Distinguishing network interface card from short circuit condition in power over ethernet system

• US 7,230,412 B2
• Filed: 10/19/2005
• Issued: 06/12/2007
• Est. Priority Date: 01/25/2005
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Linear Technology Corporation (Analog Devices, Inc.)
• Inventors: Stineman, John Arthur Jr., Heath, Jeffrey Lynn
• Primary Examiner(s): Hirshfeld; Andrew H.
• Assistant Examiner(s): NGUYEN, HOAI AN D
• Application Number:
  US11/252,585
• Publication Number:
  US 20060164062A1
• Time in Patent Office: 601 Days
• Field of Search: 324/76.11, 324/602, 324/605, 324/600, 324/606, 324/647, 324/656, 324/665, 324/672, 324/679, 324/705, 370/241, 709/220, 709/224
• US Class Current: 324/76.11
• CPC Class Codes: H04L 12/10 Current supply arrangements
• CPC Class Codes: H04L 49/351 for local area network [LAN], e.g. Ethernet switches

Abstract

Novel system and methodology for distinguishing a Network Interface Card (NIC) from a short circuit condition in a Power over Ethernet (PoE) system. A system for providing power to a powered device (PD) includes a PD probing circuit that generates a detection signal supplied to a device being probed and determines a response signal produced in response to the detection signal, and a control circuit that determines a detection value based on the response signal. The control circuit detects a short circuit if the detection value is in a first predetermined range, and detects a NIC if the detection value is in a second predetermined range outside of the first predetermined range.

Claims

1. A system for providing power to a powered device (PD) in a Power over Ethernet (PoE) system, comprising:

a PD probing circuit for determining first and second response signals produced in response to respective first and second detection signals supplied over an Ethernet link to a device being probed, and

a control circuit, configured for;

controlling the PD probing circuit to supply over the Ethernet link the second detection signal greater than the first detection signal if the first response signal does not exceed a threshold value, and

determining that a short circuit condition is detected if a detection value defined by a difference between the second response signal and the first response signal is in a first predetermined range, and determining that a Network Interface Card connected to the Ethernet link is detected if the detection value is in a second predetermined range outside of the first predetermined range.

2. The system of claim 1, wherein the control circuit is configured for determining that an improper device is detected if the detection value is in a third predetermined range outside of the first and second predetermined ranges.

3. The system of claim 1, wherein the detection value includes a detection resistance value indicating a resistance of the device being probed.

4. The system of claim 3, wherein the control circuit is configured to determine that the short circuit condition is detected if the detection resistance value is less than a first predetermined resistance.

5. The system of claim 4, wherein the control circuit is configured to determine that the Network Interface Card is detected if the detection resistance value is in a range between the first predetermined resistance and a second predetermined resistance higher than the first predetermined resistance.

6. The system of claim 5, wherein the control circuit is configured to determine that an improper device is detected if the detection resistance value exceeds the second predetermined resistance.

7. A Power Sourcing Equipment (PSE) in a Power over Ethernet (PoE) system, comprising:

a probing circuit for determining a first response voltage produced in response to a first detection current supplied over an Ethernet link to a device being probed, and for determining a second response voltage produced in response to a second detection current supplied over the Ethernet link if the first response voltage is less that a threshold value, the second detection current being greater than the first detection current, and

a detection circuit responsive to the probing circuit to determine a detection resistance value indicating a resistance of the device being probed, the detection resistance value being defined by a difference between the second response voltage and the first response voltage,

the detection circuit being configured for determining that a short circuit condition is detected if the detection resistance value is in a first predetermined range, and determining that a Network Interface Card connected to the Ethernet link is detected if the resistance detection value is in a second predetermined range outside of the first predetermined range.

8. The PSE of claim 7, wherein the detection circuit is configured for determining that an improper device is detected if the detection resistance value is in a third predetermined range outside of the first and second predetermined ranges.

9. The PSE of claim 7, wherein the detection circuit is configured to determine that a short circuit condition is detected if the detection resistance value is less than a first predetermined resistance.

10. The PSE of claim 9, wherein the detection circuit is configured to determine that the Network Interface Card is detected if the detection resistance value is in a range between the first predetermined resistance and a second predetermined resistance higher than the first predetermined resistance.

11. The PSE of claim 10, wherein the detection circuit is configured to determine that the improper device is detected if the resistance detection value exceeds the second predetermined resistance.

12. A method of detecting a powered device (PD) in a Power over Ethernet (PoE) system, comprising the steps of:

producing a first detection signal supplied to a device being probed to determine a first response signal,

producing a second detection signal larger than the first detection signal if the first response signal is less than a threshold value,

determining a detection resistance value defined by a difference between a second response signal produced in response to the second detection signal, and the first response signal,

detecting a short circuit condition if the detection resistance value is less than a first predetermined resistance,

detecting a Network Interface Card if the detection resistance value is in a range between the first predetermined resistance and a second predetermined resistance higher than the first predetermined resistance; and

indicating a result of detection.

13. The method of claim 12, further comprising the step of detecting an improper device if the resistance detection value exceeds the second predetermined resistance.