharge current. An AC resonantly responsive relay is added to the switching circuit to selectively inhibit switching circuit response in the case where more than one switching circuit is utilized on a loop. Hence different subscriber equipments can be selectively connected or disconnected as required.
REFERENCES:
patent: 3636280 (1972-01-01), Wetzel
patent: 3725613 (1973-04-01), Allen et al.
patent: 3739107 (1973-06-01), Spencer
patent: 3766336 (1973-10-01), Wikholm
patent: 3773986 (1973-11-01), Tremblay
patent: 3867588 (1975-02-01), Pickens
patent: 3919487 (1975-11-01), Gabrielson
Cambridge Ronan Malcolm
Watson Douglas John
Northern Telecom Limited
Robinson Thomas A.
Turpin Frank
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