Voltage controlled backlight driver

• US 7,969,430 B2
• Filed: 02/19/2007
• Issued: 06/28/2011
• Est. Priority Date: 02/23/2006
• Status: Expired due to Fees

• Current Assignee: Polaris PowerLED Technologies, LLC (Microchip Technology Incorporated)
• Original Assignee: Microsemi Corp. - Analog Mixed Signal Group, Ltd. (Microchip Technology Incorporated)
• Inventors: Korcharz, Dror, Ferentz, Alon, Blaut, Roni, Peker, Arkadiy, Langer, Tamir
• Primary Examiner(s): Nguyen; Kevin M
• Assistant Examiner(s): BOYD, JONATHAN A
• Application Number:
  US11/676,313
• Publication Number:
  US 20070195025A1
• Time in Patent Office: 1,590 Days
• Field of Search: 315/246, 315/291, 315/299, 315/307, 315/308, 345/211, 345/212, 345/102
• US Class Current: 345/211
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/041 Temperature compensation
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2330/045 Protection against panel overheating
• CPC Class Codes: G09G 2330/08 Fault-tolerant or redundant circuits, or circuits in which repair of defects is prepared
• CPC Class Codes: G09G 2330/12 Test circuits or failure detection circuits included in a display system, as permanent part thereof
• CPC Class Codes: G09G 2360/14 Detecting light within display terminals, e.g. using a single or a plurality of photosensors
• CPC Class Codes: G09G 3/006 Electronic inspection or testing of displays and display drivers, e.g. of LED or LCD displays testing individual LED's G01R31/2635; testing lamps G01R31/44; testing of optical features of LCD displays G02F1/1309
• CPC Class Codes: G09G 3/3413 Details of control of colour illumination sources
• CPC Class Codes: G09G 3/342 using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
• CPC Class Codes: H05B 45/22 using optical feedback
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: H05B 45/58 involving end of life detection of LEDs

Abstract

A system for powering and controlling an LED backlight, the system comprising: a control circuitry; a controllable power source responsive to the control circuitry; and a plurality of LED strings receiving power from the controllable power source, the control circuitry being operative to control the output voltage of the controllable power source responsive to a function of an electrical characteristic of at least one of the plurality of LED strings.

Claims

1. A system for powering and controlling a light emitting diode (LED) light, the system comprising:

a control circuitry;

a controllable power source responsive to said control circuitry; and

a plurality of LED strings receiving power from said controllable power source,

said control circuitry arranged to control the output voltage of said controllable power source responsive to a selectable one of;

an electrical characteristic of the LED string of said plurality of LED strings exhibiting the lowest voltage drop;

an electrical characteristic of the LED string of said plurality of LED strings exhibiting the mean voltage drop;

an electrical characteristic of the LED string of said plurality of LED strings exhibiting the substantially arithmetic average voltage drop of said plurality of LED strings; and

the arithmetic average of the voltage drops of said plurality of LED strings.

2. A system according to claim 1, wherein said control circuitry is further arranged to determine the LED string of said plurality of LED strings exhibiting one of the lowest voltage drop and the mean voltage drop from among the plurality of LED strings.

3. A system according to claim 1, wherein said control circuitry is further arranged to calculate the arithmetic average voltage drop of the plurality of LED strings.

4. A system according to claim 1, further comprising a plurality of current limiters responsive to said control circuitry, each of said plurality of current limiters being associated with a particular one of said plurality of LED strings and arranged to limit the current flow there through.

5. A system according to claim 4, wherein said plurality of current limiters are arranged to limit current to a value responsive to an output of said control circuitry.

6. A system according to claim 4, wherein said control circuitry further comprises a pulse width modulator functionality in communication with each of said plurality of current limiters and operative to control the duty cycle of each of said plurality of LED strings.

7. A system according to claim 1, wherein said control circuitry further comprises a pulse width modulator functionality operative to control the duty cycle of each of said plurality of LED strings.

8. A system according to claim 7, further comprising a plurality of current limiters responsive to said control circuitry, each of said plurality of current limiters being associated with a particular one of said plurality of LED strings and arranged to limit the current flow there through, and wherein said control circuitry is further arranged to:

monitor said pulse width modulator functionality, and

in the event the duty cycle of said pulse width modulator functionality exceeds a predetermined maximum, adjust the current of at least one of said controllable current limiters so as to reduce the duty cycle of said pulse width modulator functionality while maintaining a predetermined luminance.

9. A system according to claim 8, wherein the adjustment of the current of said at least one of said controllable current limiters is by a predetermined amount.

10. A system according to claim 8, wherein said current is adjusted and the duty cycle of said pulse width modulator functionality is reduced so as to maintain said predetermined luminance while reducing the maximum duty cycle to a predetermined amount.

11. A system according to claim 8, wherein said current is adjusted and the duty cycle of said pulse width modulator functionality is reduced so as to maintain said predetermined luminance while reducing the maximum duty cycle by a predetermined amount.

12. A system according to claim 1, wherein said control circuitry is further operative to monitor an electrical characteristic of each of said plurality of LED strings and determine, responsive to said monitored electrical characteristic, if any of said plurality of LED strings exhibits an open circuit condition.

13. A system according to claim 12, wherein responsive to said determined open circuit condition, said control circuitry is further operative to adjust the current of at least one of the remaining LED strings by a predetermined amount to at least partially compensate for said determined open circuit condition.

14. A system according to claim 13, wherein said plurality of LED strings are arranged in a matrix such that said at least partial compensation maintains a substantially uniform color.

15. A method for powering and controlling a light emitting diode (LED) light, the method comprising:

providing a controllable power source;

providing a plurality of LED strings arranged to receive power in parallel from said provided controllable power source;

controlling said provided controllable power source responsive to a selectable one of;

an electrical characteristic of the LED string of said provided plurality of LED strings exhibiting the lowest voltage drop;

an electrical characteristic of the LED string of said provided plurality of LED strings exhibiting the mean voltage drop;

an electrical characteristic of the LED string of said provided plurality of LED strings exhibiting the substantially arithmetic average voltage drop of said provided plurality of LED strings; and

the arithmetic average voltage drop of said provided plurality of LED strings.

16. A method according to claim 15, further comprising:

determining the LED string of said provided plurality of LED strings exhibiting one of the lowest voltage drop and the mean voltage drop.

17. A method according to claim 15, further comprising:

calculating the arithmetic average voltage drop of said provided plurality of LED strings.

18. A method according to claim 15, further comprising:

pulse width modulating said provided plurality of LED strings so as to maintain at least one of a predetermined luminance and a predetermined white point.

19. A method according to claim 18, wherein said pulse width modulating is responsive to one of a color sensor and a photo-sensor.

20. A method according to claim 18, further comprising:

monitoring said pulse width modulating; and

in the event the duty cycle of said pulse width modulating exceeds a predetermined maximum,

increasing the current through at least one of said provided plurality of LED strings; and

reducing the duty cycle of said pulse width modulating so as to maintain said at least one of the predetermined luminance and the predetermined white point.

21. A method according to claim 20, wherein said increasing the current is by a predetermined amount.

22. A method according to claim 20, wherein said increasing the current is by an amount sufficient to reduce the duty cycle by a predetermined amount.

23. A method according to claim 20, wherein said increasing the current is by an amount sufficient to reduce the duty cycle to a predetermined amount.

24. A method according to claim 15, further comprising periodically monitoring each of said provided plurality of LED strings and determining if any of said provided plurality of LED strings exhibits an open circuit condition.

25. A method according to claim 24, further comprising in the event said determining determines that one of said plurality of LED strings exhibits an open circuit condition:

adjusting the current of at least one of the remaining LED strings by a predetermined amount to at least partially compensate for said LED string exhibiting said open circuit condition.

26. A method according to claim 25, further comprising:

arranging the provided plurality of LED strings in a matrix such that said at least partial compensation maintains a uniform color.