Power feeding system using two-wire subscriber lines

• US 6,246,748 B1
• Filed: 08/12/1998
• Issued: 06/12/2001
• Est. Priority Date: 08/15/1997
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Yano, Yasuji
• Primary Examiner(s): Korzuch, William R.
• Assistant Examiner(s): Wieland, Susan
• Application Number:
  US09/133,783
• Time in Patent Office: 1,035 Days
• Field of Search: 379/413, 379/22, 379/24, 379/26, 379/27, 379/28, 379/29, 379/30, 379/2, 379/412, 379/5, 379/6, 379/399, 375/258, 375/224, 370/249
• US Class Current: 379/2
• CPC Class Codes: H04M 19/001 Current supply source at the exchanger providing current to substations
• CPC Class Codes: H04M 3/2272 Subscriber line supervision circuits, e.g. call detection circuits
• CPC Class Codes: H04M 3/30 for subscriber's lines , for the local loop

Abstract

A power feeding system includes a line state detector for detecting an operation state of each of a pair of 2-wire subscriber lines connected to the exchange equipment and a transformer for supplying the DC power to the subscriber terminal through each of the pair of 2-wire subscriber lines connected to the subscriber terminal. When the detector detects a subscriber line test state, a switch circuit detaches the transformer from each of the pair of 2-wire subscriber lines and directly connecting the exchange equipment to the subscriber terminal through each of the pair of 2-wire subscriber lines.

Claims

1. A power feeding system for feeding D.C. power to a subscriber terminal using a pair of 2-wire subscriber lines of exchange equipment, the power feeding system comprising:

a detector for detecting the operation state of each of the pair of 2-wire subscriber lines connected to the exchange equipment;

a power supply circuit located between the exchange equipment and the subscriber terminal for supplying the D.C. power to the subscriber terminal through the pair of 2-wire subscriber lines connected to the subscriber terminal; and

a switch circuit for connecting the power supply to the pair of 2-wire subscriber lines when the detector detects that the subscriber lines are in a communication state, and for detaching the power supply from the pair of 2-wire subscriber lines while leaving the exchange equipment connected to the subscriber terminal through the pair of two-wire subscriber lines when the detector detects that the operation state is a subscriber line test state.

2. The power feeding system according to claim 1, wherein the detector detects a voltage between the two wires of each of the pair of 2-wire subscriber lines connected to the exchange equipment to determine whether the operation state is the subscriber line test state.

3. The power feeding system according to claim 1, wherein the detector detects an alternating-current component on each of the pair of 2-wire subscriber lines connected to the exchange equipment to determine whether the operation state is the subscriber line test state, wherein the alternating-current component is applied to each of the pair of 2-wire subscriber lines by the exchange equipment in only a communication state.

4. The power feeding system according to claim 1, wherein the detector comprises:

a first detector for detecting a voltage between the two wires of each of the pair of 2-wire subscriber lines connected to the exchange equipment to produce a first test state detection signal;

a second detector for detecting an alternating-current component on each of the pair of 2-wire subscriber lines connected to exchange equipment to produce a second test state detection signal, wherein the alternating-current component is applied to each of the pair of 2-wire subscriber lines by the exchange equipment in only a communication state; and

a combiner for combining the first and second test state detection signals to produce a switch control signal.

5. The power feeding system according to claim 1, wherein the power supply circuit comprises:

first and second transformers for the first and second 2-wire subscriber lines, respectively, the first transformer having a first winding and a second winding which are detachably connected to the exchange equipment and the subscriber terminal, respectively, the second transformer having a third winding and a fourth winding which are detachably connected to the exchange equipment and the subscriber terminal, respectively, wherein the second and fourth windings having first and second center taps, respectively; and

a DC power source connected to the first and second center taps, and

the switch circuit comprises first and second switch circuits for the first and second transformers, respectively, wherein

the first switch circuit detaches the first transformer from the first 2-wire subscriber line and directly connecting the exchange equipment to the subscriber terminal through the first 2-wire subscriber line when the detector detects the subscriber line test state from the first 2-wire subscriber line; and

the second switch circuit detaches the second transformer from the second 2-wire subscriber line and directly connects the exchange equipment to the subscriber terminal through the second 2-wire subscriber line when the detector detects the subscriber line test state from the second 2-wire subscriber line.

6. The power feeding system according to claim 1, wherein:

the detector comprises a first detection circuit connected to one of the 2-wire subscriber lines and a second detection circuit connected to the other of the 2-wire subscriber lines, each detection circuit being responsive to the connected 2-wire subscriber line being in the test state to generate a control signal; and

wherein

the switch circuit comprises a first switch which connects the power supply circuit to one of the 2-wire subscriber lines and a second switch which connects the power supply circuit to the other of the 2-wire subscriber lines;

the first switch being responsive to the control signal generated by the first detection circuit to disconnect the power supply circuit from the first 2-wire subscriber line, and the second switch being responsive to the control signal generated by the second detection circuit to disconnect the power supply circuit from the second 2-wire subscriber line.

7. The power feeding system according to claim 6, wherein alternating-current signals are applied to the subscriber lines by the exchange equipment only in the communication state;

and wherein the detector detects the absence of the alternating-current signals to determine that the operation state of the subscriber line is the test state.

8. A system for transferring communication signals between exchange equipment and a subscriber terminal using a first 2-wire subscriber line and feeding direct-current (DC) power to the subscriber terminal using a pair of the first 2-wire subscriber line and a second 2-wire subscriber line, comprising:

a detector for detecting an operation state of the pair of 2-wire subscriber lines connected to the exchange equipment to determine whether the operation state is a subscriber line test state;

first and second transformers for the first and second 2-wire subscriber lines, respectively, each of the transformer having a first winding and a second winding, wherein the DC power is applied to center taps of second windings of the first and second transformers; and

first and second switch circuits for the first and second transformers, respectively, wherein the first switch circuit detaches the first transformer from the first 2-wire subscriber line and directly connecting the exchange equipment to the subscriber terminal through the first 2-wire subscriber line and the second switch circuit detaches the second transformer from the second 2-wire subscriber line and directly connecting the exchange equipment to the subscriber terminal through the second 2-wire subscriber line when the detector detects the subscriber line test state.

9. The system according to claim 8, wherein the detector comprises:

a first detector for detecting a voltage between the two wires of each of the pair of 2-wire subscriber lines connected to the exchange equipment to produce a first test state detection signal;

a second detector for detecting an alternating-current component on each of the pair of 2-wire subscriber lines connected to exchange equipment to produce a second test state detection signal, wherein the alternating-current component is applied to each of the pair of 2-wire subscriber lines by the exchange equipment in only a communication state; and

a combiner for combining the first and second test state detection signals to produce a switch control signal.

10. The system according to claim 8, wherein the detector detects a voltage between the two wires of each of the pair of 2-wire subscriber lines connected to the exchange equipment to determine whether the operation state is the subscriber line test state.

11. The system according to claim 8, wherein the detector detects an alternating-current component on each of the pair of 2-wire subscriber lines connected to exchange equipment to determine whether the operation state is the subscriber line test state, wherein the alternating-current component is applied to each of the pair of 2-wire subscriber lines by the exchange equipment in only a communication state.

12. A control method for a power feeding circuit which feeds power to a subscriber terminal using a pair of 2-wire subscriber lines of exchange equipment, the control method comprising the steps of:

a) detecting an operation state of each ofthe pair of 2-wire subscriber lines connected to the exchange equipment;

b) supplying the DC power to the subscriber terminal through the pair of 2-wire subscriber lines connected to the subscriber terminal from a power supply circuit located between the exchange equipment and the subscriber terminal when the operation state is a communication state; and

c) detaching the power supply from the pair of 2-wire subscriber lines while leaving the exchange equipment connected to the subscriber terminal through the pair of 2-wire subscriber lines when the operation state is a subscriber line test state.

13. The control method according to claim 12, wherein the step a) comprises:

detecting a voltage between the two wires of each of the pair of 2-wire subscriber lines connected to the exchange equipment to produce a first test state detection signal;

detecting an alternating-current component on each of the pair of 2-wire subscriber lines connected to the exchange equipment to produce a second test state detection signal, wherein the alternating-current component is applied to each of the pair of 2-wire subscriber lines by the exchange equipment in only a communication state; and

combining the first and second test state detection signals to determine whether the operation state is the subscriber line test state.

14. The control method according to claim 12, wherein the operation state is detected by monitoring a voltage between the two wires of each of the pair of 2-wire subscriber lines connected to the exchange equipment.

15. The control method according to claim 12, wherein the operation state is detected by monitoring an alternating-current component on each of the pair of 2-wire subscriber lines connected to exchange equipment to determine whether the operation state is the subscriber line test state, wherein the alternating-current component is applied to each of the pair of 2-wire subscriber lines by the exchange equipment in only a communication state.

16. A power feeding system for feeding D.C. power to a subscriber terminal in a communication system in which the subscriber terminal is connected to an exchange by a subscriber line, the power feeding system comprising:

a power supply circuit located between the exchange equipment and the subscriber terminal;

a detector for detecting the operation state of the subscriber line; and

a switch circuit for connecting the power supply to the subscriber line when the operating state of the communication system is a communication state, and for disconnecting the power supply from the subscriber line while leaving the exchange equipment connected to the subscriber terminal through the subscriber line when the detector detects that the operation state is a subscriber line test state.

17. The power feeding system according to claim 16, wherein an alternating-current signal is applied to the subscriber line by the exchange equipment only in the communication state;

and wherein the detector detects the absence of the alternating-current signal to determine that the operation state of the subscriber line is the test state.

18. The power feeding system according to claim 16, wherein the detector detects a voltage across the subscriber line to determine if the operation state is the subscriber line test state.

19. The power feeding system according to claim 16, wherein a signal including a time-varying component and a constant component is applied to the subscriber line by the exchange equipment only in the communication state;

and wherein the detector comprises;

a first detection circuit for detecting the absence of the constant component to produce a first test state detection signal;

a second detection circuit for detecting the absence of the time-varying component to produce a second test state detection signal; and

a combiner for combining the first and second test state detection signals to produce a control signal for the switch circuit.

20. The power feeding system according to claim 19, wherein the combiner comprises a logical OR circuit connected to the outputs of the first and second detection circuits.

21. A control method for a power feeding circuit which feeds D.C. power to a subscriber terminal over a subscriber line which connects the subscriber terminal to an exchange, the control method comprising the steps of:

a) detecting an operation state of the subscriber line connected to the exchange equipment;

b) supplying the D.C. power to the subscriber terminal through the subscriber line from a power supply circuit located between the exchange equipment and the subscriber terminal when the operation state is a communication state; and

c) disconnecting the power supply from the subscriber line while leaving the exchange equipment connected to the subscriber terminal through the subscriber line when the operation state is a subscriber line test state.

22. The control method according to claim 21 in which the operation state is detected by monitoring a voltage across the subscriber line.

23. The control method according to claim 21 in which an alternating-current signal is applied to the subscriber line by the exchange equipment only when the operation state is a communication state, and wherein the operation state is detected by monitoring the subscriber line to detect the presence or absence of the alternating-current signal.

24. The control method according to claim 21 in which a signal including a time-varying component and a constant component is applied to the subscriber line by the exchange equipment only in the communication state;

and wherein the step a) comprises;

detecting the absence ofthe constant component to produce a first test state detection signal;

detecting the absence of the time-varying component to produce a second test state detection signal; and

combining the first and second test state detection signals to determine whether the operation state is the subscriber line test state.