Method and apparatus for detecting and fixing faults in an inline-power capable ethernet system

• US 8,184,525 B2
• Filed: 06/07/2005
• Issued: 05/22/2012
• Est. Priority Date: 05/25/2005
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Karam, Roger
• Primary Examiner(s): Phillips, Hassan
• Assistant Examiner(s): Tsegaye, Saba
• Application Number:
  US11/147,543
• Publication Number:
  US 20070011547A1
• Time in Patent Office: 2,541 Days
• Field of Search: 370216-218, 370/244, 370/410, 370/908, 361/42, 361/908, 379/413, 714/11
• US Class Current: 370/216
• 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 25/08 Modifications for reducing interference; Modifications for reducing effects due to line faults ; Receiver end arrangements for detecting or overcoming line faults
• CPC Class Codes: H04L 49/35 Switches specially adapted for specific applications
• CPC Class Codes: H04L 69/40 for recovering from a failure of a protocol instance or entity, e.g. service redundancy protocols, protocol state redundancy or protocol service redirection management of faults, events, alarms or notifications in data switching networks H04L41/06
• CPC Class Codes: Y10S 370/908 Local area network

Abstract

Methods and apparatus are disclosed for detecting ground faults in an Ethernet system. An Ethernet switch is configured to provide inline power to a plurality of ports each having positive and negative rails. Current is injected into selected rails of a port and ground isolation is temporarily broken for the port. A detected mismatch in current levels between the positive and negative rails of the port indicates a ground fault in the port.

Claims

1. A system, comprising:

a floating power source isolated from ground, where the floating power source provides inline power to a plurality of Ethernet ports and is disposed between a positive rail and a negative rail;

a current sensing circuit disposed on each of the positive and negative rails of the plurality of Ethernet ports, respectively; and

a find-port circuit coupled to at least one of the positive and negative rails, where the find-port circuit;

selectively couples a grounded power source to the at least one of the positive and negative rails to break ground isolation for one or more of the plurality of Ethernet ports; and

detects a current mismatch between the positive and negative rails of one or more of the plurality of Ethernet ports by comparing currents sensed by each of the respective current sensing circuits, wherein a current on the positive rail and a current on the negative rail are both non-zero.

2. The system of claim 1, where periodically breaking ground isolation includes detecting a ground fault on one or more of the plurality of Ethernet ports.

3. The system of claim 2, where the find-port circuit is operated under software command.

4. The system of claim 1, where the system is to cause a periodic isolation cancellation to search for a ground fault on one or more of the plurality of Ethernet ports where during a period of isolation a fault on more than one port causes the find-port circuit to flag the one or more of the plurality of Ethernet ports involved.

5. The system of claim 1, where the system is to cancel isolation of one or more of the positive and negative rails of a selected Ethernet port when a powered device (PD) connected to the selected Ethernet port has been successfully discovered according to the IEEE 802.3af standard, but has yet to be powered by said selected port.

6. The system of claim 1, comprising:

a floating resistance coupled to the floating power source and the negative rails for providing isolation from ground for the plurality of Ethernet ports, the floating resistance including a voltage divider sensing node;

a ground fault circuit operatively coupled to the voltage divider sensing node, where the ground fault circuit senses the current flowing through the floating resistance; and

where the ground fault circuit detects a ground fault in one of the plurality of Ethernet ports when the current detected at the voltage divider sensing node exceeds a predefined level.

7. The system of claim 6, where one or more of the plurality of Ethernet ports detected as having ground faults are powered down.

8. The system of claim 1, where one or more of the plurality of Ethernet ports have ground isolation broken simultaneously.

9. The system of claim 1, where one of the plurality of Ethernet ports selectively has ground isolation broken.

10. The system of claim 1, where one of the plurality of Ethernet ports undergoing a discovery process according to IEEE 802.3af is scanned for ground faults prior to powering up an Ethernet Powered Device (PD).

11. The system of claim 10, where the one of the plurality of Ethernet ports is not powered up if a ground fault is detected.

12. An Ethernet system for detecting ground faults, comprising:

an Ethernet switch configured to provide inline power to a plurality of Ethernet ports, each of said plurality of Ethernet ports including a positive rail and a negative rail;

a floating power source isolated from ground and operatively disposed in said Ethernet switch between said positive and negative rails;

current sensing circuitry disposed on each of the positive and negative rails of said plurality of Ethernet ports, respectively;

find-port circuitry coupled to at least one of said rails, the find-port circuitry being configured to;

selectively couple a grounded power source to at least one of said rails, breaking ground isolation for the plurality of said Ethernet ports; and

detect a current mismatch between the positive rail and the negative rail of one or more of the plurality of Ethernet ports by comparing currents sensed by each of the respective current sensing circuitries, wherein a current present on the positive rail and a current present on the negative rail are both non-zero;

a floating resistance coupled to the power source and the negative rails, the floating resistance providing isolation from ground for the plurality of the Ethernet ports, the floating resistance including a voltage divider sensing node; and

ground fault circuitry operatively coupled to the voltage divider sensing node, the ground fault circuitry configured to sense a sensed current flowing through the floating resistance and configured to detect a ground fault in one of the plurality of Ethernet ports of the Ethernet switch when the sensed current detected at the voltage divider sensing node exceeds a predefined level.

13. The Ethernet system of claim 12, where an Ethernet port undergoing a discovery process according to IEEE 802.3af is scanned for ground faults prior to powering up an Ethernet Powered Device (PD).

14. The Ethernet system of claim 13, where the Ethernet port is not powered up if a ground fault is detected.

15. An apparatus, comprising:

an Ethernet switching means to provide inline power to a plurality of Ethernet ports, where an Ethernet port includes a positive rail and a negative rail;

a first power source means operatively disposed in the Ethernet switching means between the positive and negative rails of the plurality of Ethernet ports;

a current sensing circuit means disposed on each of the positive and negative rails of the plurality of Ethernet ports, respectively;

a find-port circuit means coupled to at least one of the positive and negative rails of the plurality of Ethernet ports;

where the find-port circuit means selectively couples a second power source means to the at least one of the positive and negative rails to break ground isolation for the plurality of Ethernet ports; and

a means for detecting a current mismatch between the positive and negative rails of one or more of the plurality of Ethernet ports by comparing currents sensed by each of the respective current sensing circuit means, wherein a current on the positive rail and a current on the negative rail are both non-zero;

where a floating resistance means is coupled to the first power source means and the negative rails of the plurality of Ethernet ports to provide isolation from ground for the plurality of Ethernet ports,

where the floating resistance means includes a voltage divider sensing node;

a ground fault circuit means operatively coupled to the voltage divider sensing node to sense the current flowing through the floating resistance means and to detect a ground fault in one of the plurality of Ethernet ports of the Ethernet switching means when the current detected at the voltage divider sensing node by the ground fault circuit exceeds a predefined level.

16. The apparatus of claim 15, where one or more of the Ethernet ports of the Ethernet switching means comprise means for breaking ground isolation simultaneously.

17. The apparatus of claim 15, where a selected one of the plurality of Ethernet ports has ground isolation broken.

18. The apparatus of claim 15, comprising means for scanning for ground faults prior to powering up an Ethernet Powered Device (PD).

19. The apparatus of claim 18, comprising means for not powering up a scanned port if a ground fault is detected.

20. A method for detecting ground faults in an Ethernet system comprising:

providing Ethernet switching means for providing inline power to a plurality of Ethernet ports, wherein each of the plurality of Ethernet ports include a positive rail and a negative rail;

providing a floating power source isolated from ground that is disposed between the positive and negative rails;

providing a current sensing circuit disposed on each of the positive and negative rails of the plurality of Ethernet ports, respectively;

providing a find-port circuit coupled to at least one of the positive and negative rails that selectively couples a grounded power source to the at least one of the positive and negative rails to break ground isolation for at least one of the plurality of Ethernet ports; and

detecting a current mismatch between the positive and negative rails of one or more of the plurality of Ethernet ports by comparing currents sensed by each of the respective current sensing circuits, wherein a current on the positive rail and a current on the negative rail are both non-zero.

21. The method of claim 20, further comprising breaking ground isolation for two or more of the plurality of Ethernet ports.

22. The method of claim 20, further comprising periodically breaking ground isolation for at least one of the plurality of Ethernet ports in the process of detecting ground faults.

23. The method of claim 20, wherein said method may be operated under software control.

24. The method of claim 20, further comprising:

locating a faulty one of the plurality of Ethernet ports responsive to the detection of the current mismatch; and

flagging the located Ethernet port as faulty.

25. The method of claim 20, wherein a fault is indicated if a current increase is detected on one of the positive and negative rails of one of the plurality of the Ethernet ports that is substantially equal in magnitude to the current delivered in or out of by the floating power source.

26. The method of claim 25 wherein said method is used in conjunction with the discovery process of the IEEE 802.3af standard.

27. The method of claim 26, wherein a selected port is scanned for ground faults prior to powering a Powered Device.

28. The method of claim 27, wherein, if a ground fault is detected, the discovery process is halted prior to the port being powered up.

29. The method of claim 20, further comprising:

connecting the corresponding rails of one of the plurality of Ethernet ports one rail at a time after a successful discovery according to the IEEE 802.3af standard but before power is applied;

switching in the grounded power source; and

scanning for ground faults.

30. The method of claim 29, wherein the scanned port is not powered up if a ground fault is detected.