Negotiable PoE voltage for improved efficiency based on cable and powered device losses

• US 9,847,884 B2
• Filed: 11/04/2014
• Issued: 12/19/2017
• Est. Priority Date: 11/04/2014
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Balasubramanian, Koussalya
• Primary Examiner(s): JOHNSON, TERRELL S
• Application Number:
  US14/532,148
• Publication Number:
  US 20160127135A1
• Time in Patent Office: 1,141 Days
• CPC Class Codes: G01R 27/08 Measuring resistance by measuring both voltage and current
• CPC Class Codes: G01R 31/086 in power transmission or distribution networks, i.e. with interconnected conductors
• CPC Class Codes: G06F 1/266 Arrangements to supply power to external peripherals either directly from the computer or under computer control, e.g. supply of power through the communication port, computer controlled power-strips
• CPC Class Codes: H04L 12/10 Current supply arrangements
• CPC Class Codes: H04L 12/40045 Details regarding the feeding of energy to the node from the bus
• CPC Class Codes: H04L 43/50 Testing arrangements

Abstract

A powered device (PD) receives a Power-over-Ethernet (PoE) voltage to power the PD over a cable from Power Source Equipment (PSE) configured to output a requested one of multiple candidate PoE voltages to the cable. The PD determines a preferred PoE voltage among the multiple candidate PoE voltages that minimizes a total power loss due to (i) the cable, and (ii) a power loss of the PD that would result if the PD were powered through the cable. The PD requests the preferred PoE voltage from the PSE, receives the preferred PoE voltage from the PSE, and operates at the preferred PoE voltage.

Claims

1. A method comprising:

at a powered device (PD) configured to receive a Power-over-Ethernet (PoE) voltage to power the PD over a cable from a Power Source Equipment (PSE) that is configured to output a requested one of multiple candidate PoE voltages to the cable;

determining for each candidate PoE voltages, respectively;

a power loss in the cable that would result from the candidate PoE voltage;

a power loss in the PD that would result if the PD were powered through the cable with the candidate PoE voltage, the power loss in the PD equal to a product of a predetermined power rating of the PD and a voltage conversion efficiency loss associated with converting a voltage received by the PD to an operating voltage used to operate circuits in the PD; and

a total power loss as a sum of the power losses of the cable and the PD;

selecting as a preferred PoE voltage the candidate PoE voltage that minimizes the total power loss;

requesting the preferred PoE voltage from the PSE;

receiving the preferred PoE voltage from the PSE; and

operating at the preferred PoE voltage.

2. The method of claim 1, wherein the respective cable power loss is determined based on the predetermined power rating of the PD, the PoE voltage, and an electrical resistance of the cable.

3. The method of claim 2, wherein the determining the PD power loss includes determining the PD power loss based on the predetermined power rating of the PD and a Direct Current-to-Direct Current (DC-DC) efficiency loss associated with converting the PoE voltage to the operating voltage used to operate the circuits in the PD.

4. The method of claim 2, further comprising:

determining a cable length;

determining a cable type that indicates an electrical resistance per unit length; and

determining the electrical resistance of the cable based on the cable length and the cable type.

5. The method of claim 4, further comprising, at the PD:

receiving from the PSE one or more data messages that specifies the multiple candidate PoE voltages as voltages that the PSE is able to provide to the PD;

after the determining, sending a data message to the PSE requesting the preferred PoE voltage; and

receiving from the PSE an acknowledgment of the request.

6. The method of claim 5, further comprising, at the PSE:

sending to the PD the one or more data messages that specifies the multiple candidate PoE voltages as voltages that the PSE is able to provide to the PD;

receiving from the PD the data message requesting the preferred PoE voltage; and

responsive to the data message requesting the preferred PoE voltage;

sending the acknowledgement; and

outputting the preferred PoE voltage to the PD.

7. The method of claim 4, wherein the cable length and cable type is contained in the data message received from the PSE.

8. The method of claim 4, wherein the determining a cable length includes determining the cable length using a time domain reflectometry technique performed at the PD.

9. The method of claim 4, further comprising:

sending a probe voltage to the PD;

at the PD, responsive to the probe voltage, sinking a current from the PSE indicative of the preferred PoE voltage; and

at the PSE, sensing the sinking current and responsive thereto, presenting the preferred PoE voltage to the PD.

10. The method of claim 1, further comprising, at the PSE:

generating the multiple candidate PoE voltages; and

responsive to the requesting from the PD, selecting and outputting to the PD the preferred one of the multiple candidate PoE voltages.

11. The method of claim 1, further comprising performing the determining, for each of the candidate voltages, the power loss in the cable, the power loss in the PD, and the total power loss, without applying any of the candidate PoE voltages to the PD.

18. The method of claim 11, further comprising performing the selecting without applying any of the candidate PoE voltages to the PD.

12. An apparatus comprising:

a powered device (PD) configured to receive a Power-over-Ethernet (PoE) voltage to power the PD over a cable from a Power Source Equipment (PSE) that is configured to output a requested one of multiple candidate PoE voltages to the cable, wherein the PD includes a controller to;

determine for each candidate PoE voltage, respectively;

a power loss in the cable that would result from the candidate PoE voltage;

a power loss in the PD that would result if the PD were powered through the cable with the candidate PoE voltage, the power loss in the PD equal to a product of a predetermined power rating of the PD and a voltage conversion efficiency loss associated with converting a voltage received by the PD to an operating voltage used to operate circuits in the PD; and

a total power loss as a sum of the power losses of the cable and the PD;

select as a preferred PoE voltage the candidate PoE voltage that minimizes the total power loss;

request the preferred PoE voltage from the PSE;

receive the preferred PoE voltage from the PSE; and

operate at the preferred PoE voltage.

13. The apparatus of claim 12, wherein the controller determines a respective cable power loss by determining the cable power loss based on the predetermined power rating of the PD, the PoE voltage, and an electrical resistance of the cable.

14. The apparatus of claim 13, wherein the PD includes a Direct Current-to-Direct Current (DC-DC) converter to convert the received PoE voltage to the operating voltage used to operate the PD.

15. The apparatus of claim 13, wherein the controller further:

determines a cable length;

determines a cable type that indicates a electrical resistance per unit length; and

determines the electrical resistance of the cable based on the cable length and the cable type.

16. The apparatus of claim 15, wherein the controller further:

receives from the PSE a data message that indicates the multiple candidate PoE voltages as voltages that the PSE is able to provide to the PD;

after the preferred PoE voltage is determined, sends a data message to the PSE requesting the preferred PoE voltage; and

receives from the PSE an acknowledgment of the request.

17. The apparatus of claim 16, wherein the controller determines the cable length and the cable type from information contained in the data message received from the PSE.

19. A system comprising:

a powered device (PD) configured to receive a Power-over-Ethernet (PoE) voltage to power the PD over a cable, the PD including a PD controller; and

Power Source Equipment (PSE), including;

a voltage generator to generate multiple candidate PoE voltages and output a selected one of the PoE voltages to the cable to power the PD; and

a PSE controller coupled to the voltage generator, wherein;

the PSE is configured to advertise the multiple candidate PoE voltages to the PD;

the PD is configured to;

determine for each candidate PoE voltage, respectively;

a power loss in the cable that would result from the candidate PoE voltage;

a power loss in the PD that would result if the PD were powered through the cable with the candidate PoE voltage, the power loss in the PD equal to a product of a predetermined power rating of the PD and a voltage conversion efficiency loss associated with converting a voltage received by the PD to an operating voltage used to operate circuits in the PD; and

a total power loss as a sum of the power losses of the cable and the PD;

select as a preferred PoE voltage the candidate PoE voltage that minimizes the total power loss; and

the PD and the PSE are configured to negotiate with each other to cause the PSE to provide the preferred PoE voltage to the cable to power the PD.

20. The system of claim 19, wherein:

the PD further requests the preferred PoE voltage from the PSE; and

responsive to the request from the PD, the PSE selects and outputs the preferred PoE to power the PD.

21. The system of claim 20, wherein:

the PSE advertises by sending a data message to the PD that lists the multiple candidate PoE voltages as voltages that the PSE is able to provide to the PD; and

responsive to the request from the PD, the PSE further sends an acknowledgement to the PD.

22. The system of claim 20, wherein the PD further determines the respective cable power loss based on the predetermined power rating of the PD, the PoE voltage, and an electrical resistance of the cable.

23. The system of claim 22, wherein the PD further determines the PD power loss based on the predetermined power rating of the PD and a Direct Current-to-Direct Current (DC-DC) efficiency loss associated with converting the PoE voltage to the operating voltage used to operate the circuits in the PD.

24. The system of claim 19, wherein the PSE determines the preferred PoE voltage based on a total power loss due to the cable, the PD power loss that would result if the PD were powered by the PSE through the cable, and a PSE power loss.