Driving circuit for multiple cold cathode fluorescent lamps backlight applications

• US 7,550,928 B2
• Filed: 05/10/2006
• Issued: 06/23/2009
• Est. Priority Date: 04/15/2003
• Status: Expired due to Fees

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: Liu, Da
• Primary Examiner(s): VU, DAVID HUNG
• Application Number:
  US11/432,784
• Publication Number:
  US 20060202635A1
• Time in Patent Office: 1,140 Days
• Field of Search: 315/274, 315/275, 315/276, 315/277, 315/278, 315/279, 315/281, 315/282, 315/224, 315/312
• US Class Current: 315/276
• CPC Class Codes: H05B 41/282 with semiconductor devices H05B41/2806, H05B41/288, H05B41/295 take precedence
• CPC Class Codes: H05B 41/2827 using specially adapted components in the load circuit, e.g. feed-back transformers, piezoelectric transformers; using specially adapted load circuit configurations
• CPC Class Codes: H05B 41/2828 using control circuits for the switching elements H05B41/2827 takes precedence
• CPC Class Codes: H05B 41/3921 with possibility of light intensity variations
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

Abstract

The present invention provides a driving circuit for driving a light source. The driving circuit includes a serial-arranged transformers system having multiple primary windings and secondary windings; a first switch conducting current though a first path and a second switch conducting current though a second path. The first path is a first set of primary windings connected in series and the second path is a second set of primary windings connected in series and the first set of primary transformer windings and the second set of primary transformer windings form the dual primary windings of the transformers respectively. Based on the conduction of each switch, a DC voltage source supplies power to the primary windings of the transformers, which in turn powers on the light source connected to the secondary windings of the transformers.

Claims

1. A driving circuit for driving a light source comprising:

a transformer comprising a plurality of primary windings and a plurality of secondary windings, wherein said plurality of primary windings are coupled to a power source and comprise a first set of primary windings coupled in series and a second set of primary windings coupled in series, and wherein said light source is coupled between a positive polarity of a first secondary winding and a negative polarity of a second secondary winding;

a first switch for conducting current through a first path comprising said first set of primary windings;

a second switch for conducting current through a second path comprising said second set of primary windings, wherein said first switch and said second switch are enabled alternately to drive said light source; and

feedback circuitry coupled to a negative polarity of said first secondary winding and to a positive polarity of said second secondary winding, said feedback circuitry providing signals indicating conditions at said light source and useful for adjusting said power source accordingly.

2. The driving circuit as claimed in claim 1, wherein said driving circuit comprises a plurality of transformers.

3. The driving circuit as claimed in claim 1, wherein said primary windings comprise dual primary windings.

4. The driving circuit as claimed in claim 3, wherein said dual primary windings are wound on multiple cores.

5. The driving circuit as claimed in claim 3, wherein said dual primary windings are wound on a single core.

6. The driving circuit as claimed in claim 4, wherein said secondary windings are wound on said multiple cores.

7. The driving circuit as claimed in claim 5, wherein said secondary windings are wound on a single core.

8. The driving circuit as claimed in claim 1 further comprises a pulse-width modulation generator configured to generate a first pulse-width modulation signal and a second pulse-width modulation signal to said first switch and second switch respectively.

9. The driving circuit as claimed in claim 3, wherein said dual primary winding is coupled to said first switch and said second switch.

10. The driving circuit as claimed in claim 1, wherein the winding ratio of said transformer ranges from 10 to 100.

11. The driving circuit as claimed in claim 1, wherein said first switch is selected from a transistor group comprising metal oxide semiconductor field effect transistor, bipolar junction transistor, and insulated gate bipolar junction transistor.

12. The driving circuit as claimed in claim 1, wherein said second switch is selected from a transistor group comprising of metal oxide semiconductor field effect transistor, bipolar junction transistor, and insulated gate bipolar junction transistor.

13. A method for driving a light source, said method comprising:

switching a first switch to conduct current through a first path comprising a first set of primary windings coupled in series in a transformer;

switching a second switch to conduct current through a second path comprising a second set of primary windings coupled in series in said transformer, wherein said first set of primary windings and said second set of primary windings comprise a plurality of primary windings corresponding to said transformer, wherein said light source is coupled between a positive polarity of a first secondary winding of said transformer and a negative polarity of a second secondary winding of said transformer, and wherein feedback circuitry is coupled to a negative polarity of said first secondary winding and to a positive polarity of said second secondary winding, said feedback circuitry providing signals indicating conditions at said light source; and

adjusting said power source according to said signals.

14. The driving circuit as claimed in claim 13, wherein said first set of primary windings and said second set of primary windings comprise said plurality of primary windings corresponding to a plurality of transformers having a plurality of secondary windings coupled to said light source.

15. The method as claimed in claim 14, wherein said plurality of primary windings comprise dual primary windings.

16. The method as claimed in claim 13 further comprises the step of selectively switching said first switch and said second switch alternately.

17. The method as claimed in claim 16, wherein said current flows through said first path to said first switch if said first switch is turned on.

18. The method as claimed in claim 16, wherein said current flows through said second path to said second switch if said second switch is turned on.

19. The method as claimed in claim 15, wherein said dual primary windings are on multiple cores respectively.

20. The method as claimed in claim 15, wherein said dual primary windings are on a single core.

21. The method as claimed in claim 19, wherein said secondary windings are on said multiple cores respectively.

22. The method as claimed in claim 20, said secondary windings are on said single core.

23. The method as claimed in claim 13 further comprising the step of using a first pulse-width modulation signal and a second pulse-width modulation signal to switch said first switch and second switch respectively.

24. The method as claimed in claim 13, wherein said first switch is selected from the transistor group comprising of metal oxide semiconductor field effect transistor, bipolar junction transistor, and insulated gate bipolar junction transistor.

25. The method as claimed in claim 13, wherein said second switch is selected from the transistor group comprising of metal oxide semiconductor field effect transistor, bipolar junction transistor, and insulated gate bipolar junction transistor.

26. A display system, comprising:

a plurality of light sources; and

a driving circuit for driving said plurality of light sources, said driving circuit comprising;

a transformer comprising a plurality of primary windings and a plurality of secondary windings, wherein said plurality of primary windings are coupled to a power source and comprise a first set of primary windings coupled in series and a second set of primary windings coupled in series, and wherein said plurality of secondary windings comprise a first secondary winding and a second secondary winding that are coupled to a light source of said light sources, said light source coupled between a positive polarity of said first secondary winding and a negative polarity of said second secondary winding;

a first switch for conducting current through a first path comprising said first set of primary windings;

a second switch for conducting current through a second path comprising said second set of primary windings, wherein said first switch and said second switch are enabled alternately to drive said light sources; and

first feedback circuitry coupled to a negative polarity of said first secondary winding and second feedback circuitry coupled to a positive polarity of said second secondary winding, said first and second feedback circuitry providing signals indicating conditions at said light source, wherein said power source is adjusted according to said conditions.

27. The display system as claimed in claim 26, wherein said driving circuit comprises a plurality of transformers.

28. The display system as claimed in claim 26, wherein said primary windings comprise dual primary windings.

29. The display system as claimed in claim 28, wherein said dual primary windings are on multiple cores respectively.

30. The display system as claimed in claim 28, wherein said dual primary windings are on a single core.

31. The display system as claimed in claim 29, wherein said secondary windings are on said multiple cores respectively.

32. The display system as claimed in claim 30, wherein said secondary windings are on said single core.

33. The display system as claimed in claim 26, said driving circuit further comprises a pulse-width modulation generator configured to generate a first pulse-width modulation signal and a second pulse-width modulation signal to said first switch and second switch respectively.

34. The display system as claimed in claim 28, wherein said dual primary winding is coupled to said first switch and said second switch.

35. The display system as claimed in claim 26, wherein the winding ratio of said transformer ranges from 10 to 100.