Methods and apparatus for controlling series-connected LEDs

• US 7,781,979 B2
• Filed: 11/09/2007
• Issued: 08/24/2010
• Est. Priority Date: 11/10/2006
• Status: Active Grant

• Current Assignee: Signify North America Corporation (Signify N.V.)
• Original Assignee: Philips Solid-State Lighting Solutions (Koninklijke Philips N.V.)
• Inventors: Lys, Ihor A.
• Primary Examiner(s): VO, TUYET THI
• Application Number:
  US11/938,051
• Publication Number:
  US 20080122376A1
• Time in Patent Office: 1,019 Days
• Field of Search: 315/185.S, 315/200.A, 315/291, 315307-311, 315/247, 315/246, 315312-324, 345/82, 345/102, 345211-214, 345/204
• US Class Current: 315/185.00S
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices

Abstract

Methods and apparatus for controlling series-connected LEDs. Two or more LEDs are connected in series between a first node and a second node, wherein a series current flows between the nodes when an operating voltage is applied across the nodes. One or more controllable current paths are connected in parallel with at least a first LED for at least partially diverting the series current around at least the first LED. A controller monitors at least one parameter representative of the operating voltage, determines a maximum number of the series-connected LEDs that can be energized by the operating voltage, and controls the controllable current path(s) so as to increase an amount of the series current that is diverted around at least the first LED when the maximum number is less than a total number of all of the LEDs connected in series. In one example, the foregoing may be implemented as an integrated circuit package to provide a lighting apparatus suitable for automotive applications.

Claims

1. An apparatus, comprising:

at least two LEDs connected in series between a first node and a second node, wherein a series current flows between the first node and the second node when an operating voltage is applied across the first node and the second node;

at least one controllable current path connected in parallel with at least a first LED of the at least two LEDs for at least partially diverting the series current around the first LED; and

at least one controller for monitoring at least one parameter representative of the operating voltage and determining a maximum number of LEDs of the at least two LEDs that can be energized by the operating voltage, the at least one controller controlling the at least one controllable current path so as to increase an amount of the series current that is diverted around at least the first LED when the maximum number is less than a total number of all of the at least two LEDs connected in series.

2. The apparatus of claim 1, wherein the at least one controller controls the at least one controllable current path so as to increase the amount of the series current that is diverted around the first LED when the at least one parameter indicates that the operating voltage is less than a predetermined threshold value, and wherein the predetermined threshold value represents a minimum operating voltage necessary to energize all of the at least two LEDs.

3. The apparatus of claim 1, wherein the at least one controller controls the at least one controllable current path to substantially divert the series current around the first LED so as to short circuit the first LED.

4. The apparatus of claim 1, wherein:

the at least two LEDs include at least three LEDs connected in series between the first node and the second node; and

the at least one controllable current path includes a plurality of controllable current paths responsive to the at least one controller, each current path connected in parallel with at least one of the at least three LEDs.

5. The apparatus of claim 4, wherein the at least three LEDs includes a first number of LEDs, wherein the plurality of controllable current paths includes a second number of controllable current paths, and wherein the first number and the second number are different.

6. The apparatus of claim 4, wherein the at least three LEDs includes a first number of LEDs, wherein the plurality of controllable current paths includes a second number of controllable current paths, wherein the first number and the second number are the same, and wherein each current path is connected in parallel with a corresponding one of the at least three LEDs.

7. The apparatus of claim 4, wherein the at least one controller controls at least some of the plurality of controllable current paths, and wherein each controllable current path controlled by the controller intermittently diverts the series current around the corresponding at least one of the at least three LEDs, such that less than all of the at least three LEDs are simultaneously energized.

8. The apparatus of claim 7, wherein the at least one controller sequentially controls the at least some of the plurality of controllable current paths.

9. The apparatus of claim 7, wherein the at least one controller simultaneously controls at least two of the at least some of the plurality of controllable current paths.

10. The apparatus of claim 1, further comprising a current source, connected in series with the at least two LEDs between the first node and the second node, for setting the series current.

11. The apparatus of claim 10, wherein the current source is configured to set the series current based on the operating voltage.

12. The apparatus of claim 10, wherein the current source is responsive to the at least one controller, and wherein the at least one controller controls the series current based at least in part on the monitored at least one parameter representative of the operating voltage.

13. The apparatus of claim 12, wherein the at least one controller is configured to control the current source so as to increase the series current as the operating voltage decreases.

14. The apparatus of claim 12, wherein the at least one controller is configured to control the current source so as to duty cycle modulate the series current based at least in part on the monitored at least one parameter representative of the operating voltage.

15. A method of energizing a plurality of LEDs connected in series between a first node and a second node, wherein a series current flows between the first node and the second node when an operating voltage is applied across the first node and the second node, the method comprising:

A) monitoring at least one parameter representative of the operating voltage;

B) determining a maximum number of LEDs of the at least two LEDs that can be energized by the operating voltage; and

C) when the maximum number is less than a total number of all of the at least two LEDs connected in series, shorting out at least one of the plurality of LEDs so that less than all of the plurality of LEDs are simultaneously energized.

16. The method of claim 15, wherein C) comprises successively energizing different ones of the plurality of LEDs, or different groupings of less than all of the plurality of LEDs.

17. An apparatus, comprising:

a plurality of LEDs connected in series between a first node and a second node, wherein a series current flows between the first node and the second node when an operating voltage is applied across the first node and the second node;

a plurality of controllable current paths, each current path connected in parallel with a corresponding one of the plurality of LEDs for diverting the series current around the corresponding one of the plurality of LEDs;

a current source connected in series with the plurality of LEDs between the first node and the second node for setting the series current; and

at least one controller for monitoring at least one parameter related to the operating voltage and for intermittently controlling the plurality of controllable current paths so as to divert the series current around respective corresponding ones of the plurality of LEDs in a timed sequence when the at least one monitored parameter indicates that the operating voltage is less than a predetermined threshold value, such that less than all of the plurality of LEDs are simultaneously energized.

18. The apparatus of claim 17, wherein the at least one controller is configured to control the current source to increase the series current so as to maintain an essentially constant brightness of light generated by the plurality of LEDs when the operating voltage falls below the predetermined threshold value.

19. The apparatus of claim 17, wherein:

the plurality of LEDs includes at least one first LED for generating first radiation having a first spectrum, and at least one second LED for generating second radiation having a second spectrum different than the first spectrum; and

the at least one controller controls the plurality of controllable current paths in a predetermined manner based at least in part on the different spectrums of the plurality of LEDs.

20. The apparatus of claim 19, wherein:

the at least one first LED includes at least one first white LED, such that the first spectrum corresponds to a first color temperature;

the at least one second LED includes at least one second white LED, such that the second spectrum corresponds to a second color temperature different than the first color temperature; and

the at least one controller controls the plurality of controllable current paths such that an overall color temperature of the light generated by the plurality of LEDs, based on at least one of the first spectrum and the second spectrum, decreases as the operating voltage falls below the predetermined threshold value.

21. An automotive lighting apparatus, comprising:

at least one integrated circuit chip, comprising;

a first number of LEDs connected in series between a first node and a second node, wherein a series current flows between the first node and the second node when an operating voltage is applied across the first node and the second node;

a second number of controllable current paths, wherein the second number is equal to or less than the first number, each current path connected in parallel with a corresponding one of the first number LEDs for diverting the series current around the corresponding one of the first number of LEDs;

a current source connected in series with the first number of LEDs between the first node and the second node for setting the series current; and

at least one controller for monitoring at least one parameter representative of the operating voltage and determining a maximum number of LEDs of the first number of LEDs that can be energized by the operating voltage, the at least one controller controlling the second number of controllable current paths so as to divert the series current around respective corresponding ones of the first number of LEDs when the maximum number is less than the first number, such that less than all of the first number of LEDs are simultaneously energized; and

a package for the at least one integrated circuit chip, the package including at least one first electrical connector configured to mate with a complimentary electrical connector or wire harness of an automobile, the at least one first electrical connector including at least a first lead electrically connected to the first node and a second lead electrically connected to the second node for applying the operating voltage across the first node and the second node.

22. The apparatus of claim 21, wherein the first number is four.

23. The apparatus of claim 21, wherein the at least one controller includes at least one communication port for receiving and/or transmitting information, and wherein the at least one first electrical connector includes at least a third lead electrically connected to the at least one communication port.

24. The apparatus of claim 23, wherein the at least one controller controls the second number of controllable current paths based at least in part on first information received by the at least one communication port via the third lead, and wherein the first information relates to an external condition associated with the automobile.

25. The apparatus of claim 23, wherein the at least one controller includes at least one memory to store second information, and wherein the at least one controller transmits at least some of the second information from the at least one communication port via the third lead.