DYNAMIC CURRENT LIMITS

• US 20090121548A1
• Filed: 11/08/2007
• Published: 05/14/2009
• Est. Priority Date: 11/08/2007
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: Vetteth, Anoop, Schindler, Frederick R.
• Granted Patent: US 7,902,694 B2
• Time in Patent Office: Days
• US Class Current: 307/39
• CPC Class Codes: H02J 1/04 Constant-current supply systems
• CPC Class Codes: H02J 1/14 Balancing the load in a network
• CPC Class Codes: H04L 12/10 Current supply arrangements

Abstract

A method is provided for allocating and providing power to network devices. The method includes (i) receiving an electronic request to power a network device with a requested amount of power, (ii) establishing a worst-case current draw of the device in the event of a pre-defined maximum voltage slew rate, and (iii) selectively (a) allocating and providing power to the device when a remaining power capacity is greater than or equal to a provision voltage multiplied by the worst-case current draw of the device in the event of the maximum voltage slew rate, and (b) denying power to the device when the remaining power capacity is less than the provision voltage multiplied by the worst-case current draw of the device in the event of the maximum voltage slew rate. Apparatus are also provided for performing the method.

Claims

1. A method comprising:

receiving an electronic request to power a network device with a requested amount of power;

establishing a worst-case current draw of the device in the event of a pre-defined maximum voltage slew rate;

allocating and providing power to the device when a remaining power capacity is greater than or equal to a provision voltage multiplied by the worst-case current draw of the device in the event of the maximum voltage slew rate; and

denying power to the device when the remaining power capacity is less than the provision voltage multiplied by the worst-case current draw of the device in the event of the maximum voltage slew rate.

2. A method as in claim 1 wherein establishing the worst-case current draw of the device in the event of the pre-defined maximum voltage slew rate includes summing together the following amounts:

the requested amount of power divided by the provision voltage; and

a capacitance of a capacitor within the device multiplied by the maximum voltage slew rate.

3. A method as in claim 2 wherein the pre-defined maximum voltage slew rate is 200 volts per second.

4. A method as in claim 2 wherein the capacitance of the capacitor within the device is assumed to be a pre-determined value.

5. A method as in claim 2 wherein the method further comprises:

receiving a signal from the device indicating the capacitance of the capacitor within the device.

6. A method as in claim 1 wherein:

the method further includes;

calculating a current limit for the device, wherein calculating the current limit for the device includes establishing a maximum amount of current the device is capable of drawing in the event that voltage remains substantially constant, and adding a provision tolerance to that maximum amount; and

substantially limiting the total amount of current capable of being provided to the device to the calculated current limit for the device; and

establishing the worst-case current draw of the device in the event of the maximum voltage slew rate includes calculating as the worst-case current draw of the device in the event of the maximum voltage slew rate a number which is less than or equal to the calculated current limit for the device.

7. A method as in claim 6 wherein establishing the maximum amount of current the device is capable of drawing in the event that voltage remains substantially constant includes:

establishing that the maximum amount of current the device is capable of drawing in the event that voltage remains substantially constant is the requested amount of power divided by the provision voltage multiplied by a burst factor, the burst factor being a number in the range of 1.0 to 1.15.

8. A method as in claim 6 wherein establishing the maximum amount of current the device is capable of drawing in the event that voltage remains substantially constant includes:

establishing that the maximum amount of current the device is capable of drawing in the event that voltage remains substantially constant is the largest amount of current that the device is configured to be able to request under any circumstances.

9. A method as in claim 6 wherein adding the provision tolerance to the maximum amount includes:

adding the provision tolerance, the provision tolerance being equal to a percentage of the maximum amount of current the device is capable of drawing in the event that voltage remains substantially constant, the percentage being in the range of 0% to 20%.

10. An apparatus comprising:

a network interface;

a power supply, the power supply including a capacitor having a capacitance; and

a controller coupled to the network interface, the controller being configured to;

send a request to power sourcing equipment, over the network interface, to be provided a particular amount of power over the network interface, the power to be provided to the power supply; and

report, over the network interface, the capacitance to the power sourcing equipment.

11. An apparatus as in claim 10 wherein the apparatus further includes a current limiting device to limit the amount of current that can be received at the network interface to a current limit.

12. An apparatus as in claim 11 wherein the current limit is set to a pre-programmed value, the pre-programmed value being the largest amount of power that the apparatus is configured to be capable of requesting under any circumstances divided by the provision voltage plus a provision tolerance.

13. An apparatus as in claim 11 wherein the controller is further configured to:

calculate a maximum amount of current the apparatus is capable of drawing in the event that voltage remains substantially constant; and

send a signal to the current limiting device instructing the current limiting device to set the current limit to be the calculated maximum amount of current the apparatus is capable of drawing in the event that voltage remains substantially constant plus a provision tolerance, the provision tolerance being equal to a percentage of the calculated maximum amount of current the device is capable of drawing in the event that voltage remains substantially constant, the percentage being in the range of 0% to 20%.

14. An apparatus as in claim 13 wherein the controller is configured to, when calculating the maximum amount of current the apparatus is capable of drawing in the event that voltage remains substantially constant, calculate that value to be a particular amount of power that the apparatus has requested divided by the provision voltage multiplied by a burst factor, the burst factor being a number in the range of 1.0 to 1.15.

15. An apparatus comprising:

a power supply having a provision voltage and a remaining power capacity;

a network interface; and

a controller coupled to the network interface, the controller being configured to;

receive, over the network interface, a request to power a device over the network interface with a requested amount of power;

establish a worst-case current draw of the device in the event of a pre-defined maximum voltage slew rate;

allocate and provide power to the device from the power supply over the network interface when the remaining power capacity is greater than or equal to the provision voltage multiplied by the worst-case current draw of the device in the event of the maximum voltage slew rate; and

deny power to the device when the remaining power capacity is less than the provision voltage multiplied by the worst-case current draw of the device in the event of the maximum voltage slew rate.

16. An apparatus as in claim 15 wherein the controller, when establishing the worst-case current draw of the device in the event of the maximum voltage slew rate, is operable to sum together the following amounts:

the requested amount of power divided by the provision voltage; and

a capacitance of a capacitor within the device multiplied by the maximum voltage slew rate.

17. An apparatus as in claim 16 wherein the controller is further configured to receive from the device, via the network interface, a signal indicating the capacitance of the capacitor within the device.

18. An apparatus as in claim 15 wherein:

the controller is further configured to;

calculate a current limit for the device, wherein calculating the current limit for the device includes establishing a maximum amount of current the device is capable of drawing in the event that voltage remains substantially constant, and adding a provision tolerance to that maximum amount; and

substantially limit the total amount of current capable of being provided to the device to the calculated current limit for the device; and

the controller, when establishing the worst-case current draw of the device in the event of the maximum voltage slew rate, is operable to calculate, as the worst-case current draw of the device in the event of the maximum voltage slew rate, a number which is less than or equal to the calculated current limit for the device.

19. An apparatus as in claim 18 wherein the controller, when determining the maximum amount of current the device is capable of drawing in the event that voltage remains substantially constant, is operable to:

establish that the maximum amount of current the device is capable of drawing in the event that voltage remains substantially constant is the requested amount of power divided by the provision voltage multiplied by a burst factor, the burst factor being a number in the range of 1.0 to 1.15.

20. An apparatus as in claim 15 wherein:

the power supply is an uninterruptible supply having a first power source and a second power source; and

the pre-defined maximum voltage slew rate is equal to the largest voltage slew rate of the power supply that could be caused by one or more power sources failing.