U.S. patent application number 13/567788 was filed with the patent office on 2012-11-29 for providing power to powered device having multiple power supply inputs.
Invention is credited to Jeffrey Lynn HEATH, Ryan Charles Huff, John Arthur Stineman, Kirk Tzukai Su.
Application Number | 20120303981 13/567788 |
Document ID | / |
Family ID | 44060365 |
Filed Date | 2012-11-29 |
United States Patent
Application |
20120303981 |
Kind Code |
A1 |
HEATH; Jeffrey Lynn ; et
al. |
November 29, 2012 |
Providing power to powered device having multiple power supply
inputs
Abstract
A system for providing power to a load, having first and second
power supply inputs respectively responsive to first and second
input signals from first and second power supply sources to supply
power to the load. For example, the first power supply input may be
configured for supplying the load with power received from a
communication link, such as an Ethernet link, and the second power
supply input may be configured for supplying the load with power
from an auxiliary power source. A power converter is provided to
produce an output signal for supplying power to the load in
response to the second input signal. The power converter is
controlled to produce the output signal in accordance with a value
of the first input signal.
Inventors: |
HEATH; Jeffrey Lynn; (Santa
Barbara, CA) ; Stineman; John Arthur; (Carpinteria,
CA) ; Huff; Ryan Charles; (Santa Barbara, CA)
; Su; Kirk Tzukai; (Santa Barbara, CA) |
Family ID: |
44060365 |
Appl. No.: |
13/567788 |
Filed: |
August 6, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12759270 |
Apr 13, 2010 |
|
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13567788 |
|
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61263628 |
Nov 23, 2009 |
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Current U.S.
Class: |
713/300 |
Current CPC
Class: |
H02J 1/108 20130101;
H04L 12/10 20130101 |
Class at
Publication: |
713/300 |
International
Class: |
G06F 1/26 20060101
G06F001/26 |
Claims
1. A system for providing power to a load comprising: a first power
supply input responsive to a first input signal from a first power
supply source to supply power to the load, and a second power
supply input responsive to a second input signal from a second
power supply source to supply power to the load, a power converter
responsive to the second input signal to produce an output signal
for supplying power to the load, the power converter being
controlled to produce the output signal in accordance with a value
of the first input signal.
2. The system of claim 1, wherein the power converter is controlled
to produce the output signal so as to make a difference between a
value of the output signal and the value of the first input signal
smaller than a difference between a value of the second input
signal and the value of the first input signal.
3. The system of claim 1, further comprising a priority mechanism
for enabling a user to select between supplying the load from the
first power supply input and supplying the load from the second
power supply input when both the first and second power supply
inputs are provided with power values sufficient to power the
load.
4. The system of claim 3, wherein the priority mechanism includes a
converter control circuit responsive to a priority select signal
for producing a converter control signal for controlling the power
converter so as to power the load from a power supply input
selected between the first and the second power supply inputs when
both the first and second power supply inputs are provided with
power values sufficient to power the load.
5. The system of claim 4, wherein the power converter is responsive
to the converter control signal to produce the output signal at a
level selected to enable the selected power supply input to provide
power to the load and to prevent a non-selected power supply input
from supplying power to the load.
6. The system of claim 4, wherein the power converter is responsive
to the converter control signal to produce the output signal having
a value lower than a value of the first power supply signal if the
first power supply input is selected to power the load, and to
produce the output signal having a value higher than the value of
the first power supply signal if the second power supply input is
selected to power the load.
7. The system of claim 3, wherein the priority mechanism is
configured to enable the user to change a priority of one power
supply input over another power supply input when both power supply
inputs are provided with power values sufficient to power the
load.
8. The system of claim 1, further comprising a power supply sensing
mechanism for sensing the second input signal at the second power
supply input so as to enable the power converter to operate as a
DC/DC converter when the second input signal is a DC signal and to
operate as an AC/DC converter when the second input signal is an AC
signal.
9. The system of claim 1, wherein the first power supply input is
configured for supplying the load with power received from an
Ethernet link, and the second power supply input is configured for
supplying the load with power from an auxiliary power source.
10-31. (canceled)
32. A method of providing power to a powered device from first and
second power supply inputs, including the steps of: converting a
first power supply signal from a first power supply input to
produce an output signal having a first value selected to power the
powered device from the first power supply input and to prevent the
second power supply input from powering the powered device, and
converting the first power supply signal from the first power
supply input to produce the output signal having a second value
selected to power the powered device from the second power supply
input and to prevent the first power supply input from powering the
powered device.
33. The method of claim 32, wherein a value of the output signal is
controlled in accordance with a value of a second power supply
signal from the second power supply input.
34. The method of claim 32, further comprising the step of
controlling the output signal so as to switch power supply of the
powered device between the first power supply input and the second
power supply input without disrupting power supplied to the powered
device.
35. The method of claim 32, further comprising the step of
controlling the output signal so as to select either the first
power supply input or the second power supply input for powering
the powered device when both the first power supply input and the
second power supply input are available to provide sufficient power
to power the powered device.
Description
[0001] This application claims priority of and incorporates by
reference provisional U.S. patent application Ser. No. 61/263,628
filed on Nov. 23, 2009, and entitled "POWERED DEVICE PROVIDING
SEAMLESS SWITCHING BETWEEN POWER SUPPLY INPUTS."
TECHNICAL FIELD
[0002] This disclosure relates to power supply systems, and more
particularly, to providing power to a powered device having
multiple power supply inputs, such as a Powered Device (PD) in a
Power over Ethernet (PoE) system or a Power over Ethernet Plus
(PoE+) system, capable of receiving power from the Ethernet and
from auxiliary power supplies.
BACKGROUND ART
[0003] Over the years, the Ethernet has become the most commonly
used method for local area networking. PoE and PoE+ systems provide
power delivery over unshielded twisted-pair wiring from Power
Sourcing Equipment (PSE) to a PD located at opposite sides of the
Ethernet link. Powered Devices (PDs) may include such network
devices as IP phones, wireless LAN access points, personal
computers, Web and security cameras, etc. The PoE/PoE+ system
supports providing power to PDs over Ethernet cabling used for data
transmission.
[0004] The PoE system is defined in the IEEE 802.3af standard, and
the PoE+ system is described in the IEEE 802.3at draft standard.
PSE and PD are non-data entities allowing network devices to supply
and draw power using the same generic cabling as is used for data
transmission. A PSE is the equipment electrically specified at the
point of the physical connection to the cabling, that provides the
power to a link. A PSE is typically associated with an Ethernet
switch, router, hub or other network switching equipment or midspan
device.
[0005] PSE searches the link for a PD requesting power, optionally
classifies the PD, supplies power to the link if a PD is detected,
monitors the power on the link, and disconnects power when it is no
longer requested or required. PD participates in the PD detection
procedure by presenting a PoE detection signature defined in the
IEEE 802.3af standard and/or the IEEE 802.3at standard (referred to
below as "IEEE 802.3af/IEEE 802.3at standard"). If the detection
signature is valid, the PD has an option of presenting to the PSE a
class signature defined in the IEEE 802.3af/IEEE 802.3at standard,
to indicate how much power it will draw when powered up. Based on
the determined class of the PD, the PSE applies the required power
to the PD.
[0006] In addition to a PoE/PoE+ power supply input coupled to an
Ethernet link, the PD may have one or more auxiliary power supply
inputs for receiving power from auxiliary power supply sources to
support operation of the PD when the power from the PSE is not
available.
[0007] Therefore, it would be desirable to develop efficient and
cost-effective circuitry that would enable a PD to receive power
from the PoE/PoE+ power supply input and from the auxiliary power
supply inputs, and provide seamless switching among various power
supply inputs.
SUMMARY OF THE DISCLOSURE
[0008] In accordance with one aspect of the disclosure, a system
for providing power to a load comprises first and second power
supply inputs respectively responsive to first and second input
signals from first and second power supply sources to supply power
to the load. For example, the first power supply input may be
configured for supplying the load with power received from a
communication link, such as an Ethernet link, and the second power
supply input may be configured for supplying the load with power
from an auxiliary power source. A power converter is provided to
produce an output signal for supplying power to the load in
response to the second input signal. The power converter is
controlled to produce the output signal in accordance with a value
of the first input signal.
[0009] In particular, the power converter may be controlled to
produce the output signal so as to make a difference between a
value of the output signal and the value of the first input signal
smaller than a difference between a value of the second input
signal and the value of the first input signal.
[0010] The system may comprise a priority mechanism for enabling a
user to select between supplying the load from the first power
supply input or from the second power supply input when both power
supply inputs are provided with power values sufficient to power
the load.
[0011] The priority mechanism may include a converter control
circuit responsive to a priority select signal for producing a
converter control signal that controls the power converter so as to
power the load from the selected power supply input when both power
supply inputs are provided with power values sufficient to power
the load.
[0012] In response to the converter control signal, the power
converter may produce the output signal at a level selected to
enable the selected power supply input to provide power to the load
and to prevent a non-selected power supply input from supplying
power to the load.
[0013] For example, in response to the converter control signal,
the power converter may produce the output signal having a value
lower than a value of the first power supply signal if the first
power supply input is selected to power the load, and to produce
the output signal having a value higher than the value of the first
power supply signal if the second power supply input is selected to
power the load.
[0014] The priority mechanism may be configured to enable the user
to change a priority of one power supply input over another power
supply input when both power supply inputs are provided with power
values sufficient to power the load.
[0015] A power supply sensing mechanism may be provided for sensing
the second input signal at the second power supply input so as to
enable the power converter to operate as a DC/DC converter when the
second input signal is a DC signal and to operate as an AC/DC
converter when the second input signal is an AC signal.
[0016] In accordance with another aspect of the disclosure, a
system for providing power to a powered device comprises a
communication link power supply path responsive to a first power
supply signal received from a communication link, for powering the
powered device, and an auxiliary power supply path responsive to a
second power supply signal from an auxiliary power source, for
powering the powered device. For example, the communication link
power supply path may be configured to supply the powered device
with power received from an Ethernet link in accordance with Power
over Ethernet (PoE) requirements. The power converter may have an
input responsive to a power supply signal from the auxiliary power
source, and an output to produce a converter output signal for
providing power from the auxiliary power source to the powered
device.
[0017] A control circuit is provided to control the power converter
so as to provide power supply switching between the communication
link power supply path and the auxiliary power supply path. In
particular, the control circuit may control the power converter so
as to initiate supplying the powered device from the communication
link power supply path when the powered device is provided with
power from the auxiliary power supply path, and to initiate
supplying the powered device from the auxiliary power supply path
when the powered device is provided with power from the
communication link power supply path.
[0018] The control circuit may be configured to provide power
supply switching between the communication link power supply path
and the auxiliary power supply path without disrupting power supply
of the powered device.
[0019] The power converter may be controlled to produce the
converter output signal at a first level that enables the
communication link power supply path to power the powered device,
and to produce the converter output signal at a second level that
enables the auxiliary power supply path to power the powered
device.
[0020] In particular, the power converter may be controlled to
produce an output voltage value lower that a voltage value from the
communication link power supply path in order to enable the
communication link power supply path to power the powered device,
and to produce the output voltage value greater that the voltage
value from the communication link power supply path in order to
enable the auxiliary power supply path to power the powered
device
[0021] In accordance with an exemplary embodiment of the
disclosure, the power converter may be controlled to produce the
converter output signal at a level selected to electrically isolate
the communication link power supply path from the auxiliary power
supply path.
[0022] Also, the power converter may be controlled to produce the
converter output signal at a level selected to enable the
communication link power supply path to receive power from the
communication link when the auxiliary power supply path provides
powering of the powered device.
[0023] In particular, the communication link power supply path may
be configured for producing a detection signature required to
detect the powered device, when the auxiliary power supply path
provides powering of the powered device. The power converter may be
controlled to produce the converter output signal at a level
selected to prevent the detection signature from being corrupted by
the auxiliary power supply path.
[0024] Also, the communication link power supply path may be
configured for drawing the minimum amount of current required to
maintain power supply from the communication link, when the
auxiliary power supply path provides powering of the powered
device.
[0025] The control circuit may be configured to enable a user to
select between powering the powered device from the communication
link or from the auxiliary power source when sufficient power from
both the communication link power supply path and the auxiliary
power supply path is available for powering the powered device. The
control circuit may control the power converter so as to power the
powered device in accordance with user's selection.
[0026] A diode bridge may be provided at an input of the auxiliary
power supply path to receive a power supply signal from the
auxiliary power source. Alternatively, a transistor bridge
including first and second pairs of transistors may be provided at
the input of the auxiliary power supply path to receive the power
supply signal.
[0027] A polarity detector may be provided to sense polarities of
the signals at the input and output of the transistor bridge so as
to set the first pair of transistors in an on state and the second
pair of transistors in an off state when a polarity of a signal at
an input of the transistor bridge coincides with a polarity of a
signal at an output of the transistor bridge, and to set the second
pair of transistors in an on state and the first pair of
transistors in an off state when a polarity of the signal at the
input of the transistor bridge does not coincide with a polarity of
the signal at the output of the transistor bridge.
[0028] The system may further include first and second output diode
components, wherein the first output diode component may be
controlled to enable the communication link power supply path to
power the powered device and prevent the auxiliary power supply
path from powering the powered device, and the second output diode
component may be controlled to enable the auxiliary power supply
path to power the powered device and prevent the communication link
power supply path from powering the powered device.
[0029] Alternatively, first and second output transistor components
may be provided, wherein the first output transistor component may
be controlled to enable the communication link power supply path to
power the powered device and prevent the auxiliary power supply
path from powering the powered device, and the second output
transistor component may be controlled to enable the auxiliary
power supply path to power the powered device and prevent the
communication link power supply path from powering the powered
device.
[0030] The control circuit may be configured to control the power
converter in accordance with a difference between an output voltage
of the power converter and a voltage at a node between the first
output transistor component and the second output transistor
component.
[0031] In accordance with a further aspect of the disclosure, the
power converter may be configured to perform power factor
correction.
[0032] In accordance with an embodiment of the disclosure, the
communication link power supply path may be configured to receive
PoE+ power from the Ethernet link provided in accordance with IEEE
802.3at standard. In particular, the communication link power
supply path may be configured to detect the PoE+ power based on
2-Event Physical Layer classification. Alternatively, the
communication link power supply path may detect the PoE+ power
based on Data Link Layer classification.
[0033] In accordance with a method of the present disclosure, the
following steps may be carried out to provide power to a powered
device from first and second power supply inputs: [0034] converting
a first power supply signal from a first power supply input to
produce an output signal having a first value selected to power the
powered device from the first power supply input and to prevent the
second power supply input from powering the powered device, and
[0035] converting the first power supply signal from the first
power supply input to produce the output signal having a second
value selected to power the powered device from the second power
supply input and to prevent the first power supply input from
powering the powered device.
[0036] A value of the output signal may be controlled in accordance
with a value of a second power supply signal from the second power
supply input so as to reduce a difference between the value of the
output signal and a value of the second power supply signal with
respect to a difference between a value of the first power supply
signal and the value of the second power supply signal.
[0037] The output signal may be controlled so as to switch power
supply of the powered device between the first power supply input
and the second power supply input without disrupting power supplied
to the powered device.
[0038] Also, the output signal may be controlled so as to select
either the first power supply input or the second power supply
input for powering the powered device when both the first power
supply input and the second power supply input are available to
provide sufficient power to power the powered device.
[0039] Additional advantages and aspects of the disclosure will
become readily apparent to those skilled in the art from the
following detailed description, wherein embodiments of the present
disclosure are shown and described, simply by way of illustration
of the best mode contemplated for practicing the present
disclosure. As will be described, the disclosure is capable of
other and different embodiments, and its several details are
susceptible of modification in various obvious respects, all
without departing from the spirit of the disclosure. Accordingly,
the drawings and description are to be regarded as illustrative in
nature, and not as limitative.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The drawing figures depict concepts by way of example, not
by way of limitations. In the figures, like reference numerals
refer to the same or similar elements.
[0041] FIG. 1 is a diagram illustrating a general concept of a
system for providing power to a load using multiple power supply
inputs in accordance with the present disclosure.
[0042] FIG. 2 is a diagram illustrating an exemplary embodiment of
a system for supplying power to a powered device using PoE/PoE+
power supply input coupled to an Ethernet link and at least one
auxiliary power supply input for providing power from an auxiliary
power source.
[0043] FIG. 3 is a diagram illustrating exemplary embodiments of
diode and transistor bridges that may be arranged for receiving
power from the auxiliary power source.
[0044] FIG. 4 is a diagram illustrating an exemplary embodiment of
a power supply system having output transistor devices controlled
to provide power from multiple power supply inputs to the powered
device.
[0045] FIG. 5 is a diagram illustrating exemplary operation of a
control circuit in the power supply system.
[0046] FIG. 6 is a diagram illustrating an exemplary embodiment of
a power supply system configured to support PoE+ power supply and
auxiliary power supply.
DETAILED DISCLOSURE OF THE EMBODIMENTS
[0047] The present disclosure will be made with examples of a
powered device (PD) in a PoE and/or PoE+ (referred to below as
PoE/PoE+) environment. It will become apparent, however, that the
concepts described herein are applicable to providing power to any
powered device using multiple power supply inputs.
[0048] FIG. 1 illustrates a general concept of a system 10 that
provides power to a load 12 and has a pair of power supply inputs
for supplying input voltages V1 and V2. For example, input voltages
V1 and V2 may be DC voltages. However, as discussed in more detail
below, one of input voltages, for example, voltage V2 may be AC
voltage.
[0049] The voltage V1 is supplied to the load via a first power
supply channel, whereas the voltage V2 is supplied to the load via
a second power supply channel having a power converter 14, such as
DC/DC or AC/DC converter, that may convert the voltage V2 so as to
provide balancing between the voltage supplied to the load 12 from
the first power supply channel and the voltage supplied to the load
12 from the second power supply channel. The power converter 14 may
be controlled in accordance with the voltage value V1 so as to
convert the voltage value V2 into a desired output voltage value
V2out. For example, the power converter 14 may be controlled to
reduce a difference between V1 and V2out with respect to a
difference between V1 and V2. Hence, the power converter 14 reduces
the design burden on the load circuitry 12 by decreasing the
voltage range in which the load 12 must operate. Voltages V1 and
V2out may be respectively supplied to the load 12 via
unidirectional conduction devices, such as diodes 16 and 18.
[0050] In accordance with one aspect of the disclosure, a priority
mechanism may be provided to enable the user to select which power
supply channel should provide power to the load 12 when both
voltages V1 and V2 are sufficient to power the load 12. The
priority mechanism may include a control circuit 20 supplied with a
priority select signal to produce a converter control signal that
controls the power converter 14. The priority select signal may be
defined by the user to set a priority of one power supply channel
over the other power supply channel.
[0051] For example, if the priority select signal is asserted to
establish priority of the first power supply channel over the
second power supply channel, the control circuit 20 may adjust the
power converter 14 so as to produce the voltage value V2out at the
output of the converter 14 lower than the voltage V1. As a result,
the output voltage of the first power supply channel will be
provided to the load 12, and the output voltage of the second power
supply channel will be prevented by the diode 18 from being
supplied to the load 12.
[0052] By contrast, if the priority select signal is asserted to
establish priority of the second power supply channel over the
first power supply channel, the control circuit 20 may adjust the
power converter 14 so as to produce the voltage value V2out at the
output of the converter 14 higher than the voltage V1. As a result,
the output voltage of the second power supply channel will be
provided to the load 12, and the output voltage of the first power
supply channel will be prevented by the diode 16 from being
supplied to the load 12.
[0053] The priority mechanism of the present disclosure provides
seamless switching between the power supply inputs V1 and V2
without disrupting the voltage being supplied to the load 12. The
priority can be set and dynamically changed by asserting the
priority select signal in accordance with the user's requirements.
For example, the priority select signal may be asserted at a first
logic level to provide priority of the first power supply channel
over the second power supply channel, and the priority select
signal may be asserted at a second logic level to provide priority
of the second power supply channel over the first power supply
channel. As one skilled in the art would realize, the priority
mechanism of the present disclosure can be utilized to establish
priority of any one power supply channel or any group of power
supply channels over another power supply channel or another group
of power supply channels.
[0054] The second power supply channel may operate with either DC
voltage or AC voltage provided at its input. A DC sensing circuit
22 may be arranged at the input of the second power supply channel
to determine whether AC voltage or DC voltage is provided. If the
DC voltage is sensed at the input of the second power supply
channel, the DC sensing circuit 22 controls the power converter 14
to operate in a DC-to-DC voltage conversion mode. If no DC voltage
is sensed, the DC sensing circuit 22 controls the power converter
14 to operate in an AC-to-DC voltage conversion mode.
[0055] FIG. 2 illustrates an exemplary system 100 for providing
power to a powered device (PD) in a PoE/PoE+ environment. The
system 100 provides power to a power converter 102, such as a DC/DC
converter, that generates a power output required by the PD, which
is connectable to the power converter 102. The system 100 includes
a PoE/PoE+ power supply channel 104 for providing PoE/PoE+ power
supply input from the Ethernet cabling in accordance with PoE or
PoE+ requirements respectively described in the WEE 802.3af
standard or the IEEE 802.3at draft standard. An eight-wire Ethernet
connector, such as a Registered Jack-45 (RJ-45) connector, may be
used for providing electrical connection to the Ethernet cabling.
As described in the IEEE 802.3af/IEEE 802.3at standard, the
Ethernet connector may be connected to data communication circuitry
that may include magnetic components and associated circuitry
required for supporting Ethernet data communications protocols,
such as 10BASE-T, 100BASE-T, 100BASE-TX and/or 1000BASE-T,
performed to provide data communication over the Ethernet network.
Also, the system may include an auxiliary power supply channel 106
for providing power from an auxiliary AC or DC power source such as
a wall transformer.
[0056] The PoE/PoE+ power supply channel 104 may include an input
diode bridge circuit 108 that may be connected to the magnetic
components of the Ethernet data communication circuitry to enable
the PD to accept voltages of any polarity when power is supplied
over the Ethernet link. Further, the PoE/PoE+ power supply channel
104 includes PD interfacing and switching circuitry 110 that
performs operations prescribed by the IEEE 802.3af/IEEE 802.3at
standard in order to deliver power from the respective Power
Sourcing Equipment (PSE) to the PD.
[0057] In particular, when the PSE performs a detection procedure
to detect whether the PD is a valid PD that may be provided with
PoE/PoE+ power, the interfacing and switching circuitry 110
presents a valid detection signature required from the PD. For
example, the detection signature may be a 25K signature resistor.
When the PSE applies a proper detection voltage on the Ethernet
cabling, the interfacing and switching circuitry 110 may connect
the signature resistance to the PoE/PoE+ input so as to enable the
PSE to detect it.
[0058] After presenting the valid detection signature, the PD has
an option of presenting a class signature to the PSE to indicate
how much power it will draw when powered up. For example, a PD may
be classified as class 0 to class 4. Based on the determined class
of the PD, the PSE applies the required power to the PD over the
Ethernet link. The interfacing and switching circuitry 110 supports
the PD operation by presenting a class signature that indicates a
power requirement of the PD. For example, the class signature may
be presented in a form of classification current asserted by the
interfacing and switching circuitry 110 in response to a prescribed
value of classification voltage applied by the PSE.
[0059] When the PoE/PoE+ power is provided in accordance with the
IEEE 802.3af/IEEE 802.3at procedure, the interfacing and switching
circuit 110 may produce a power good signal indicating that the
PoE/PoE+ power supply is available and ready. Also, when the power
up procedure prescribed by the IEEE 802.3af/IEEE 802.3at is
completed, a switch in the interfacing and switching circuit 110
may be set into an on state to supply the PoE/PoE+ power to the
converter 102.
[0060] In accordance with the IEEE 802.3af/IEEE 802.3at standard,
the PSE uses the maintain power signature (MPS) operation to
determine if a PD continues to require power after the power was
provided to the PD. The MPS requires the PD to periodically draw at
least 10 mA. The PoE/PoE+ power supply channel 104 may include a
minimum load current circuit 112 that provides the load current
required to satisfy the MPS requirement. The minimum load current
circuit 112 may include an MPS current source for providing the
load current required to satisfy the MPS requirements, and an MPS
control switch controlled by an MPS control signal to enable the
current supply from the MPS current source at a time period when
the MPS is required in accordance with the IEEE 802.3af/IEEE
802.3at standard. To reduce the average power dissipation, the MPS
control signal may be a periodic signal that turns the MPS control
switch on and off periodically.
[0061] The auxiliary power supply channel 106 may include an input
diode bridge circuit 114 connected to the auxiliary power source so
as to accept voltages of any polarity when power is supplied from
the auxiliary power source. As discussed below, the input diode
bridge circuit may be replaced with a MOSFET bridge circuit to
reduce power loss on the input bridge circuit.
[0062] Further, the auxiliary power supply channel 106 may include
a power converter 116, such as a DC/DC or AC/DC converter, for
converting the input voltage applied from the auxiliary power
supply source so as to provide balancing between the voltage
supplied to the power converter 102 from the PoE/PoE+ power supply
channel 104 and the voltage supplied to the power converter 102
from the auxiliary power supply channel 106. For example, the power
converter 116 may convert the voltage from the auxiliary power
supply into a value that is closer to the voltage supplied from the
Ethernet link, in order to reduce the difference between these
voltages. Voltage from the PoE/PoE+ power supply channel 104 and
the output voltage of the power converter 116 may be respectively
supplied to the DC/DC converter 102 via unidirectional conduction
devices, such as diodes 118 and 120.
[0063] In a purely resistive AC circuit, voltage and current
waveforms are in step (or in phase), changing polarity at the same
instant in each cycle. If reactive loads are present, energy
storage in the loads result in a time difference between the
current and voltage waveforms. Circuits containing purely resistive
elements have a power factor of 1.0. Circuits containing inductive
or capacitive elements often have a power factor below 1.0. A
circuit with a lower power factor will use higher currents to
transfer a given quantity of real power than a circuit with a
higher power factor.
[0064] Therefore, the AC/DC power converter 116 may be configured
to perform power factor correction, i.e. to adjust the power factor
of the circuit to near 1.0, to reduce the reactive power loss. In
particular, the power converter 116 performs power factor
correction by aligning the load current of the power converter 116
in phase with the AC voltage so that the auxiliary power input 106
appears purely resistive and the reactive power loss is
reduced.
[0065] The system 100 further includes a control circuit 122 that
controls the power converter 116 and the minimum load current
circuit 112 to provide seamless switching between the PoE/PoE power
supply input and the auxiliary power supply input.
[0066] In particular, the control circuit 122 may support a
priority mechanism provided to enable the user to select whether
the PoE/PoE+ power supply or the auxiliary power supply should
provide power to the PD when both the PoE/PoE+ voltage and the
auxiliary power source voltage are sufficient to power the PD. The
control circuit 122 is supplied with a priority select signal to
produce a converter control signal that controls the power
converter 116. The priority select signal may be defined by the
user to set a priority of one power supply channel over the other
power supply channel.
[0067] For example, if the priority select signal is asserted to
establish priority of the PoE/PoE+ power supply over the auxiliary
power supply, the control circuit 122 may adjust the power
converter 116 so as to produce the voltage value at the output of
the converter 116 lower than the PoE/PoE+ voltage from the Ethernet
link. As a result, the PoE/PoE+ voltage will be provided to the PD,
and the voltage of the auxiliary power supply channel will be
prevented by the diode 120 from being supplied to the PD.
[0068] By contrast, if the priority select signal is asserted to
establish priority of the auxiliary power supply over the PoE/PoE+
power supply, the control circuit 122 may adjust the power
converter 116 so as to produce the voltage value at the output of
the converter 116 higher than the PoE/PoE+ voltage. As a result,
the output voltage of the auxiliary power supply channel will be
provided to the PD, and the PoE/PoE+ voltage will be prevented by
the diode 118 from being supplied to the PD.
[0069] In conventional PD power supply systems having a PoE power
supply input and an auxiliary power supply input, when a PD is
supplied from an auxiliary power source, PoE power supply from the
Ethernet link is disrupted because the PD no longer draws current
from the Ethernet, and a PSE removes power since the MPS
requirement is not satisfied.
[0070] Moreover, in conventional PD power supply systems, when a PD
is supplied from an auxiliary power source, the PSE cannot perform
the detection procedure prescribed by the PoE/PoE+ standard because
the PD input impedance that serves as the detection signature
resistance becomes corrupted since the input diode bridge 108 is
reverse biased by the auxiliary voltage, which is higher than the
PoE voltage. Therefore, when the auxiliary power supply provided
from the auxiliary power source is removed, the PD must go through
the detection, classification and power-up procedures prescribed by
the PoE/PoE+ standard, in order to resume PoE/PoE+ power supply
from the Ethernet link. As a result, switching from the auxiliary
power supply to the PoE/PoE+ power supply cannot be performed
without disrupting power at the PD.
[0071] In accordance with the present disclosure, the power
converter 116, together with the diode 118, prevents the detection
signature resistance from being corrupted. In particular, when the
power converter 116 produces the output voltage that is higher than
the PoE/PoE+ voltage, the PoE/PoE+ power supply channel is isolated
by the reverse diode 118, which prevents any current from being
added to or subtracted from the PoE/PoE+ power supply channel to
corrupt the detection signature. Hence, even when the PoE/PoE+
power supply to the PD is replaced with the auxiliary power supply,
the PSE is enabled to detect a detection signature presented by the
PoE/PoE+ power supply channel in response to a detection signal
from the PSE.
[0072] Moreover, in accordance with the present disclosure, the
minimum load current circuit 112 enables the PD to maintain the
necessary load current required to satisfy the MPS requirement even
when the PD is powered with the auxiliary power supply instead of
the PoE/PoE+ power supply. The control circuit 122 is configured to
produce the MPS control signal supplied to the minimum load current
circuit 112 to dynamically enable or disable the MPS current supply
from the minimum load current circuit 112.
[0073] When the auxiliary power supply channel 106 is selected to
provide power to the PD, the MPS is required to prevent the
PoE/PoE+ power supply at the input of the PoE/PoE power supply
channel 104 from being disrupted, and to enable the PoE/PoE+ power
supply input to replace the auxiliary power supply input, if
necessary. Hence, the control circuit 122 enables the current
supply from the MPS current source in the minimum load current
circuit 112 when the auxiliary power supply channel 106 powers the
PD and the PoE/PoE+ power supply channel 104 operates in a standby
mode capable of replacing the auxiliary power supply, if
necessary.
[0074] The MPS supply from the MPS current source is disabled
during the PoE/PoE+ powering procedure performed to establish the
PoE/PoE+ power supply at the input of the PoE/PoE+ power supply
channel 104. Also, when the auxiliary power supply is not present
or if the auxiliary power supply is not selected by the priority
select signal, the MPS supply from the minimum load current circuit
112 may be disabled to improve power delivery efficiency from the
PoE/PoE+ power supply input.
[0075] Hence, when both the auxiliary power supply and the PoE/PoE+
power supply are provided at the respective power supply inputs,
the control circuit 122 responds to the priority select signal by
supplying the power converter 116 with the converter control signal
to set the output voltage of the converter 116 above or below the
voltage applied at the input of the PoE/PoE+ power supply channel
104. If the priority is selected to establish the auxiliary power
supply of the PD, the power converter 116 is controlled to maintain
its output voltage above the PoE/PoE+ voltage.
[0076] When the priority is selected to set the PoE/PoE+ power
supply of the PD, the control circuit 122 determines whether the
power good signal is provided from the interfacing and switching
circuit 110. If the power good signal is detected, the control
circuit 122 controls the power converter 116 to provide the output
voltage at a level below the PoE/PoE+ voltage so as to enable the
PoE/PoE+ channel 104 to supply power to the converter 102 and the
PD.
[0077] As discussed above, switching between the PoE/PoE+ power
supply input and the auxiliary power supply input is provided
seamlessly without disruption of the voltage being supplied to the
PD. Also, the selected priority of one power supply channel over
another power supply channel may be changed dynamically by
adjusting the voltage at the output of the converter 116.
[0078] As illustrated in FIGS. 3 and 4, diodes in the system 100 in
FIG. 2 may be replaced with transistors, such as MOSFETs, so as to
improve efficiency of power delivery from the power supply inputs
to the converter 102. Power loss due to the power dissipation on
the diodes is particularly undesirable at the input of the
auxiliary power supply channel 106 employing the diode bridge 114.
For example, when the auxiliary power supply is provided from an
(12.+-.10%)V DC power source, additional voltage drops on two
diodes reduces the line voltage to as low as 9.5V, reducing power
delivery efficiency by 12%. In cases where power deliver efficiency
is important, the diodes in the diode bridge 114 may be replaced
with MOSFETs to reduce the power dissipation on the bridge to a
small fraction of the power dissipation on the diode bridge.
[0079] FIG. 3 shows the diode bridge 114 with diodes 132, 134, 136
and 138 that may be replaced by a MOSFET bridge 140 with MOSFETs
142, 144, 146 and 148, The polarity of the input voltage Vin
supplied to the bridge 114 or the bridge 140 from the auxiliary
power source is unknown. Control circuitry 150 may be connected to
the MOSFET bridge 140 to control the MOSFET bridge 140 so as to
provide output voltage Vout appropriate for supplying to the input
of the power converter 116. If a voltage is provided to drive the
gate voltages of the MOSFETs above the high rail voltage, NMOS
transistors may be selected as all MOSFETs 142-148. Alternatively,
the bridge 140 may include a pair of NMOS transistors and a pair of
PMOS transistors.
[0080] The control circuitry 150 may include a comparison circuit
152 that determines whether or not the voltages Vin and Vout are of
the same polarity or have opposite polarities. For example, if the
voltages Vin and Vout are of the same polarity, the comparison
circuit 152 supplies gate control signals to gates of the MOSFETs
144 and 148 so as to place the MOSFETs 144 and 148 into an on
state, while the MOSFETs 142 and 146 remains in an off state.
Alternatively, if the voltages Vin and Vout have opposite
polarities, the comparison circuit 152 supplies gate control
signals to gates of the MOSFETs 142 and 146 so as to turn on these
MOSFETs, while the MOSFETs 144 and 148 remains in the off
state.
[0081] The system 100 in FIG. 2 may be arranged so as employ
MOSFETs 142-148 in a MOSFET mode when the auxiliary power source is
a DC voltage source, such as a 12V DC source, and to operate
MOSFETs 142-148 in a diode mode when the auxiliary power source is
an AC voltage source, such as 24V AC source. The control circuitry
150 may be provided with a DC sensing circuit 154 that enables the
comparison circuit 152 to turn on the appropriate pair of the
MOSFETs only when the DC voltage is detected at the input of the
auxiliary power supply channel 106. When no DC voltage is detected,
the DC sensing circuit 154 disables the comparison circuit 152 to
allow the MOSFETs 142-148 to operate in a diode mode as MOSFET body
diodes.
[0082] The diode bridge 108 at the input of the PoE/PoE+ power
supply channel also may be replaced with a MOSFET bridge to improve
efficiency of power delivery from the PoE/PoE+ power supply input
to the output of the converter 102.
[0083] FIG. 4 shows the system in FIG. 2 in which the diodes 118
and 120 in FIG. 2 are replaced with MOSFETs 158 and 160 to improve
power delivery efficiency. In particular, the diodes 118 and 120
cause power dissipation due to the voltage developed across a
forward conducting diode. The MOSFETs 158 and 160 reduce this
voltage to a value equal to the on resistance of the MOSFET
multiplied by the operating current value, thus reducing the power
dissipation.
[0084] For example, the MOSFETs 158 and 160 may be controlled by
the control circuit 122 that produces gate control signals supplied
to gates of the MOSFETs 158 and 160 to turn on one of them and to
turn off the other. As illustrated in FIG. 5, the control circuit
122 may include a logic circuit 162 that analyses the priority
select signal and the power good signal to determine whether the
PoE/PoE+ power supply channel 104 or the auxiliary channel 106 will
provide power to the converter 102. If the logic circuit 162
determines that the PoE/PoE+ power supply channel 104 is selected
to provide power to the converter 102 and is ready to supply
PoE/PoE+ power, the logic circuit 162 may control a gate driver 164
to provide the gate control signal that turn on the MOSFET 158 and
may control a gate driver 166 to provide a gate control signal that
turns off the MOSFET 160. If the logic circuit determines that the
auxiliary power supply channel 106 will provide power to the
converter 102, the control circuit 122 may control the gate drivers
166 and 164 to supply the gate control signals that respectively
turn on the MOSFET 160 and turn off the MOSFET 158.
[0085] The gate drivers 164 and 166 may be controlled to provide
the gate control signals that turn off both of the MOSFETs 158 and
160. In this case, the MOSFETs 158 and 160 will operate in a diode
mode to perform diode OR function at the node between the MOSFETs
158 and 160.
[0086] Also, the control circuit 122 may include an error amplifier
168 having a first input that senses the voltage at the node 159
between the MOSFETs 158 and 160. The second input of the error
amplifier 168 may be provided with the voltage produced at the
output of the power converter 116. The output signal of the error
amplifier 168 is supplied to a control input of the power converter
116 to control its output voltage. This configuration enables the
control circuit 122 to dynamically track and sense the voltage at
the node 159 so as to set the output voltage of the power converter
116 slightly below the voltage at the node 159 when the PoE/PoE+
channel 104 provides power to the converter 102 while the auxiliary
power is available at the input of the auxiliary channel 106. When
the PoE/PoE+ power is removed or suddenly disrupted, switching from
the PoE/PoE+ power supply of the PD to the auxiliary power supply
is accelerated because the power converter 116 has to respond only
to the difference between the output voltage of the converter 116
and the voltage at the node 159 produced before the PoE power
removal, and to recover its output voltage in response to this
difference.
[0087] FIG. 6 illustrates an exemplary system 200 configured to
comply with specific requirements of the IEEE 802.3at standard that
specifies a PoE+ power supply procedure performed by a PSE and a PD
to enable a PD to receive higher amounts of power (up to 25.5 W)
from the Ethernet link. Similarly to the system 100 in FIG. 2, the
system 200 includes a power supply channel 104 for providing power
supply from the Ethernet cabling and an auxiliary power supply
channel 106 for providing power from an auxiliary AC or DC power
source such as a wall transformer. The system 200 operates in the
manner similar to the operation of system 100. However, special
provisions must be taken to handle PoE+ power supply prescribed by
the IEEE 802.3at standard because the PD must first draw no more
than 12.95 W until it recognizes the presence of PoE+ power supply
that enables the PD to draw up to 25.5 W.
[0088] In addition to the power received from the Ethernet cabling,
the power supply channel 104 may receive data carried over the
Ethernet cabling and required to comply with the IEEE 802.3at
standard. The data may be required to recognize presence of PoE+
power supply. Therefore, in addition to the components described in
connection with FIG. 2, the system 200 includes components required
to handle the data. In particular, a power/data separator 202 is
configured at the input of the channel 104 to receive a combined
power/data signal from the Ethernet cabling and to separate the
data from the power. As one skilled in the art would recognize, the
power/data separator 202 may be implemented using a pair of
transformers. The separator 202 forwards the data received from the
Ethernet cabling to a microprocessor 204, whereas the power is
supplied to a input circuit such as the diode bridge circuit
108.
[0089] In accordance with the IEEE 802.3at standard, classification
of PD may be performed using two forms of classification: Physical
Layer classification and Data Link Layer classification. Physical
Layer classification occurs before a PSE supplies power to a PD
when the PSE asserts a voltage onto the PI (power interface between
the PSE and the transmission medium) and the PD responds with a
current representing a limited number of power classifications.
With Data Link Layer classification, the PSE and PD communicate
using the Data Link Layer Protocol after the data link is
established. Subsequent to successful detection of PD, PSEs may
perform classification using at least one of the following: 2-Event
Physical Layer classification; 2-Event Physical Layer
classification and Data Link Layer classification; or 1-Event
Physical Layer classification and Data Link Layer
classification.
[0090] During 2-Event classification, the PSE interacts with the PD
interfacing and switching circuit 110 in accordance with the
procedure prescribed by the IEEE 802.3at standard to classify the
PD twice. In response to the 2-event classification, the PD
interfacing and switching circuit 110 provides a signal to the
control circuit 122 indicating the presence of PoE+ power
supply.
[0091] Alternatively, PoE+ power supply may be declared based on
the Data Link Layer classification. In this case, the
microprocessor 204 recognizes the PoE+ power supply declaration
based on the data received from the separator 202. When the
microprocessor 204 detects the PoE+ power supply, it determines
whether the PD interfacing and switching circuit 110 asserts the
power good signal indicating that it is ready to pass PoE+ power to
the PD. If the power good signal is asserted, the microprocessor
204 supplies a PoE+ present signal to the control circuit 122
indicating the presence of PoE+ power supply. In response, the
control circuit 122 modifies its control signals to take into
account the increased amount of power available at the input of the
power supply channel 104.
[0092] The foregoing description illustrates and describes aspects
of the present invention. Additionally, the disclosure shows and
describes only preferred embodiments, but as aforementioned, it is
to be understood that the invention is capable of use in various
other combinations, modifications, and environments and is capable
of changes or modifications within the scope of the inventive
concept as expressed herein, commensurate with the above teachings,
and/or the skill or knowledge of the relevant art.
[0093] The embodiments described hereinabove are further intended
to explain best modes known of practicing the invention and to
enable others skilled in the art to utilize the invention in such,
or other, embodiments and with the various modifications required
by the particular applications or uses of the invention.
[0094] Accordingly, the description is not intended to limit the
invention to the form disclosed herein. Also, it is intended that
the appended claims be construed to include alternative
embodiments.
* * * * *