APPARATUS AND METHODS FOR DRIVING SOLID-STATE ILLUMINATION SOURCES

• US 20090303161A1
• Filed: 05/05/2009
• Published: 12/10/2009
• Est. Priority Date: 06/06/2008
• Status: Active Grant

• Current Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Original Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Inventors: Wallener, Damir, Messmer, Neil
• Granted Patent: US 8,994,615 B2
• Time in Patent Office: Days
• US Class Current: 345/55
• CPC Class Codes: G09G 2320/0271 Adjustment of the gradation levels within the range of the gradation scale, e.g. by redistribution or clipping
• CPC Class Codes: G09G 3/14 Semiconductor devices, e.g. diodes
• CPC Class Codes: G09G 3/2007 Display of intermediate tones
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: H05B 45/395 Linear regulators
• CPC Class Codes: H05B 45/397 Current mirror circuits
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A method for driving a solid-state illumination source to emit light having a brightness determined by a control value involves selecting a control mode based at least in part on the control value. In one embodiment a constant current is supplied to the solid-state illumination source for control values in a low range, a frequency-modulated (FM) current is supplied to the solid-state illumination source for control values in a mid range and a pulse-with modulation (PWM) current is supplied to the solid-state illumination source for control values in an upper range.

Claims

1. A method for controlling the brightness of light output by a solid-state illumination source, the method comprising:

obtaining a control value specifying a desired intensity of light to be emitted by the solid-state illumination source;

operating the solid-state illumination source in a constant current mode if the control value is within a first range;

operating the solid-state illumination source in a frequency modulation mode if the control value is within a second range greater than the first range; and

,

operating the solid-state illumination source in a pulse width modulation mode if the control value is within a third range greater than the second range.

2. A method according to claim 1 wherein a transition between the first range and the second range occurs at a first value when the solid-state illumination source is being operated in the frequency modulation mode or the pulse width modulation mode, and the transition between the first range and the second range occurs at a second value higher than the first value when the solid-state illumination source is being operated in the constant current mode.

3. A method according to claim 1 wherein a transition between the second range and the third range occurs at a third value when the solid-state illumination source is being operated in the pulse width modulation mode, and the transition between the second range and the third range occurs at a fourth value higher than the third value when the solid-state illumination source is being operated in the constant current mode or the frequency modulation mode.

4. A method according to claim 1 wherein operating the solid-state illumination device in the constant current mode comprises providing the solid-state illumination device with a constant current which is a function of the control value.

5. A method according to claim 4 wherein the constant current is a linear function of the control value.

6. A method according to claim 1 wherein operating the solid-state illumination device in the frequency modulation mode comprises providing the solid-state illumination device with pulses of current at a frequency which is a function of the control value.

7. A method according to claim 6 wherein the frequency is a linear function of the control value.

8. A method according to claim 6 wherein an amplitude of the pulses is a function of the control value.

9. A method according to claim 6 wherein a width of the pulses is a function of the control value.

10. A method according to claim 1 wherein operating the solid-state illumination device in the pulse width modulation mode comprises providing the solid-state illumination device with pulses of current each having a pulse width which is a function of the control value.

11. A method according to claim 10 wherein the pulse width is a linear function of the control value.

12. A method according to claim 10 wherein an amplitude of the pulses is a function of the control value.

13. A method according to claim 10 wherein a frequency of the pulses is a function of the control value.

14. A method according to claim 1 wherein operating the solid-state illumination device in the constant current mode, frequency modulation mode or pulse width modulation mode comprises operating the solid-state illumination source for a period equal to a frame cycle of a display incorporating the solid-state illumination source.

15. A method according to claim 1 comprising modifying start times of pulses of current in the frequency modulation mode or pulse width modulation mode with a random or pseudo-random factor that varies with time.

16. A method according to claim 1 comprising modifying a duty cycle of pulses of current in the frequency modulation mode or pulse width modulation mode with a random or pseudo-random factor that varies with time, and modifying amplitudes of the pulses with a complementary random or pseudo-random factor.

17. A method according to claim 1 wherein operating the solid-state illumination device in the frequency modulation mode comprises increasing a width of pulses of current as the control value increases.

18. A method according to claim 1 wherein operating the solid-state illumination device in the pulse width modulation mode comprises decreasing a frequency of pulses of current as the control value increases.

19. A method according to claim 1 comprising superimposing current pulses on a continuous current background when operating the solid-state illumination source in the frequency modulation mode if the control value is within a predetermined amount of a transition between the first range and the second range.

20. A method according to claim 19 wherein the continuous current background decreases as the control value increases.

21. A method according to claim 1 wherein operating the solid-state illumination source in the frequency modulation mode comprises selecting a frequency of pulses which exceeds a reciprocal of a thermal time constant of the solid-state illumination source.

22. A method according to claim 1 wherein operating the solid-state illumination source in the pulse width modulation mode comprises maintaining gaps between adjacent pulses shorter than a thermal time constant of the solid-state illumination source.

23. A method according to claim 1 comprising adjusting a transition between the first range and the second range or a transition between the second range and the third range based on a temperature of the solid-state illumination source.

24. A method according to claim 1 comprising adjusting a transition between the first range and the second range or a transition between the second range and the third range based on a status of a power supply for the solid-state illumination source.

25. A method for controlling the brightness of light output by a solid-state illumination source, the method comprising:

obtaining a control value specifying a desired intensity of light to be emitted by the solid-state illumination source;

operating the solid-state illumination source in a constant current mode if the control value is less than a first reference value;

operating the solid-state illumination source in a frequency modulation mode if the control value is greater than or equal to the first reference value and less than a second reference value; and

,

operating the solid-state illumination source in a pulse width modulation mode if the control value is greater than or equal to the second reference value.

26. A method according to claim 25 comprising:

comparing the received control value to an immediately preceding control value;

increasing the first and second reference values if the received control value is greater than the immediately preceding control value; and

,

decreasing the first and second reference values if the received control value is less than the immediately preceding control value.

27. A method according to claim 25 comprising superimposing current pulses on a continuous current background when operating the solid-state illumination source in the frequency modulation mode if the control value is within a predetermined amount of the first reference value.

28. A method according to claim 27 wherein the continuous current background decreases as the control value increases.

29. A method according to claim 25 wherein operating the solid-state illumination source in the frequency modulation mode comprises selecting a frequency of pulses which exceeds a reciprocal of a thermal time constant of the solid-state illumination source.

30. A method according to claim 25 wherein operating the solid-state illumination source in the pulse width modulation mode comprises maintaining gaps between adjacent pulses shorter than a thermal time constant of the solid-state illumination source.

31. A driver for controlling a solid-state illumination source to emit light, the driver comprising:

an input configured to receive a control value specifying a desired intensity of light to be emitted by the solid-state illumination source;

an output connectable to control electrical current in the solid-state illumination source;

at least one comparison unit configured to compare the control value with a first reference value and a second reference value;

a constant-current driver configured to control the electrical current to have a constant value corresponding to the control value if the control value is less than the first reference value;

a frequency-modulation driver configured to control the electrical current to have pulses at a frequency corresponding to the control value if the control value is between the first and second reference values; and

,

a pulse-width-modulation driver configured to control the electrical current to have pulses having widths corresponding to the control value if the control value exceeds the second reference value.

32. A method for controlling the brightness of light output by a light emitting diode, the method comprising:

obtaining a control value specifying a desired intensity of light to be emitted by the light emitting diode;

comparing the control value with a reference value;

operating the light emitting diode in a first mode if the control value is less than the reference value; and

,

operating the light emitting diode in a second mode if the control value is greater than the reference value.

33. A method for controlling the brightness of light output by a light emitting diode, the method comprising:

receiving a control value specifying a desired intensity of light to be emitted by the light emitting diode;

operating the light emitting diode in a first mode if the control value is less than a first reference value;

operating the light emitting diode in a second mode if the control value is greater than the first reference value and less than a second reference value; and

,

operating the light emitting diode in a third mode if the control value is greater than the second reference value.

34. A display comprising:

an array of solid-state illumination sources; and

,

a driver configured to control the solid-state illumination sources, the driver comprising;

inputs connectable to receive control values specifying desired intensities of light to be emitted by the solid-state illumination sources;

outputs connectable to control electrical currents in the solid-state illumination sources;

a constant-current driver configured to control the electrical current of each solid-state illumination sources having a control value within a first range to have a constant value corresponding to the control value;

a frequency-modulation driver configured to control the electrical current of each solid-state illumination sources having a control value within a second range greater than the first range to have pulses at a frequency corresponding to the control value; and

,

a pulse-width-modulation driver configured to control the electrical current of each solid-state illumination sources having a control value within a third range greater than the second range to have pulses having widths corresponding to the control value.

35. A display according to claim 34 wherein the control values are based on image data specifying a desired image.

36. A display according to claim 35 wherein the control value of each solid-state illumination source is based on a position of that solid-state illumination source.

37. A display according to claim 34 wherein the each solid-state illumination source is individually controllable.

38. A display according to claim 34 wherein the solid-state illumination sources comprise a plurality of groups of solid-state illumination sources, and wherein each group of solid-state illumination sources is individually controllable.

39. A display according to claim 38 wherein each group of solid-state illumination sources comprises a plurality of series-connected light emitting diodes.

40. A method of displaying an image on a display comprising an array of light emitting diodes, the method comprising:

obtaining image data specifying a desired image;

processing the image date to obtain a control values for each light emitting diode of the array of light emitting diodes;

operating light emitting diodes having control values within a first range in a constant current mode

operating light emitting diodes having control values within a second range greater than the first range in a frequency modulation mode; and

,

operating light emitting diodes having control values within a third range greater than the second range in a pulse width modulation mode.

41. A driver for controlling a solid-state illumination source to emit light, the driver comprising:

input means for receiving a control value specifying a desired intensity of light to be emitted by the solid-state illumination source;

output means for controlling electrical current in the solid-state illumination source;

comparison means for comparing the control value with a first reference value and a second reference value;

constant-current driver means for controlling the electrical current to have a constant value corresponding to the control value if the control value is less than the first reference value;

frequency-modulation driver means for controlling the electrical current to have pulses at a frequency corresponding to the control value if the control value is between the first and second reference values; and

,

pulse-width-modulation driver means for controlling the electrical current to have pulses having widths corresponding to the control value if the control value exceeds the second reference value.

42. A display comprising:

arrayed illumination means for emitting light; and

,

driver means for controlling the illumination means, the driver means comprising;

input means for receiving control values specifying desired intensities of light to be emitted by the solid-state illumination sources;

output means for controlling electrical currents in the illumination means;

constant-current driver means for controlling the electrical current of each of the illumination means having a control value within a first range to have a constant value corresponding to the control value;

frequency-modulation driver means for controlling the electrical current of each of the illumination means having a control value within a second range greater than the first range to have pulses at a frequency corresponding to the control value; and

,

pulse-width-modulation driver means for controlling the electrical current of each of the illumination means having a control value within a third range greater than the second range to have pulses having widths corresponding to the control value.