Power feed for network devices

Details Power feed for network devices Power feed for network devices

2000-05-02

2001-09-25

Korzuch, William (Department: 2641)

Telephonic communications

Subscriber line or transmission line interface

Power supply

C379S412000, C379S324000, C375S257000, C375S258000, C375S285000, C333S177000

Reexamination Certificate

active

06295356

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a method and apparatus which provide electrical power to ethernet-based telephones over an ethernet wire link.
2. The Background Art
Telephones require electrical power in order to operate. The power can be delivered over the telephone lines or via a separate power connection, typically through a power transformer connected to the electrical power grid. Telephones powered in the latter fashion will be inoperable during a power failure unless provision is made both locally at the telephone and at the PBX or local telephone switch for emergency power to be supplied. While it is normal to provide an uninterruptible power supply to an office's PBX or telephone switch, it is not desirable for cost and other reasons to provide electrical power back up systems to each telephone location. In the past, the power problem was frequently solved by using an 8-wire telephone connection to the telephone switch. With 8 wires there is more than enough capability for analog audio digital and power connections to the telephone switch.
The growth of the Internet and similar local and wide area networks based on Ethernet technology has created a potential market for telephone systems which would connect directly to existing Ethernet connections. The Ethernet protocol, however, does not provide a mechanism for powering such telephones. A typical Ethernet connection to an office location would include a pair of unshielded twisted pair (UTP) lines for a total of four conductors—one pair for transmit, one for receive. The transmit pair is dedicated to send packets of data over the Ethernet connection; the receive pair receives packets of data over the Ethernet connection. Simply placing a DC bias on two or more of these conductors and using the bias to power a local Ethernet telephone is risky because the bias is not part of the Ethernet protocol and might damage Ethernet compliant equipment not designed to handle such a bias.
Turning to
FIGS. 1 and 2
, a prior art scheme for providing power over a single twisted pair connection is shown. In the prior art, system
10
and power supply
11
provides DC power over lines
12
(positive lead) and
14
(negative lead) to a series of ports on the network. Filter capacitor
16
and filter inductors
18
and
20
are preferably provided to insure a clean source of DC power and to avoid AC cross-talk between the network and the power supply. Each port
22
,
24
and
26
of the network is coupled to a twisted pair link
28
,
30
and
32
, respectively, via a transformer,
34
,
36
, and
38
, respectively. Transformer
34
, for example, operates as follows: Data on port
1
(
22
) is applied to the primary
40
of transformer
34
and coupled to a pair of secondary winding
42
,
44
of transformer
34
through transformer core
46
in a conventional manner. One end
48
of secondary winding
42
is connected to twisted pair
28
and the other end
50
of secondary winding
42
is connected to the positive lead
12
of power supply
11
. One end
52
of secondary winding
44
is connected to twisted pair link
28
and the other end
54
of secondary winding
44
is connected to the negative lead
14
of power supply
11
. Leads
50
and
54
are AC-coupled to one another with capacitor
56
as shown. This blocks DC current from flowing and allows a DC bias to be established over the two conductors of twisted pair link
28
while simultaneously allowing the flow of data over the link.
At the telephone end of the twisted-pair link
28
, a similarly structured transformer
58
receives the data signal as well as the DC bias. First primary
60
and second primary
62
are AC-coupled with capacitor
64
so as to be able to couple data signals from twisted-pair link
28
with transformer
58
while holding off a DC bias. The DC bias of twisted-pair link
28
is applied to a power processor
66
and from there provides to local equipment to be powered by the twisted pair system. A typical embodiment of a power processor
66
is shown in FIG.
2
. It comprises a filter
68
, a rectifier
70
, a filter capacitor
72
and a DC-DC converter
74
.
While fit for its intended purpose, the above-described system has some drawbacks which make it a less than ideal choice for an Ethernet environment. For example, each secondary
42
and
44
of transformer
34
and each primary
60
and
62
of transformer
58
will experience a net current flow equal to the total amount of current drawn by the load at the distal end of the twisted-pair link. This current will affect the choice of transformer core size at each end of the link and will affect the choice of wire gauge used for the link.
It would be desirable to provide an improved method and apparatus for powering Ethernet telephones over a 4-wire link. Such a system would be able to take advantage of existing wiring without the need to rewire the premises to install such devices. Furthermore, by providing power over the Ethernet connection, power transformers are not required at the device location, and a central uninterruptible power supply is made possible to provide power to the entire telephone system in case of a power failure.
SUMMARY OF THE INVENTION
An Ethernet device power transmission system provides electrical power to devices such as Ethernet telephones and related equipment over a 4-wire Ethernet connection without any need for rewiring premises having an existing 4-wire Ethernet system. The system eliminates any requirement for local power such as transformers to power such equipment as all power can be provided over the existing Ethernet wiring. A central uninterruptible power supply (UPS) is thereby made possible to provide back-up power to all such equipment. The system includes an input transformer, an output transformer and a pair of twisted pair conductors. The input transformer includes a pair of primaries for connection to a source of Ethernet data. The input transformer also includes a pair of secondaries, each having a center-tap. A first twisted pair conductor is connected across the first secondary, a second twisted pair conductor is connected across the second secondary and a DC-bias is provided between the respective center taps of the first and second secondaries. At the local end, the output transformer includes a first and second center-tapped primary and a first and second secondary for connection to the load device. The first and second primary center taps are connected to a power processor for extraction of DC power.


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