THERMAL DE-RATING POWER SUPPLY FOR LED LOADS

• US 20140015447A1
• Filed: 03/13/2013
• Published: 01/16/2014
• Est. Priority Date: 07/10/2012
• Status: Active Grant

• Current Assignee: Dialog Semiconductor Incorporated (Renesas Electronics Corporation)
• Original Assignee: iWatt, Inc. (Renesas Electronics Corporation)
• Inventors: Shi, Fuqiang, Sha, Qiu, Gao, Xiaolin, Chen, Gordon
• Granted Patent: US 9,060,408 B2
• Time in Patent Office: Days
• US Class Current: 315/309
• CPC Class Codes: H05B 45/18 using temperature feedback
• CPC Class Codes: H05B 45/56 involving measures to prevent abnormal temperature of the LEDs

Abstract

Embodiments disclosed herein describe the use of a power supply to provide power to an LED load. The power supply provides a present output current to the LED, and receives a temperature signal representing the operating temperature of the LED. A target output current is determined, for instance based on the temperature signal. An output current rate of change is determined, and the power supply adjusts the output current to the LED at the determined rate of change until the output current is substantially equal to the target current.

Claims

1. A power supply comprising:

an analog-to-digital converter (“

ADC”

) configured to;

receive a temperature signal representing a temperature of a light-emitting diode (“

LED”

); and

generate a digital temperature signal based on the received temperature signal;

an over-temperature protection (“

OTP”

) circuit configured to;

receive the digital temperature signal;

detect an LED over-temperature condition based on the received digital temperature signal; and

generate a target output current for the LED based on the detected LED over-temperature condition;

a rate controller configured to;

receive the target output current; and

select a rate of change based on the received target output current; and

a driver circuit configured to;

provide the output current to the LED;

receive the rate of change; and

adjust the provided output current based on the received rate of change until the outputted current is substantially equal to the target output current.

2. The power supply of claim 1, wherein the temperature signal is received from a negative temperature coefficient resistor.

3. The power supply of claim 1, wherein the ADC comprises a 2-bit ADC.

4. The power supply of claim 1, wherein the LED over-temperature condition comprises the operation of the LED at a temperature over a pre-determined safe operation threshold.

5. The power supply of claim 1, wherein the target output current is less than a present output current.

6. The power supply of claim 1, wherein the rate of change comprises a maximum rate of change, and wherein adjusting the provided output current based on the received rate of change comprises adjusting the provided output current at a rate equal to or less than the rate of change.

7. The power supply of claim 1, wherein the rate of change comprises a minimum rate of change, and wherein adjusting the provided output current based on the received rate of change comprises adjusting the provided output current at a rate equal to or greater than the rate of change.

8. The power supply of claim 1, wherein the rate of change is selected such that the over-temperature condition is remedied within a pre-determined interval of time upon adjusting the provided output current at the rate of change.

9. The power supply of claim 1, wherein the rate of change is selected such that lighting artifacts are minimized when adjusting the provided output current at the rate of change.

10. A power supply comprising:

an ADC configured to generate a digital temperature signal representative of a temperature of an LED;

an OTP circuit configured to produce a target output current based on the digital temperature signal;

a rate controller configured to select an output current rate of change based on the produced target output current; and

a driver circuit configured to produce an output current for the LED, and to adjust the output current based on the rate of change.

11. The power supply of claim 10, wherein the rate of change comprises a maximum rate of change, and wherein adjusting the output current based on the rate of change comprises adjusting the produced output current at a rate equal to or less than the rate of change.

12. The power supply of claim 10, wherein the rate of change comprises a minimum rate of change, and wherein adjusting the output current based on the rate of change comprises adjusting the produced output current at a rate equal to or greater than the rate of change.

13. The power supply of claim 10, wherein a first rate of change is selected if the target output current is greater than a present output current, and wherein a second rate of change is selected if the target output current is less than a present output current.

14. The power supply of claim 13, wherein the first rate of change is different than the second rate of change.

15. A method of providing power to an LED, comprising:

detecting an over-temperature condition at the LED based on a temperature of the LED;

determining a target output current for the LED based on the detected over-temperature condition;

selecting an output current rate of change based on the determined target output current; and

adjusting a provided output current to the LED based on the selected output current rate of change.

16. The method of claim 15, wherein detecting an over-temperature condition at the LED comprises detecting a temperature of the LED over a pre-determined safe operation threshold of the LED.

17. The method of claim 15, wherein determining a target output current for the LED comprises determining a target output current that is less than a present output current to the LED.

18. The method of claim 15, wherein the output current rate of change is selected such that the over-temperature condition is remedied within a pre-determined interval of time upon adjusting the provided output current to the LED based on the rate of change.

19. The method of claim 15, wherein the output current rate of change is selected such that lighting artifacts are minimized upon adjusting the provided output current to the LED based on the rate of change.

20. A method of providing power to an LED, comprising:

providing a first output current to the LED;

determining a second output current for an LED based on a detected temperature of the LED;

selecting an output current rate of change based on the first and second output currents; and

adjusting the provided first output current to the LED at the selected output current rate of change until the provided first output current is equal to the second output current.