Test-through voltage booster circuit for telephone systems

Claim 2

In a circuit adapted to introduce a d-c boost voltage in series with a subscriber line when operating current flows therethrough and to withhold such d-c boost voltage when test current flows therethrough, in combination, a central office terminal, a subscriber terminal, bi-directional switching means for conducting or blocking the flow of current between said terminals, through said bi-directional switching means, means for establishing a d-c boost voltage of a first polarity between said terminals when current flows through said bi-directional switching means in a first direction and has a magnitude which exceeds a first predetermined value, means for establishing a d-c boost voltage of a second polarity between said terminals when current flows through said bi-directional switching means in a second direction and has a magnitude which exceeds a second predetermined value, means for bypassing said switching means and for conducting current between said central office and subscriber terminals when said bi-directional switching means is nonconducting, and means for connecting said switching means in voltage responsive relationship to said central office terminal to conduct when the driving voltage at said central office terminal exceeds a predetermined value and to block when the driving voltage at said central office terminal is less than said predetermined value.

Claim 3

A circuit as set forth in claim 1 in which the magnitudes of said first and second predetermined values exceed the magnitude of the highest low magnitude test current which is to be passed between said central office terminal and said subscriber terminal.

Claim 4

A circuit as set forth in claim 1 in which said bi-directional switching means comprises a PNP transistor and an NPN transistor having interconnected connector-emitter circuits to provide current flow in either direction through said bi-directional switching means and having interconnected base-emitter circuits, and in which said means for connecting said bi-directional switching means in voltage responsive relationship to said central office terminal comprises first resistance means connected across the base-emitter circuits of said transistors, second resistance means for connecting said base-emitter circuits across the source of driving voltage for said central office terminal and third resistance means for connecting said base-emitter circuits between said central office terminal and ground.

Claim 5

In a circuit adapted to introduce a d-c boost voltage in series with a subscriber line when operating current flows therethrough and to withhold such d-c boost voltage when test current flows therethrough, in combination, central office terminal means, subscriber terminal means, voltage insertion means having input means and output means, means in said voltage insertion means for establishing between said input and output means a d-c boost voltage of a first polarity when current flowing in a First direction through the input means thereof exceeds a first predetermined value anad for establishing between said input and output means a d-c boost voltage of a second polarity when current flowing in a second direction through the input means thereof exceeds a second predetermined value, bi-directional switching means for connecting said input means to said central office terminal means, bypassing means for bypassing said switching means and for conducting current between said central office terminal means and said subscriber terminal means when said switching means is non-conducting, means for connecting said output means to said subscriber terminal means, and means for maintaining said bi-directional switching means non-conducting when the voltage applied to said central office terminal means is less than a predetermined value.

Claim 6

In a circuit adapted to introduce a d-c boost voltage in series with a subscriber line when operating current flows therethrough and to withhold such d-c boost voltage when test current flows therethrough, in combination, central office terminal means, subscriber terminal means, voltage insertion means having input means and output means, means in said voltage insertion means for establishing between said input and output means a d-c boost voltage of a first polarity when current flowing in a First direction through the input means thereof exceeds a first predetermined value anad for establishing between said input and output means a d-c boost voltage of a second polarity when current flowing in a second direction through the input means thereof exceeds a second predetermined value, bi-directional switching means for connecting said input means to said central office terminal means, bypassing means for bypassing said switching means and for conducting current between said central office terminal means and said subscriber terminal means when said switching means is non-conducting, means for connecting said output means to said subscriber terminal means, and means for maintaining said bi-directional switching means non-conducting when the voltage applied to said central office terminal means is less than a predetermined value.

Claim 7

A circuit as set forth in claim 4 in which said bi-directional switching means comprises a PNP transistor and an NPN transistor having interconnected collector-emitter circuits to provide current flow in either direction through said bi-directional switching means, and having interconnected bases.

Claim 8

A circuit as set forth in claim 5 in which said bypassing means comprises resistance means connected across the base-emitter circuits of said transistors.

Claim 9

In a circuit adapted to introduce a d-c boost voltage in series with a subscriber line when operating current flows therethrough and to withhold such d-c boost voltage when test current flows therethrough, in combination, central office terminal means, subscriber terminal means, a voltage insertion network having an operating input, a test input and an output, means in said voltage insertion network for establishing between said operating input and said output a d-c boost voltage of a first polarity when current flowing in a first direction through the operating input thereof exceeds a first value and for establishing between said operating input and said output a d-c boost voltage of a second polarity when current flowing in a second direction through the operating input thereof exceeds a second value, means for conducting current between said test input and said output without establishing a d-c boost voltage therebetween, means for connecting said output to said subscriber terminal means, bi-directional switching means for connecting said central office terminal means to said operating input, means for bypassing said switching means when said switching means is non-conducting and means for maintaining said bi-directional switching means non-conducting when test voltages having magnitudes less than a predetermined value are applied to said central office terminal means.

Claim 10

In a circuit adapted to introduce a d-c boost voltage in series with a subscriber line when operating current flows therethrough and to withhold such d-c boost voltage when test current flows therethrough, in combination, central office terminal means, subscriber terminal means, a voltage insertion network having an operating input, a test input and an output, means in said voltage insertion network for establishing between said operating input and said output a d-c boost voltage of a first polarity when current flowing in a first direction through the operating input thereof exceeds a first value and for establishing between said operating input and said output a d-c boost voltage of a second polarity when current flowing in a second direction through the operating input thereof exceeds a second value, means for conducting current between said test input and said output without establishing a d-c boost voltage therebetween, means for connecting said output to said subscriber terminal means, bi-directional switching means for connecting said central office terminal means to said operating input, means for bypassing said switching means when said switching means is non-conducting and means for maintaining said bi-directional switching means non-conducting when test voltages having magnitudes less than a predetermined value are applied to said central office terminal means.

Claim 11

A circuit as set forth in claim 7 in which said bi-directional switching means comprises a PNP transistor and an NPN transistor having interconnected emitter electrodes, interconnected collector electrodes and interconnected base electrodes, and in which said means for connecting said central office terminal means to said test input comprises a bypass resistor connected across base-emitter circuits of said transistors.

Claim 12

In a circuit adapted to introduce a d-c boost voltage in series with a subscriber line when operating current flows therethrough and to withhold such d-c boost voltage when test current flows therethrough, in combination, central office terminal means, subscriber terminal means, voltage insertion means having input means and output means, means in said voltage insertion means for establishing between said input and output means a d-c boost voltage of a first polarity when current flowing in a first direction through the input means thereof exceeds a first predetermined value and for establishing between said input and output means a d-c boost of a second polarity when current flowing in a second direction through the input means thereof exceeds a second predetermined value, current responsive means for controlling the voltage between said input and output means in accordance with the Flow of current through said input means, said voltage booster circuit including a non-boosting path for conducting current between said input and output means when the flow of current through said current responsive means is between said first and second predetermined values, means for connecting said output means to said subscriber terminal means, bi-directional switching means for connecting said input means to said central office terminal means, bypass means for bypassing said switching means and for conducting current from said central office terminal means to said non-boosting path when said bi-directional switching means is non-conducting, and means for maintaining said bi-directional switching means non-conducting when test voltages having magnitudes less than a predetermined value are applied to said central office terminal means.

Claim 13

In a circuit adapted to introduce a d-c boost voltage in series with a subscriber line when operating current flows therethrough and to withhold such d-c boost voltage when test current flows therethrough, in combination, central office terminal means, subscriber terminal means, voltage insertion means having input means and output means, means in said voltage insertion means for establishing between said input and output means a d-c boost voltage of a first polarity when current flowing in a first direction through the input means thereof exceeds a first predetermined value and for establishing between said input and output means a d-c boost of a second polarity when current flowing in a second direction through the input means thereof exceeds a second predetermined value, current responsive means for controlling the voltage between said input and output means in accordance with the Flow of current through said input means, said voltage booster circuit including a non-boosting path for conducting current between said input and output means when the flow of current through said current responsive means is between said first and second predetermined values, means for connecting said output means to said subscriber terminal means, bi-directional switching means for connecting said input means to said central office terminal means, bypass means for bypassing said switching means and for conducting current from said central office terminal means to said non-boosting path when said bi-directional switching means is non-conducting, and means for maintaining said bi-directional switching means non-conducting when test voltages having magnitudes less than a predetermined value are applied to said central office terminal means.

Claim 14

In a circuit adapted to introduce a d-c boost voltage in series with a subscriber line when operating current flows therethrough and to withhold such d-c boost voltage when test current flows therethrough, in combination, central office terminal means, subscriber terminal means, line current indicating means for indicating the magnitude and direction of current flow between said central office and subscriber terminal means, bi-directional switching means for conducting or blocking the flow of current through said indicating means, first and second boost voltage supply means, first and second variable conducting means for connecting respective boost voltage supply means between said central office and subscriber terminal means through said switching means, control means for connecting said line current indicating means to said first and second variable conducting means, respectively, to control the conduction thereof when the current through said indicating means exceeds respective first and second threshold values, said variable conducting means being adapted to conduct current between said central office and subscriber terminal means without establishing a d-c boost voltage therebetween when the current through said line current indicating means is between said first and second threshold values, current bypassing means for bypassing current around said line current indicating means and said bi-directional switching means when said switching means is in its blocking condition and means for maintaining said switching means in its conducting condition when the voltage applied to said central office terminal means exceeds a predetermined value.

Claim 15

In a circuit adapted to introduce a d-c boost voltage in series with a subscriber line when operating current flows therethrough and to withhold such d-c boost voltage when test current flows therethrough, in combination, central office terminal means, subscriber terminal means, line current indicating means for indicating the magnitude and direction of current flow between said central office and subscriber terminal means, bi-directional switching means for conducting or blocking the flow of current through said indicating means, first and second boost voltage supply means, first and second variable conducting means for connecting respective boost voltage supply means between said central office and subscriber terminal means through said switching means, control means for connecting said line current indicating means to said first and second variable conducting means, respectively, to control the conduction thereof when the current through said indicating means exceeds respective first and second threshold values, said variable conducting means being adapted to conduct current between said central office and subscriber terminal means without establishing a d-c boost voltage therebetween when the current through said line current indicating means is between said first and second threshold values, current bypassing means for bypassing current around said line current indicating means and said bi-directional switching means when said switching means is in its blocking condition and means for maintaining said switching means in its conducting condition when the voltage applied to said central office terminal means exceeds a predetermined value.

Claim 16

In a circuit adapted to introduce a d-c boost voltage in series with a subscriber line when operating current flows therethrough and to withhold such d-c boost voltage when test current flows therethrough, in combination, central office terminal means, subscriber terminal means, line current indicating means for indicating the magnitude and direction of current flow between said central office and subscriber terminal means, bi-directional switching means for conducting or blocking the flow of current through said indicating means, first and second boost voltage supply means, means for connecting said switching means, said indicating means, said first voltage supply means and said first variable conducting means in a first closed path between said central office and subscriber terminal means, means for connecting said switching means, said indicating means, said second voltage supply and said second variable conducting means in a second closed path between said central office and subscriber terminal means, control means for controlling the conduction of said variable conducting means in accordance with the magnitude and direction of current flow through said indicating means, bypassing means for bypassing said switching means and for conducting current between said central office and subscriber terminal means when said switching means blocks the flow of current through said indicating means and means for establishing the blocking state of said switching means when a voltage less than a predetermiNed voltage is applied between said central office terminal means and ground or when a voltage less than said predetermined voltage is applied to said central office terminal means.

Claim 17

In a circuit adapted to introduce a d-c boost voltage in series with a subscriber line when operating current flows therethrough and to withhold such d-c boost voltage when test current flows therethrough, in combination, central office terminal means, subscriber terminal means, line current indicating means for indicating the magnitude and direction of current flow between said central office and subscriber terminal means, bi-directional switching means for conducting or blocking the flow of current through said indicating means, first and second boost voltage supply means, means for connecting said switching means, said indicating means, said first voltage supply means and said first variable conducting means in a first closed path between said central office and subscriber terminal means, means for connecting said switching means, said indicating means, said second voltage supply and said second variable conducting means in a second closed path between said central office and subscriber terminal means, control means for controlling the conduction of said variable conducting means in accordance with the magnitude and direction of current flow through said indicating means, bypassing means for bypassing said switching means and for conducting current between said central office and subscriber terminal means when said switching means blocks the flow of current through said indicating means and means for establishing the blocking state of said switching means when a voltage less than a predetermiNed voltage is applied between said central office terminal means and ground or when a voltage less than said predetermined voltage is applied to said central office terminal means.

Claim 18

In a current adapted to introduce a d-c boost voltage in series with a subscriber line when operating current flows therethrough and to withhold such d-c boost voltage when test current flows therethrough, in combination, first and second voltage booster networks each having a central office terminal and a subscriber terminal, means for connecting said voltage booster networks in series with respective conductors of a subscriber line, each of said voltage booster networks including: a voltage insertion network having an input and an output, means in said voltage insertion network for establishing between said input and output a d-c boost voltage of a first polarity when current flowing in a first direction through the input thereof exceeds a first predetermined value and for establishing between said input and output a d-c boost voltage of a second polarity when current flowing in a second direction through the input thereof exceeds a second predetermined value, bi-directional switching means for connecting said input to said central office terminal, bypassing means for bypassing said switching means and for conducting current between said central office terminal and said subscriber terminal when said switching means is non-conducting, means for connecting said output to said subscriber terminal and means for maintaining said bi-directional switching means non-conducting when the voltage at said central office terminal is less than a predetermined value.

Claim 19

In a current adapted to introduce a d-c boost voltage in series with a subscriber line when operating current flows therethrough and to withhold such d-c boost voltage when test current flows therethrough, in combination, first and second voltage booster networks each having a central office terminal and a subscriber terminal, means for connecting said voltage booster networks in series with respective conductors of a subscriber line, each of said voltage booster networks including: a voltage insertion network having an input and an output, means in said voltage insertion network for establishing between said input and output a d-c boost voltage of a first polarity when current flowing in a first direction through the input thereof exceeds a first predetermined value and for establishing between said input and output a d-c boost voltage of a second polarity when current flowing in a second direction through the input thereof exceeds a second predetermined value, bi-directional switching means for connecting said input to said central office terminal, bypassing means for bypassing said switching means and for conducting current between said central office terminal and said subscriber terminal when said switching means is non-conducting, means for connecting said output to said subscriber terminal and means for maintaining said bi-directional switching means non-conducting when the voltage at said central office terminal is less than a predetermined value.

Claim 20

A circuit as set forth in claim 12 in which each of said bi-directional switching means comprises a PNP transistor and an NPN transistor having collector-emitter circuits interconnected to provide current flow in either direction through said bi-directional switching means and having interconnected bases, and in which each of said bypassing means comprises resistance means connected across the base-emitter circuits of the transistors of the respective bi-directional switching means.

Claim 21

A circuit as set forth in claim 12 in which each of said bi-directional switching means comprises a PNP transistor and an NPN transistor having interconnected collector-emitter circuits to provide current flow in either direction through said bi-directional switching means and having interconnected bases, and in which said means for maintaining said bi-directional switching means non-conducting comprises resistance means for connecting the base-emitter circuits of said transistors between said central office terminals and to ground.