Power feeding system using two-wire subscriber lines

Details Power feeding system using two-wire subscriber lines Power feeding system using two-wire subscriber lines

1998-08-12

2001-06-12

Korzuch, William R. (Department: 2641)

Telephonic communications

Diagnostic testing, malfunction indication, or electrical...

Including fault responsive disconnection of tested component

C379S399010, C379S412000, C379S413000

Reexamination Certificate

active

06246748

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a system for feeding electric power to a terminal using a subscriber line, and in particular to a system having a power feeding circuit provided between exchange or switch equipment and the terminal.
2. Description of the Related Art
According to recommendations defined by ITU-T (ITU-Telecommunication Standardization Sector), ISDN exchange or switch equipment is equipped with an optional means for feeding power to network termination equipment through a subscriber line. Therefore, there are cases where the ISDN exchange equipment is not equipped with the power feeding means. To supply power from the side of the ISDN exchange equipment without a power feeding facility to the network termination equipment, there has been proposed a system having a power feeding adapter connected between the ISDN exchange equipment and the network termination equipment in Japanese Patent Unexamined Publication No. 8-251819.
More specifically, the ISDN exchange equipment is provided with a plurality of line termination circuits and the network termination equipment is provided with two network termination FQ5-331 2 circuits each corresponding to a different line termination circuit. The power feeding adapter is provided with first and second transformers which connect the two network termination circuits of the network termination equipment and the corresponding line termination circuits of the ISDN exchange equipment through a pair of 2-wire subscriber lines, respectively.
The power feeding adapter is further provided with a DC power source where the one output terminal of the DC power source is connected to the center tap of the secondary winding of the first transformer and the other output terminal of the DC power source is connected to the center tap of the secondary winding of the second transformer. The DC power is transferred to the network termination equipment through the pair of two 2-wire subscriber lines.
According to the above conventional system, however, a problem comes up in association with a subscriber line test which is an important function of the line termination circuit or subscriber line interface circuit. The subscriber line test is performed to measure various physical quantities including line resistance and capacitance between subscriber lines in a state where the subscriber line interface circuits are directly connected to the subscriber lines.
Therefore, in the case of the above conventional system, it is necessary to isolate the power feeding adapter from the subscriber lines when the subscriber line test is started and to connect it to the subscriber lines again when the subscriber line test has been completed. To achieve such a switching operation, the power feeding adapter needs to receive test starting and test completion signals from the exchange or switch equipment. However, such test starting and test completion signals are not provided in the case of the exchange equipment without a power feeding facility. In other words, to perform the subscriber line test, each subscriber line interface circuit needs to be provided with an additional circuit for generating the test starting and test completion signals, resulting in increased amount of hardware and complicated circuit configuration.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a power feeding system and method which can perform the subscriber line test using existing exchange equipment without the need of additional circuits other than power feeding equipment.
According to the present invention, a power feeding system for feeding direct-current (DC) power to a subscriber terminal using a pair of 2-wire subscriber lines of exchange equipment, is comprised of a detector for detecting an operation state of each of the pair of 2-wire subscriber lines connected to the exchange equipment and a power supply circuit for supplying the DC power to the subscriber terminal through the pair of 2-wire subscriber lines connected to the subscriber terminal. When the detector detects that the operation state is a subscriber line test state, a switch circuit detaches the power supply from the pair of 2-wire subscriber lines and directly connects the exchange equipment to the subscriber terminal through the pair of 2-wire subscriber lines.
The detector may detect a voltage 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. Alternatively, the detector may 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.
As described above, when the subscriber line test state is detected, the power supply circuit is detached from the subscriber lines and the exchange equipment is directly connected to the subscriber terminal through the subscriber lines. Therefore, the subscriber line test can be easily and automatically performed. After the subscriber line test has been completed, the detector detects a normal communication state and the power supply circuit restarts supplying the DC power to the subscriber terminal through the subscriber lines.


REFERENCES:
patent: 5175764 (1992-12-01), Patel et al.
patent: 5420886 (1995-05-01), Ohmori
patent: 5442697 (1995-08-01), McGary et al.
patent: 5544243 (1996-08-01), Papadopoulos
patent: 5661776 (1997-08-01), Charland
patent: 5832058 (1998-11-01), Walance et al.
patent: 5848127 (1998-12-01), Levitan et al.
patent: 03272254 (1991-12-01), None
patent: 8-251819 (1996-09-01), None

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