Power supply for an LCD display

• US 8,179,053 B2
• Filed: 09/12/2008
• Issued: 05/15/2012
• 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: Lin, Yung-Lin, Liu, Da
• Primary Examiner(s): Owens, Douglas W
• Assistant Examiner(s): A, Minh D
• Application Number:
  US12/209,842
• Publication Number:
  US 20090039796A1
• Time in Patent Office: 1,341 Days
• Field of Search: 315/276, 315/277, 315/278, 315/291, 315/307, 315/219, 315/312, 315/185.R, 315/185.S
• US Class Current: 315/224
• 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

A power supply system is provided for a multiple lamp LCD panel. In one aspect, the power supply includes a plurality of transformers for driving a plurality of respective CCFLs. The primary sides of each transformer are coupled in series to thereby reduce the stress on each transformer. For LCD panels that include longer CCFLs, a power supply is provided that includes a plurality of transformers for driving a plurality of respective CCFLs. The primary sides of each transformer are coupled in series and each lamp is coupled to two secondary sides of the transformers, thereby reducing the problems associated with longer CCFL tubes. In any of the embodiments, the power supply can be adapted to convert a high voltage DC signal to high voltage AC used to power the lamps.

Claims

1. A DC/AC inverter circuit, comprising:

a transformer comprising a primary winding for receiving an AC signal, and comprising a first secondary winding and a second secondary winding;

a first cold cathode florescent lamp (CCFL) coupled to said first secondary winding and said second secondary winding in series, said first CCFL comprising a first end coupled to a positive polarity terminal of said first secondary winding and a second end coupled to a negative polarity terminal of said second secondary winding,

wherein said first end of said first CCFL is coupled to ground through said positive polarity terminal of said first secondary winding and a negative polarity terminal of said first secondary winding, and wherein said second end of said first CCFL is coupled to ground through said negative polarity terminal of said second secondary winding and a positive polarity terminal of said second secondary winding.

2. The DC/AC inverter circuit as claimed in claim 1, further comprising:

a current feedback circuit coupled in series with said first CCFL, said first secondary winding and second secondary winding, and operable for providing a current feedback signal to said inverter controller indicative of a current flowing through said first CCFL.

3. The DC/AC inverter circuit as claimed in claim 2, wherein said inverter controller adjusts said current flowing through said first CCFL according to said current feedback signal.

4. The DC/AC inverter circuit as claimed in claim 1, wherein said current feedback circuit comprises:

a first current sensor coupled to said first secondary winding and operable for providing a first current sensing signal indicative of a current flowing through said first secondary winding; and

a second current sensor coupled to said second secondary winding and operable for providing a second current sensing signal indicative of a current flowing through said second secondary winding.

5. The DC/AC inverter circuit as claimed in claim 4, wherein said current feedback signal is generated according to said first current sensing signal and said second current sensing signal.

6. The DC/AC inverter circuit as claimed in claim 4, wherein said first current sensor is coupled to a negative polarity terminal of said first secondary winding, and wherein said second current sensor is coupled to a positive polarity terminal of said second secondary winding.

7. The DC/AC inverter circuit as claimed in claim 1, wherein an output AC signal at said positive polarity terminal of said first secondary winding is approximately 180 degree out of phase with respect to an output AC signal at said negative polarity terminal of said second secondary winding.

8. The DC/AC inverter circuit as claimed in claim 1, further comprising:

an inverter controller coupled to a power train and operable for converting a DC signal to said AC signal.

9. The DC/AC inverter circuit as claimed in claim 8, wherein said inverter controller adjusts said voltage across said first CCFL according to said voltage feedback signal.

10. The DC/AC inverter circuit as claimed in claim 1, further comprising:

a second CCFL coupled to said first secondary winding and said second secondary winding in series, said second CCFL comprising a first end coupled to said negative polarity terminal of said second secondary winding and a second end coupled to said positive polarity terminal of said first secondary winding; and

a capacitor divider feedback circuit electrically coupled between said first CCFL and said second CCFL at a point between said first end of said first CCFL and said positive polarity terminal of said first secondary winding and also at a point between said first end of said second CCFL and said negative polarity terminal of said second secondary winding, said capacitor divider feedback circuit operable for providing a voltage feedback signal to an inverter controller, said voltage feedback signal generated using voltage feedback information taken from both said first and second CCFLs.

11. The DC/AC inverter circuit as claimed in claim 10, wherein said capacitor divider feedback circuit comprises:

a first capacitor divider electrically coupled to said first secondary winding and operable for providing a first voltage sensing signal indicative of a voltage across said first secondary winding; and

a second capacitor divider electrically coupled to said second secondary winding and operable for providing a second voltage sensing signal indicative of a voltage across said second secondary winding.

12. The DC/AC inverter circuit as claimed in claim 11, wherein said voltage feedback signal is generated according to said first voltage sensing signal and said second voltage sensing signal.

13. The DC/AC inverter circuit as claimed in claim 11, wherein said first capacitor divider is coupled between said positive polarity terminal of said first secondary winding and ground, and wherein said second capacitor divider is coupled between said negative polarity terminal of said second secondary winding and ground.

14. A display system, comprising:

a display panel;

an inverter controller coupled to a power train and operable for converting a DC signal to an AC signal;

a transformer coupled to said power train and comprising a first primary winding and a second primary winding coupled in series and operable for receiving said AC signal, and comprising a first secondary winding and a second secondary winding;

a cold cathode florescent lamp (CCFL) coupled to said first secondary winding and said second secondary winding in series and operable for illuminating said display panel, said CCFL comprising a first end coupled to a positive polarity terminal of said first secondary winding and a second end coupled to a negative polarity terminal of said second secondary winding;

a current feedback circuit coupled in series with said CCFL, said first secondary winding and second secondary winding, and operable for providing a current feedback signal to said inverter controller indicative of a current flowing through said CCFL; and

a capacitor divider feedback circuit coupled to said CCFL and operable for providing a voltage feedback signal to said inverter controller indicative of a voltage across said CCFL,

wherein said first end of said CCFL is coupled to ground through said positive polarity terminal of said first secondary winding and a negative polarity terminal of said first secondary winding, and wherein said second end of said CCFL is coupled to ground through said negative polarity terminal of said second secondary winding and a positive polarity terminal of said second secondary winding.

15. The display system as claimed in claim 14, wherein said capacitor divider feedback circuit comprises:

a first capacitor divider coupled to said first secondary winding and operable for providing a first voltage sensing signal indicative of a voltage across said first secondary winding; and

a second capacitor divider coupled to said second secondary winding and operable for providing a second voltage sensing signal indicative of a voltage across said second secondary winding.

16. The display system as claimed in claim 15, wherein said voltage feedback signal is generated according to said first voltage sensing signal and said second voltage sensing signal.

17. The display system as claimed in claim 15, wherein said first capacitor divider is coupled between said positive polarity terminal of said first secondary winding and ground, and wherein said second capacitor divider is coupled between said negative polarity terminal of said second secondary winding and ground.

18. The display system as claimed in claim 14, wherein said current feedback circuit comprises:

a first current sensor coupled to said first secondary winding and operable for providing a first current sensing signal indicative of a current flowing through said first secondary winding; and

a second current sensor coupled to said second secondary winding and operable for providing a second current sensing signal indicative of a current flowing through said second secondary winding.

19. The display system as claimed in claim 18, wherein said current feedback signal is generated according to said first current sensing signal and said second current sensing signal.

20. The display system as claimed in claim 18, wherein said first current sensor is coupled to a negative polarity terminal of said first secondary winding, and wherein said second current sensor is coupled to a positive polarity terminal of said second secondary winding.

21. The display system as claimed in claim 14, wherein an output AC signal at said positive polarity terminal of said first secondary winding is approximately 180 degree out of phase with respect to an output AC signal at said negative polarity terminal of said second secondary winding.

22. The display system as claimed in claim 14, wherein said inverter controller adjusts said current flowing through said CCFL according to said current feedback signal.

23. The display system as claimed in claim 14, wherein said inverter controller adjusts said voltage across said CCFL according to said voltage feedback signal.

24. A method for providing power to a cold cathode fluorescent lamp (CCFL) of a display system, said method comprising:

receiving an AC signal by a primary winding of a transformer;

generating a first output AC signal at a positive polarity terminal of a first secondary winding of said transformer;

generating a second output AC signal at a negative polarity terminal of a second secondary winding of said transformer;

powering a first terminal of said CCFL by said first output AC voltage and powering a second terminal of said CCFL by said second output AC voltage, wherein said CCFL is coupled to said first secondary winding and said second secondary winding in series and is coupled between said positive polarity terminal of said first secondary winding and said negative polarity terminal of said second secondary winding, wherein the center of said CCFL is positioned at zero potential;

receiving a voltage feedback signal from a capacitor divider feedback circuit indicative of a voltage across said CCFL; and

controlling power of said CCFL according to said voltage feedback signal.

25. The method as claimed in claim 24, further comprising:

receiving a current feedback signal indicative of a current flowing through said CCFL; and

controlling power of said CCFL according to said current feedback signal.

26. The method as claimed in claim 24, wherein said first output AC signal is approximately 180 degree out of phase with respect to said second output AC signal.

27. The method as claimed in claim 24, further comprising:

providing a first current sensing signal indicative of a current flowing through said first secondary winding by a first current sensor coupled to said first secondary winding;

providing a second current sensing signal indicative of a current flowing through said second secondary winding by a second current sensor coupled to said second secondary winding; and

generating said current feedback signal according to said first current sensing signal and said second current sensing signal.

28. The method as claimed in claim 24, further comprising:

providing a first voltage sensing signal indicative of a voltage across said first secondary winding by a first capacitor divider electrically coupled to said first secondary winding;

providing a second voltage sensing signal indicative of a voltage across said second secondary winding by a second capacitor divider electrically coupled to said second secondary winding; and

generating said voltage feedback signal according to said first voltage sensing signal and said second voltage sensing signal.