Power control for powered devices in power over ethernet systems

Abstract

A powered device interface includes a supply sensing circuit, a demand sensing circuit, and a control circuit. The supply sensing circuit is configured to sense an amount of power received by the powered device from at least one power sourcing equipment via an Ethernet cable. The demand sensing circuit is configured to sense a power demand requested by the powered device. The control circuit is coupled with the supply sensing circuit and the demand sensing circuit and is configured to cause the power demand requested by the powered device to be reduced when the power demand requested by the powered device exceeds the amount of power allowed to be provided by the power sourcing equipment for the powered device.

Description

Background Technology

[0001] Power over Ethernet (PoE) technology describes the transmission of power and data over Ethernet cabling. A Power Supply Equipment (PSE) provides or supplies power to a Powered Device (PD) via one or more twisted pairs supported by an Ethernet cable. The twisted pairs can transmit power, data, or both from the PSE to the PD. As the capabilities of powered devices increase, their power requirements typically also increase, in which case more twisted pairs are used to transmit the power. Examples of powered devices include wireless access points, Internet Protocol (IP) phones, IP cameras, retail displays, outdoor units (ODUs), and network routers. Attached Figure Description

[0002] Specific embodiments are described with reference to the accompanying drawings. The same reference numerals are used in different contexts in the specification and drawings to indicate similar or identical items. Various embodiments or examples (“Examples”) of this disclosure are disclosed in the following detailed description and the accompanying drawings. The drawings are not necessarily drawn to scale. Generally, unless otherwise provided in the claims, the disclosed processes can be performed in any order.

[0003] Figure 1 This is a block diagram representation of an example of a Power over Ethernet (PoE) system including an embodiment of a powered device interface of a powered device;

[0004] Figure 2 This is a block diagram representation of an example of a PoE system including an electrical receiver interface of an electrical receiver;

[0005] Figure 3 This is a block diagram representation of an example of a PoE system including an electrical receiver interface of an electrical receiver;

[0006] Figure 4 This is a graph showing the output voltage versus output current of the power received by the powered device from the power supply equipment (PSE) in a PoE system, in the case of an embodiment where power control is performed via the powered device interface.

[0007] Figure 5A These are block diagrams and circuit diagrams illustrating embodiments of the powered device interface;

[0008] Figure 5B These are block diagrams and circuit diagrams illustrating embodiments of the power receiving device interface; and

[0009] Figure 6 This is a flowchart illustrating an embodiment of a method for implementing a powered device interface in a PoE system. Detailed Implementation

[0010] Overview

[0011] Power over Ethernet (PoE) systems include power supply equipment (PSEs) connected to powered devices (PDs) via Ethernet cabling consisting of multiple twisted-pair Ethernet cables that transmit power and data from the PSE to the PD. Such systems can be used to operate PDs that process data going to and from the network and utilize power for continuous operation. For example, a PD located away from other power sources (e.g., direct power cabling to a power outlet or outlet) can obtain power from the PSE via Ethernet cabling without relying entirely on backup batteries or other power sources.

[0012] Due to resistive losses along the Ethernet cabling length, the power supplied by the PSE may decrease as power is transmitted over the Ethernet cabling. Typically, the longer the Ethernet cabling between the PSE and the PD, the more power is lost during transmission to the PD's input side. If the PD requires more power than is available at the input side, the PSE may stop supplying power to the PD due to current protection when the PD is operating at full load. For example, a PD drawing more current than the PSE allows may be shut down by the PSE. If the PoE system includes multiple PSEs, a PSE may stop supplying power to a PD if a portion of the PD requires more power than a single PSE in the group can obtain. Such power interruptions from the PSE are detrimental to the operation of the PD, especially those without backup power.

[0013] In one embodiment, a powered device interface includes a supply sensing circuit, a demand sensing circuit, and a control circuit. The supply sensing circuit is configured to sense the amount of power allowed to be supplied by at least one power supply device via an Ethernet cable. The demand sensing circuit is configured to sense the power demand requested by the powered device. The control circuit is coupled to the supply sensing circuit and the demand sensing circuit and is configured to reduce the power demand requested by the powered device by degrading at least one of the functions of the powered device or the functions of the system in which the powered device operates when the power demand requested by the powered device exceeds the amount of power allowed to be supplied by the power supply device.

[0014] In one embodiment, a powered device in a Power over Ethernet (PoE) system includes a powered device interface and a voltage converter. The powered device interface includes: a supply sensing circuit configured to sense the amount of power that the power supply device is allowed to provide to the powered device from at least one power supply device via an Ethernet cable; a demand sensing circuit configured to sense the power demand requested by the powered device; and a control circuit coupled to the supply sensing circuit and the demand sensing circuit. The control circuit is configured to reduce the requested power demand by degrading at least one of the functions of the powered device or the functions of the system in which the powered device operates when the requested power demand exceeds the amount of power that the power supply device is allowed to provide to the powered device. The voltage converter is coupled to the powered device interface at a front end of the voltage converter. The voltage converter is configured to receive an output from the control circuit to reduce the requested power demand when the requested power demand exceeds the amount of power that the power supply device is allowed to provide to the powered device.

[0015] In one embodiment, a method for limiting the power requested by a powered device in a Power over Ethernet (PoE) system includes: sensing, via a supply sensing circuit, the amount of power that the power supply device allows to be supplied to the powered device from at least one power supply device via an Ethernet cable; sensing, via a demand sensing circuit, the power demand requested by the powered device; and reducing the power demand requested by the powered device via a control circuit coupled to the supply sensing circuit and the demand sensing circuit, the control circuit being configured to degrade at least one of the functionality of the powered device or the functionality of the system in which the powered device operates when the power demand requested by the powered device exceeds the amount of power received by the powered device.

[0016] Example Implementation

[0017] refer to Figure 1 This diagram illustrates a block representation of a powered device (PD) 100 coupled to a power supply equipment (PSE) 102 via an Ethernet cable 104. The PSE 102 supplies power and data to the PD 100 via the Ethernet cable 104. Examples of PSE 102 include, but are not limited to, network switches. Examples of PD 100 include, but are not limited to, wireless access points, Internet Protocol (IP) phones, IP cameras, retail displays, outdoor units (ODUs), and network routers. The PD 100 includes a powered device interface 106 and a voltage converter 108 for managing the operation of the PD 100 in response to power received from the PSE 102.

[0018] Powered Device Interface 106 senses the amount of power that PSE 102 allows to provide to PD 100 via Ethernet cable 104. In an embodiment, Powered Device Interface 106 includes supply sensing circuitry to sense the amount of power available to PD 100 from PSE 102 via Ethernet cable 104. The amount of power available to PSE 102 is sensed at the input side of PD 100 after transmission via Ethernet cable 104. The power sensed by Powered Device Interface 106 takes into account power losses during transmission via Ethernet cable 104 and represents the actual amount of power available to PD 100, not the amount of power leaving PSE 102. In an embodiment, Powered Device Interface 106 senses the amount of power available to PD 100 by sensing the current received by PD 100 from PSE 102 via Ethernet cable 104.

[0019] Powered Device Interface 106 senses power demands requested from PD 100 so that PSE 102 can transmit power over Ethernet cable 104. In an embodiment, Powered Device Interface 106 includes demand sensing circuitry to sense power demands requested from PD 100. Power demands can be attributed to the total number of processes or functions undertaken by PD 100, including but not limited to the processing speed of PD 100 or the number of concurrent tasks managed by PD 100. Power demands can be attributed to the operation of PD 100, the operation of one or more components of the system in which PD 100 operates (e.g., cooling components, heating components, lighting components, telecommunications components, camera or imaging components), or combinations thereof. For example, PD 100 may require 60W of power to operate at its maximum functional level; however, the power demand is not limited to a value of 60W and can be less than 60W, greater than 60W, or a value that varies over time for PD 100 depending on its real-time activity.

[0020] In an embodiment, if the actual power received from PSE 102 is insufficient to meet the power demand, the powered device interface 106 can reduce the power demand requested by PD 100. For example, if the power demand requested by PD 100 exceeds the amount of power available to PD 100 (e.g., sensed at the input side of PD 100), the powered device interface 106 reduces the power demand requested by PD 100. The power demand requested by PD 100 can be reduced so that the power demand falls within the amount of power available to PD 100, thus preventing PSE 102 from cutting off the power supply to PD 100. In an embodiment, the powered device interface 106 includes control circuitry coupled to supply sensing circuitry and demand sensing circuitry to reduce the power demand requested by PD 100 when it exceeds the amount of power available to PD 100 from PSE 102 via Ethernet cable 104. In an embodiment, when the power demand requested by PD 100 exceeds the power available to PD 100, the control circuit transmits an output to the front end of voltage converter 108 to reduce the power demand requested by PD 100. Example voltage converter 108 includes, but is not limited to, a DC-DC converter.

[0021] In one embodiment, when the power demand requested by PD 100 exceeds the amount of power available to PD 100, the powered device interface 106 reduces the power demand requested by PD 100 by limiting the current utilized by PD 100. In another embodiment, when the power demand requested by PD 100 exceeds the amount of power available to PD 100, the powered device interface 106 reduces the power demand requested by PD 100 by degrading the functionality of PD 100 or the functionality of the system in which PD 100 operates. Examples of functional degradation include, but are not limited to: reducing the processing speed of PD 100, reducing the number of concurrent tasks managed by PD 100, or shutting down or reducing the power draw of system components (e.g., heating components, cooling components, lighting components, telecommunications components, camera or imaging resolution, camera or imaging speed).

[0022] PSE 102 may include one or more power controllers, wherein, Figure 2 An example of an embodiment with a single power controller is provided, and in which, Figure 3 Examples of embodiments with multiple power controllers are provided.

[0023] refer to Figure 2This diagram illustrates an example of a PoE system including a Powered Device Interface 106 of a PD 100. A PSE 102 includes a single PSE controller 200 configured to transmit power and data to the PD 100 via an Ethernet cable 104. The Ethernet cable 104 is coupled between the PSE 102 and a connector 202 of the PD 100. Examples of connector 202 include, but are not limited to, an RJ45 connector. The PSE controller 200 outputs data and power to the connector 202 of the PSE 102 via connection 204, where a twisted pair 206 transmits data and power to the connector 202 of the PD 100. The PD 100 includes a connection 208 coupled to connector 202 to receive power and data transmitted via the twisted pair 206 of the Ethernet cable 104. Connections 204 and 208 may include, but are not limited to, transducers and electrical wiring. PD 100 includes a diode or active bridge 210 coupled between connection 208 and power received interface 106. In an embodiment, power received interface 106 senses the power available at the input side of PD 100 by sensing the power received from the diode or active bridge 210. In an embodiment, power received interface 106 compares the amount of power received from the diode or active bridge 210 with the power demand of PD 100 to determine whether the power demand exceeds the actual power allowed by PSE 100. When the power demand requested by PD 100 exceeds the power available to PD 100, power received interface 106 reduces the power demand requested by PD 100. In an embodiment, when the power demand requested by PD 100 exceeds the power available to PD 100, power received interface 106 transmits an output via one or more connections 212 to the front end of voltage converter 108 to reduce the power demand requested by PD 100.

[0024] refer to Figure 3A block diagram representation of an example PoE system with multiple PSE controllers is shown. PSE 102 is shown as including a first PSE controller 300A and a second PSE controller 300B. The first PSE controller 300A outputs data and power to connector 302 of PSE 102 via connection 304, where twisted pair cable 306A transmits data and power to connector 302 of PD 100. Examples of connector 302 include, but are not limited to, an RJ45 connector. The second PSE controller 300B outputs data and power to connector 302 of PSE 102 via connection 304, where twisted pair cable 306B transmits data and power to connector 302 of PD 100. PD 100 includes a connection 308 coupled to connector 302 to receive power and data transmitted via twisted pair cables 306A and 306B through Ethernet cable 104. Connections 304 and 308 may include, but are not limited to, transducers and electrical wiring. PD 100 includes a diode or active bridge 310 coupled between connection 308 and power receiving interface 106. In an embodiment, power receiving interface 106 includes: a first power receiving interface 106A configured to receive power transmitted from a first PSE controller 300A; and a second power receiving interface 106B configured to receive power transmitted from a second PSE controller 300B.

[0025] In an embodiment, powered device interfaces 106A and 106B sense the power received at the input side of PD 100 by sensing the power received from diodes or active bridge 310. In an embodiment, powered device interface 106A compares the amount of power received from diodes or active bridge 310 (i.e., from the first PSE controller 300A) with the power demand of PD 100 to determine whether the power demand exceeds the actual amount of power received from the first PSE controller 300A. When the power demand requested by PD 100 exceeds the amount of power available to PD 100, powered device interface 106A reduces the power demand requested by PD 100. In an embodiment, when the power demand requested by PD 100 exceeds the amount of power allowed by the first PSE controller 300A, powered device interface 106A transmits an output via one or more connections 312 to the front end of voltage converter 108A to reduce the power demand requested by PD 100.

[0026] In one embodiment, the powered device interface 106B compares the power received from the diode or active bridge 310 (i.e., from the second PSE controller 300B) with the power demand of PD 100 to determine whether the power demand exceeds the actual power received from the second PSE controller 300B. When the power demand requested by PD 100 exceeds the power available to PD 100, the powered device interface 106B reduces the power demand requested by PD 100. In another embodiment, when the power demand requested by PD 100 exceeds the power allowed by the second PSE controller 300B, the powered device interface 106B transmits an output via one or more connections 312 to the front end of the voltage converter 108B to reduce the power demand requested by PD 100.

[0027] Powered device interfaces 106A and 106B can control the power demand of PD 100 to prevent the power supply from PSE 102 to PD 100 from being shut down if the power from one or both of PSE controllers 300A or 300B is insufficient to supply the current demand from PD 100. For example, powered device interfaces 106A or 106B can reduce the demand of PD 100 when they sense that the power allowed by one or both of PSE controllers 300A or 300B is insufficient. As an example scenario, each of PSE controllers 300A and 300B can supply 30W to PD 100, for a total of approximately 60W (assuming no loss during transmission over Ethernet cable 104). If the powered device interface 106A senses a power demand of 35W and the powered device interface 106B senses a power demand of 25W, then the powered device interface 106A can limit the 35W power demand to 30W to prevent the PSE 102 from stopping the current supply to the PD 100 because the 35W power demand exceeds the 30W supply from the PSE controller 300A. Simultaneously, the powered device interface 106A or 106B can (e.g., via...) Figure 5A The alarm circuit shown issues an alarm signal to prompt the system to react accordingly, namely, to shut down or reduce the power draw of system components to reduce power consumption to a total of 30W plus 25W. Although the example scenario is described using the listed power supply and power demand values, the values ​​of PD 100 and PSE 102 are not limited to those listed and may include values ​​that are greater or less than those listed.

[0028] refer to Figure 4The diagram shows a graph of the output voltage versus output current of the power received by PD 100 from PSE 102. Since the power demand from PD 100 is less than the maximum permissible power of PSE 102 (shown as "Pmax"), the powered device interface 106 can implement constant voltage control on PD 100. If the current increases (e.g., by increasing the demand of PD 100), the powered device interface 106 can implement voltage control to limit the voltage output from PSE 102. For example, when the current increases to exceed the current level associated with the maximum power at a given output voltage (e.g., the current increases to exceed "Iknee"), the powered device interface 106 can implement constant power control to limit the output voltage and keep PD 100 below the maximum permissible current of PSE 102 (shown as "Imax").

[0029] refer to Figure 5A A block diagram and circuit diagram of an embodiment of a powered device interface 106 are shown. The powered device interface 106 includes supply sensing circuitry (generally indicated by 500) configured to sense the amount of power received by a powered device (generally indicated by 502). For example, the amount of power sensed by the supply sensing circuitry 500 may include the power received by the powered device interface 106 at the front end of the PD 100. The powered device interface 106 is shown to include control circuitry (generally indicated by 504) configured to reduce the power demand requested by the PD 100 when the power demand requested by the PD 100 exceeds the amount of power received by the PD 100. Figure 5A In the embodiment shown, the control circuit 504 utilizes a reference voltage ("VREF") that depends on the power value ("PLIMIT").

[0030] In this embodiment, the power value (“PLIMIT”) is provided at the physical level from the classification phase of PSE 102 and PD 100 (e.g., mutual identification via hardware connection between PSE 102 and PD 100). This classification can set an initial power budget for PD 100. For example, PD 100 may include one or more pins for creating a classification current output (e.g., from a resistor) to transmit a current classification indicating a basic or initial power requirement or budget to PSE 102. PSE 102 can then confirm whether the power allowed by PSE 102 satisfies PD 100's power budget request, or whether PD 100 should reduce the amount of power requested by PD 100 due to PSE 102's capability limitations. After classification, the basic or initial power level requested by PD 100 is determined.

[0031] In this embodiment, the power value (“PLIMIT”) is provided or modified via demand sensing circuitry of the powered device interface 106. For example, refer to... Figure 5B A block diagram representation and circuit diagram of an embodiment of a powered device interface 106 having a demand sensing circuit generally indicated as 506 are shown. In this embodiment, the demand sensing circuit 506 receives the power demand of PD 100 as input (generally shown as 508) and outputs a power value (“PLIMIT”) as output, wherein control circuitry 504 can access the power value (“PLIMIT”) to determine whether the power demand of PD 100 exceeds the power available to PD 100. In this embodiment, the demand sensing circuit 506 receives the power demand from the microcontroller of PD 100. (Refer again) Figure 5A The control circuit 504 includes an output 510 to the voltage converter 108. In an embodiment, when the power demand requested by the PD 100 exceeds the amount of power available to the PD 100, the output 510 is passed to the front end of the voltage converter 108 to reduce the power demand requested by the PD 100. The power demand can be reduced by degrading the functionality of the PD 100 or the system in which the PD 100 operates (e.g., reducing the usage time of cooling components (e.g., fan uptime), reducing the usage time of heating components (e.g., heater uptime), reducing camera or imaging resolution, reducing camera or imaging speed, reducing the processing speed of the PD 100, reducing the number of concurrent tasks managed by the PD 100), or a combination thereof. In an embodiment, the power budget of the PD 100 can be increased to a higher value than determined in the previous classification. For example, the power demand may increase due to lower cable power loss along the Ethernet cable compared to the cable loss state during the previous classification. The cable length of the Ethernet cabling in a PoE system can affect the actual amount of power available to a given powered device, for example, due to resistive losses in the cable. If the cable loss is low due to the short cable length, the remaining power in the power budget can be allocated to PD 100.

[0032] refer to Figure 6 The diagram illustrates a flowchart of a method 600 for implementing a powered device interface 106 in a PoE system. At 602, the amount of power received by the powered device from the power supply device via an Ethernet cable is sensed. For example, the powered device interface 106 senses the amount of power received from the PSE 102 via an Ethernet cable 104. In this embodiment, a supply sensing circuit 500 of the powered device interface 106 senses the amount of power received from the PSE 102 via the Ethernet cable 104.

[0033] At 604, the power demand requested by the powered device is sensed. For example, the powered device interface 106 senses the power demand requested by PD 100. In an embodiment, the demand sensing circuit 506 of the powered device interface 106 senses the power demand requested by PD 100 and outputs a value accessible to the powered device interface 106 to compare it with the amount of power received from PSE 102.

[0034] At point 606, when the power demand requested by the powered device exceeds the power available to the powered device, the power demand requested by the powered device is reduced. For example, the powered device interface 106 can reduce the power demand requested by PD 100 when PD 100's power demand exceeds the power available to PD 100. In an embodiment, the control circuit 504 of the powered device interface 106 generates an output to the voltage converter 108 to reduce the power demand requested by PD 100 when PD 100's power demand exceeds the power available to PD 100.

[0035] Although a series of steps have been described in conjunction with Method 600, fewer of the described steps and / or additional steps can be performed. Furthermore, although the steps have been described in a specific order, the steps in Method 600 can be performed in a different order.

[0036] As will be apparent to those skilled in the art, any range or device value given herein may be extended or modified without losing the desired effect.

[0037] Although the subject matter has been described in language specific to structural features and / or methodological actions, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or actions described above. Rather, the specific features and actions described above are disclosed as examples of implementing the claims.

[0038] It will be understood that the above benefits and advantages may relate to one embodiment or several embodiments. The embodiments are not limited to embodiments that solve any or all of the stated problems, or embodiments that have any or all of the stated benefits and advantages. It will also be understood that a reference to "one" means one or more of those items.

[0039] Unless otherwise stated, the order in which the operations in the examples of the disclosures shown and described herein are not required. That is, unless otherwise stated, these operations may be performed in any order, and the examples of this disclosure may include more or fewer operations than those disclosed herein. For example, it is conceivable that performing or executing a particular operation before, simultaneously with, or after another operation is also within the scope of various aspects of this disclosure.

[0040] When describing elements or examples thereof in various aspects of this disclosure, the articles “a,” “an,” “the,” and “said” are intended to indicate the presence of one or more of these elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements besides those listed. The term “exemplary” is intended to mean “example.” The phrase “one or more of the following: A, B, and C” means “at least one of A and / or at least one of B and / or at least one of C.”

[0041] Having described in detail various aspects of this disclosure, it will be apparent that modifications and variations may be made without departing from the scope of these aspects as defined by the appended claims. Because various changes can be made to the above-described structures, products, and methods without departing from the scope of these disclosures, it is intended that all subject matter contained in the foregoing specification and illustrated in the accompanying drawings be construed as illustrative rather than restrictive.

Claims

1. A power receiving interface for a power receiving device in a system employing Power over Ethernet, the power receiving interface comprising: A supply sensing circuit configured to sense the amount of power allowed to be supplied via an Ethernet cable by at least one power supply device; Demand sensing circuit, configured to sense the power demand requested by the powered device; as well as A control circuit coupled to the supply sensing circuit and the demand sensing circuit is configured to reduce the power demand requested by the powered device by degrading at least one of the functions of the powered device or the functions of the system in which the powered device operates when the power demand requested by the powered device exceeds the amount of power that the power supply device is allowed to provide to the powered device. The control circuit is also configured to transmit an output to the front end of a voltage converter to reduce the power demand requested by the powered device when the power demand requested by the powered device exceeds the amount of power that the power supply device is allowed to provide to the powered device.

2. The power receiving device interface as described in claim 1, wherein, This voltage converter includes a DC-DC converter.

3. The power receiving device interface as described in claim 1, wherein, The power supply sensing circuit is configured to sense the amount of power that the power supply device is allowed to provide to the powered device by sensing the current that the power supply device is allowed to provide to the powered device through the Ethernet cable and the input voltage of the powered device.

4. The power receiving device interface as described in claim 1, wherein, The control circuit is configured to reduce the power demand requested by the powered device by limiting the current used by the powered device when the power demand requested by the powered device exceeds the amount of power that the power supply device is allowed to provide to the powered device.

5. The power receiving device interface as described in claim 1, wherein, The control circuit is configured to reduce the power demand requested by the powered device by degrading the functionality of the powered device when the power demand requested by the powered device exceeds the amount of power that the power supply device is allowed to provide to the powered device, wherein the functionality of the powered device includes the number of concurrent tasks managed by the powered device.

6. The power receiving device interface as described in claim 1, wherein, This power supply device allows power to be supplied to the powered device from at least one power supply device via an Ethernet cable, which comes from a single power controller of that power supply device.

7. The power receiving device interface as described in claim 1, wherein, This power supply device allows power supplied to the powered device from at least one power supply device via an Ethernet cable from multiple power controllers.

8. A powered device in a system employing Power over Ethernet, the powered device comprising: Power receiving interface, the power receiving interface including: A supply sensing circuit is configured to sense the amount of power that the power supply device allows to provide to the powered device from at least one power supply device via an Ethernet cable. A demand sensing circuit configured to sense the power demand requested by the powered device; and A control circuit coupled to the supply sensing circuit and the demand sensing circuit, the control circuit being configured to reduce the power demand requested by the powered device by degrading at least one of the functions of the powered device or the functions of the system in which the powered device operates when the power demand requested by the powered device exceeds the amount of power that the power supply device is allowed to provide to the powered device; and An alarm circuit configured to send a warning signal to the system to reduce the system's power consumption; and A voltage converter, the voltage converter being coupled to the interface of the powered device at the front end of the voltage converter, the voltage converter being configured to receive an output from the control circuit to reduce the power demand requested by the powered device when the power demand requested by the powered device exceeds the amount of power that the power supply device is allowed to provide to the powered device.

9. The power receiving device as claimed in claim 8, wherein, This voltage converter includes a DC-DC converter.

10. The power receiving device as claimed in claim 8, wherein, The supply sensing circuit is configured to sense the amount of power that the power supply device is allowed to provide to the powered device by sensing the current received by the powered device through the Ethernet cable and the input voltage of the powered device.

11. The power receiving device as claimed in claim 8, wherein, The control circuit is configured to reduce the power demand requested by the powered device by limiting the current used by the powered device when the power demand requested by the powered device exceeds the amount of power that the power supply device is allowed to provide to the powered device.

12. The power receiving device interface as claimed in claim 8, wherein, The control circuit is configured to reduce the power demand requested by the powered device by degrading the functionality of the powered device when the power demand requested by the powered device exceeds the amount of power that the power supply device is allowed to provide to the powered device, wherein the functionality of the powered device includes the number of concurrent tasks managed by the powered device.

13. The power receiving device interface as described in claim 8, wherein, This power supply device allows power to be supplied to the powered device from at least one power supply device via an Ethernet cable, which comes from a single power controller of that power supply device.

14. The power receiving device interface as claimed in claim 8, wherein, This power supply device allows power supplied to the powered device from at least one power supply device via an Ethernet cable from multiple power controllers.

15. A method for limiting the power requested by a powered device in a Power over Ethernet (PoE) system, the method comprising: The power supply sensing circuitry is used to sense the amount of power that the power supply device is allowed to provide to the powered device from at least one power supply device via an Ethernet cable. The power demand requested by the powered device is sensed through a demand sensing circuit; and The power demand requested by the powered device is reduced by a control circuit coupled to the supply sensing circuit and the demand sensing circuit. The control circuit is configured to degrade at least one of the functions of the powered device or the functions of the system in which the powered device operates when the power demand requested by the powered device exceeds the amount of power that the power supply device is allowed to provide to the powered device. The reduction of the power demand requested by the powered device includes: when the power demand requested by the powered device exceeds the amount of power that the power supply device is allowed to provide to the powered device, transmitting an output to the front end of the voltage converter to reduce the power demand requested by the powered device.

16. The method of claim 15, wherein, Sensing the amount of power received by the powered device from at least one power supply device via an Ethernet cable through a supply sensing circuit includes: sensing the current received by the powered device from at least one power supply device via the Ethernet cable through the supply sensing circuit.

17. The method of claim 15, wherein, This power supply device allows power to be supplied to the powered device from at least one power supply device via an Ethernet cable, which comes from a single power controller of that power supply device.

18. The method of claim 15, wherein, This power supply device allows power supplied to the powered device from at least one power supply device via an Ethernet cable from multiple power controllers.

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