HIGH CRI WHITE LIGHT EMITTING DEVICES AND DRIVE CIRCUITRY

• US 20110115406A1
• Filed: 11/12/2010
• Published: 05/19/2011
• Est. Priority Date: 11/19/2009
• Status: Active Grant

• Current Assignee: Intematix Corporation
• Original Assignee: Intematix Corporation
• Inventors: Wang, Gang, Li, Yi-Qun
• Granted Patent: US 8,779,685 B2
• Time in Patent Office: Days
• US Class Current: 315/294
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/73265 Layer and wire connectors
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/395 Linear regulators
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A high CRI white light emitting device comprises: a blue solid state light emitter (LED) operable to generate blue light; a phosphor material operable to absorb a portion of the blue light and to emit green/yellow light and a red solid state light emitter (LED) operable to generate red light. The emission product of the device comprises the combined light generated by the blue and red LEDs and green/yellow light generated by the phosphor material and appears white in color. The device further comprises a drive circuit operable to compensate for variation in the ratio (relative contribution) of red to blue light in the emission product such as to ensure that said variation is less than 20% over an operating temperature range of at least 25° C. The drive circuit can reduce variation in the CRI and CCT of the device'"'"'s emission product over the operating temperature range.

Claims

1. A white light emitting device comprising:

at least one blue solid state light emitter operable to generate blue light with a dominant wavelength in a range 400 nm to 480 nm;

at least one phosphor material operable to absorb a portion of the blue light and to emit light with a dominant wavelength in a range 490 nm to 590 nm; and

at least one red solid state light emitter operable to generate red light with a dominant wavelength in a range 600 nm to 700 nm;

wherein the emission product of the device comprises the combined light generated by the blue and red light emitters and light generated by the at least one phosphor material and appears white in color; and

a drive circuit operable to compensate for variation in the ratio of red to blue light in the emission product such that over an operating temperature range of at least 25°

C. said variation is less than 20%.

2. The device of claim 1, wherein the drive circuit is configured such that in operation over the operating temperature range said variation is selected from the group consisting of being:

less than 10%, less than 5% and less than 1%.

3. The device of claim 1, wherein the drive circuit is configured for operation over an operating temperature range selected from the group consisting of being:

at least 25°

C., at least 50°

C. and at least 100°

C.

4. The device of claim 1, and configured such that the emission product has a color rendering index selected from the group consisting of being:

at least 80, at least 85, at least 90 and at least 95.

5. The device of claim 1, wherein the drive circuit is operable to control the power of at least one of the red and blue light emitters in response to a parameter related to the operating temperature of at least one of the blue and red light emitters.

6. The device of claim 5, wherein the parameter comprises a temperature of at least one of the blue and red light emitters.

7. The device of claim 6, and further comprising a sensor for sensing the temperature of the red and/or blue light emitters.

8. The device of claim 7, wherein the blue and red light emitters are mounted in thermal communication with a thermally conductive substrate and wherein the sensor is configured to sense the temperature of the substrate.

9. The device of claim 6, and comprising respective sensors for sensing the temperature of the blue and red light emitters.

10. The device of claim 7, wherein the sensor comprises a temperature dependent resistor.

11. The device of claim 7, wherein at least one of the blue and red light emitters is connected in series with the temperature dependent resistor and said light emitter is operable from a constant voltage source.

12. The device of claim 11, wherein the temperature dependent resistor has a negative temperature coefficient and is connected in series with the at least one red light emitter.

13. The device of claim 11, wherein the temperature dependent resistor has a positive temperature coefficient and is connected in series with the at least one blue light emitter.

14. The device of claim 11 wherein the blue and red light emitter are connected in series with a respective temperature dependent resistor.

15. The device of claim 7, wherein at least one of the blue and red emitters is connected in parallel with the temperature dependent resistor and said light emitter is operable from a constant current source.

16. The device of claim 15, wherein the temperature dependent resistor has a positive temperature coefficient and is connected in parallel with the at least one red light emitter.

17. The device of claim 15, wherein the temperature dependent resistor has a negative temperature coefficient and is connected in parallel with the at least one blue light emitter.

18. The device of claim 15 wherein the blue and red light emitter are connected in parallel with a respective temperature dependent resistor.

19. The device of claim 10, wherein the blue and red light emitters are connected in parallel and driven from a constant current source and wherein the temperature dependent resistor has a negative temperature coefficient and is connected in series with the at least one red light emitter and configured such that in operation the drive current of the at least one red light emitter increases relative to the drive current of the at least one blue light emitter with increasing temperature.

20. The device of claim 10, wherein the blue and red light emitters are connected in parallel and driven from a constant current source and wherein the temperature dependent resistor has a positive temperature coefficient and is connected in series with the at least one blue light emitter and configured such that in operation the drive current of the at least one blue light emitter decreases relative to the drive current of the at least one red light emitter with increasing temperature.

21. The device of claim 10, wherein the blue and red light emitters are connected in parallel and driven from a constant current source and comprising a respective temperature dependent resistor connected in series with the blue and red light emitters.

22. The device of claim 6, wherein the drive circuit is operable to control the drive current of one or both light emitters in dependence on a difference between a measured temperature and a reference temperature.

23. The device of claim 22, wherein the drive circuit comprises a comparator operable to compare the measured and reference temperatures.

24. The device of claim 1, wherein the parameter comprises the forward drive voltage of at least one of the blue and red light emitters.

25. The device of claim 24, wherein the drive circuit is operable to control the drive current of one or both light emitters in dependence on a difference between a drive voltage and a reference voltage.

26. The device of claim 25, wherein the drive circuit comprises a comparator operable to compare the measured and reference voltages.

27. The device of claim 24, wherein the drive circuit is operable to control the drive current in dependence on a difference of forward drive voltages of the blue and red light emitters.

28. The device of claim 1, wherein the at least one phosphor material is physically separated from the at least one blue LED by a distance of at least 5 mm.

29. A white light emitting device comprising:

at least one blue LED operable to generate blue light;

at least one phosphor material operable to absorb a portion of the blue light and to emit green/yellow light; and

at least one red LED operable to generate red light;

wherein the emission product of the device comprises the combined light generated by the blue and red light LEDs and green/yellow light generated by the at least one phosphor material and appears white in color; and

a drive circuit operable to compensate for variation in the ratio of red to blue light in the emission product such that over an operating temperature range of at least 25°

C. said variation is less than 20%.