Driving circuit for multiple cold cathode fluorescent lamps backlight applications

• US 7,075,245 B2
• Filed: 07/22/2004
• Issued: 07/11/2006
• Est. Priority Date: 04/15/2003
• Status: Expired due to Fees

• Current Assignee: O2Micro International Limited
• Original Assignee: O2 Micro Incorporated
• Inventors: Liu, Da
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): Lie, Angela M
• Application Number:
  US10/898,421
• Publication Number:
  US 20040263092A1
• Time in Patent Office: 719 Days
• Field of Search: 315/244, 315/276, 315/247, 315/209.R, 315/291, 315/277
• US Class Current: 315/219
• 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 multiple primary windings and a secondary winding, wherein said multiple primary windings are coupled to a power source and said secondary winding is coupled to said light source;

a first switch for conducting current through a first path comprising a first set of primary windings coupled in series;

a second switch for conducting current through a second path comprising a second set of primary windings coupled in series, wherein said first set of primary windings and said second set of primary windings comprise said multiple primary windings corresponding to said transformer; and

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, wherein said first pulse-width modulation signal has a 180 degree phase shift to said second pulse-width modulation signal.

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 2, wherein said plurality of transformers comprise a plurality of secondary windings.

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

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

6. The driving circuit as claimed in claim 4, wherein said dual primary windings are wound on a single core.

7. The driving circuit as claimed in claim 5, wherein said secondary windings are wound on said multiple cores.

8. The driving circuit as claimed in claim 6, wherein said secondary windings are wound on a single core.

9. The driving circuit as claimed in claim 4, 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 multiple primary windings corresponding to said transformer; and

using a first pulse-width modulation signal and a second pulse-width modulation signal to switch said first switch and second switch respectively, wherein said first pulse-width modulation signal has a 180 degree phase shift to said second pulse-width modulation signal.

14. The driving circuit as claimed in claim 13, wherein said first set of primary windings and said second set of primary windings comprise multiple 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 multiple 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, 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.

24. 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.

25. 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 multiple primary windings and a secondary winding;

a first switch for conducting current through a first path comprising a first set of primary windings coupled in series;

a second switch for conducting current through a second path comprising a second set of primary windings coupled in series, wherein said first set of primary windings and said second set of primary windings comprise said multiple primary windings corresponding to said transformer; and

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, wherein said first pulse-width modulation signal has a 180 degree phase shift to said second pulse-width modulation signal.

26. The display system as claimed in claim 25, wherein said driving circuit comprises a plurality of transformers.

27. The display system as claimed in claim 26, wherein said plurality of transformers comprise a plurality of secondary windings.

28. The display system as claimed in claim 27, wherein said multiple 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 28, wherein said dual primary winding is coupled to said first switch and said second switch.

34. The display system as claimed in claim 25, wherein the winding ratio of said transformer ranges from 10 to 100.