Circuit topology for driving high-voltage LED series connected strings

Patent metadata

Field	Value
Publication number	US-9860946-B2
Application number	US-57842409-A
Country	US
Kind code	B2
Filing date	Oct 13, 2009
Priority date	Jun 15, 2009
Publication date	Jan 2, 2018
Grant date	Jan 2, 2018

Abstract

A system for backlighting a display uses an open or closed loop and small components that are well suited to high-frequency applications. The system includes multiple LED strings, a high-voltage source, and a low-voltage regulator that has a polarity opposite to that of the high-voltage source. The high-voltage source and the low-voltage regulator provide voltage differences across the LED strings to illuminate them. In one embodiment, the high-voltage source is about 200 VDC, and the low-voltage regulator produces voltages between −2 VDC and −30 VDC. Many types of displays, such as those used on LCD televisions and LCD personal computers, can be backlit in accordance with the embodiments.

First claim

I claim:

1. A backlighting system comprising:
one or more LED strings;
a high-voltage source;
one or more low-voltage regulators coupled in a feedback loop, the one or more low-voltage regulators have a polarity opposite that of the high-voltage source, the high-voltage source and the one or more low-voltage regulators provide voltage differences across the one or more LED strings to illuminate the one or more LED strings without a current source, the one or more low-voltage regulators are programmed to periodically couple outputs of the one or more LED strings to a controlled and variable low voltage.

2. The backlighting system of claim 1 , wherein a voltage of the high-voltage source is a factor of −5 to −20 times a voltage of the controlled and variable low voltage.

3. The backlighting system of claim 1 , further comprising one or more controllers each controlling a current through one of the one or more LED strings.

4. The backlighting system of claim 3 , further comprising one or more sample-and-hold circuits each coupling an output of one of the one or more LED strings to one of the one or more controllers.

5. The backlighting system of claim 1 , wherein the one or more LED strings, the high-voltage source, and the one or more low-voltage regulators form an open-loop system.

6. The backlighting system of claim 1 , further comprising a boost converter, wherein the boost converter, the one or more low-voltage regulators, and the high-voltage source form an adaptive loop configured to generate a voltage on the high-voltage source from a smallest of the voltages from the one or more low-voltage regulators.

7. The backlighting system of claim 1 , wherein the one or more low-voltage regulators and the high-voltage source form a closed adaptive loop to minimize the voltage on the one or more low voltage regulators.

8. An electronic device comprising:
a display; and
a backlighting system positioned to backlight the display, the backlighting system comprising:
one or more LED strings;
a high-voltage source;
a low-voltage regulator coupled in a feedback loop, the low-voltage regulator having a polarity opposite that of the high-voltage source, the high-voltage source comprises a DC voltage and is coupled to a controlled and variable DC voltage having a magnitude smaller than that of the DC voltage, the high-voltage source and the low-voltage regulator provide voltage differences across the one or more LED strings to illuminate the one or more LED strings without a current source.

9. The electronic device of claim 8 , wherein an absolute value of a voltage of the high-voltage source is at least 100 VDC and an absolute value of a voltage on the low-voltage regulator is between 2 VDC and 30 VDC.

10. The electronic device of claim 8 , wherein the one or more LED strings, the high-voltage source, and the low-voltage regulator form an open-loop system.

11. The electronic device of claim 8 , wherein the electronic device is a liquid crystal display (LCD) television or an LCD personal computer.

12. A method of controlling the brightness of multiple LED strings comprising:
sensing currents through multiple LED strings generated by voltage sources having opposite polarities;
adjusting the currents to maintain a brightness of the LED strings within a predetermined range by periodically coupling outputs of the LED strings to controlled and variable low voltages generated by a low voltage regulator.

13. The method of claim 12 , wherein adjusting the currents comprises adjusting duty cycles of the currents.

14. The method of claim 12 , wherein an absolute value of one of the voltage sources is at least 100 VDC, and an absolute value of another of the voltage sources is between 2 VDC and 30 VDC.

15. The method of claim 14 , further comprising adapting one of the voltage sources based on a voltage on another of the voltage sources to adjust the brightness of the multiple LEDs.

16. The method of claim 12 , further comprising using the multiple LED strings to backlight a display of an electronic device.

17. The method of claim 16 , wherein the electronic device is a liquid crystal display (LCD) television or an LCD personal computer.

18. The method of claim 12 , wherein the multiple LED strings and the voltage sources form an open loop.

19. A backlighting system comprising:
one or more low-voltage regulators coupled in a feedback loop, the one or more low-voltage regulators have a polarity opposite that of a high-voltage source for powering one or more LED strings without a current source, the one or more low-voltage regulators control a low-voltage source to provide voltage differences across the one or more LED strings to illuminate the one or more LED strings, and the one or more low-voltage regulators are programmed to periodically couple outputs of the one or more LED strings to one or more controlled and variable low voltages.

20. The backlighting system of claim 19 , further comprising one or more controllers each for maintaining a current through one of the one or more LED strings within a predetermined range.

21. The backlighting system of claim 20 , further comprising one or more sample-and-hold circuits each for coupling an output of one of the one or more LED strings to one of the one or more controllers.

22. The backlighting system of claim 19 , wherein a voltage of the high-voltage source is a factor of −5 to −20 times a voltage of the low-voltage source.

23. The backlighting system of claim 20 , wherein each of the one or more controllers is also configured to charge a capacitor through an inductor to generate a voltage applied to a corresponding one of the one or more LED strings.

24. The backlighting system of claim 19 , wherein the one or more LED strings and the one or more low-voltage regulators are for forming an open-loop system with the high-voltage source.

25. The backlighting system of claim 19 , further comprising a boost converter, wherein the boost converter and the one or more low-voltage regulators are for forming an adaptive loop with the high-voltage source.

26. The backlighting system of claim 19 , wherein the one or more low-voltage regulators are for forming an adaptive loop with the high-voltage source to minimize voltages on the one or more low-voltage regulators.

27. The backlighting system of claim 19 , wherein the one or more LED strings are for backlighting a display of an electronic device.

28. The backlighting system of claim 27 , wherein the electronic device is a liquid crystal display (LCD) television or an LCD personal computer.

29. A current regulator comprising:
a low-voltage regulator coupled in a feedback loop, the low-voltage regulator is configured to monitor a first voltage to top segments of one or more LED strings and to supply a set of controlled and variable voltages to bottom segments of the one or more LED strings without a current source, the first voltage and the set of controlled and variable voltages have opposite polarities, and voltages in the set of controlled and variable voltages are different from each other.

30. The current regulator of claim 29 , wherein the voltage regulator comprises one or more controller units each coupled to a corresponding one of the one or more LED strings, wherein each controller unit is programmed to control a current through one of the o

Assignees

• Locascio James
• Maxim Integrated Products

Inventors

• Locascio James

Classifications

• H05B45/44 Primary

  with an active control inside an LED matrix · CPC title

• Y02B20/347

  Cross-Sectional Technologies · mapped topic

• H05B33/0824

  Electricity · mapped topic

• H05B33/0818 Primary

  Electricity · mapped topic

• H05B45/38

  using boost topology · CPC title