US 4,374,303 AGranted

Power supply control circuit for subscriber carrier telephone system

AssigneeGTE Automatic Electric Laboratories Incorporated

InventorJames A. Stewart

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Abstract

A control circuit 16 that is responsive to voltage conditions on a cable pair transmission line for selectively disabling a battery charging circuit 12 operating off of line current comprises a resistor R5 and storage capacitor C2 connected in series across the line; a timing capacitor C1 connected between the cathode of a PUT (programmable unijunction transistor) and one wire 32 of the line; and a zener diode D1 between the PUT anode and one wire 32 for establishing a conduction threshold for the PUT. The resistor R5 and primary conduction path of a first bipolar transistor Q2, having its base connected to the PUT anode, are connected in series between the other wire 33 of the line and the charging circuit so that startup current for the charging circuit may be used for charging C2 when the charging circuit is disabled. Means is also included for driving the PUT gate voltage low and turning on the PUT in response to both high and low voltage conditions on the line. This dumps the C2 charge into C1, the latter discharging slowly for holding the charging circuit disabled. A second bipolar transistor Q4 senses the charge voltage on C1 for decreasing the PUT gate voltage when the PUT conducts and for increasing the PUT gate voltage immediately prior to the control circuit enabling the charging circuit to draw line current in order to prevent on-off cycling of the latter on a long cable pair.

Apparatus responsive to prescribed voltage conditions, such as a high voltage that is greater than a first threshold level and a low voltage that is less than a second threshold level, on the pair of wires of a cable pair for rendering a carrier subscriber local battery charging circuit inoperative for at least a prescribed time interval, operation of the charging circuit connecting it through the cable pair to a central office power source from which it draws current for charging the local battery, said apparatus comprising:

first and second lines adapted for electrical connection to one and other of the cable pair wires;
a storage capacitor having one and other terminals electrically connected to said first and second lines, respectively, said storage capacitor being charged with line current on the cable pair that is drawn from the central office power source;
a timing capacitor having a first terminal electrically connected to said first line and having an other terminal;
programmable unijunction transistor (PUT) means having cathode, gate and anode electrodes, said cathode being electrically connected to the other terminal of said timing capacitor;
first means electrically connecting the other terminal of said storage capacitor to said PUT means anode;
second means responsive to both high voltage and low voltage conditions on the cable pair that exceed and fall below the first and second threshold levels for producing a voltage change on said PUT means gate that makes it sufficiently negative with respect to the voltage on said PUT means anode to cause said PUT means to conduct and discharge said storage capacitor into said timing capacitor;
third means responsive to a charge voltage on said timing capacitor for holding the charging circuit inoperative for at least the prescribed time interval during discharge of said timing capacitor following conduction of said PUT means;
and
fourth means responsive to the charge voltage on said timing capacitor for lowering the PUT means gate voltage on conduction of said PUT means and raising the PUT means gate voltage immediately prior to said third means enabling the charging circuit to operate to draw line current on the cable pair for charging the local battery so as to inhibit on-off cycling of the charging circuit.

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Abstract

Claims10