Magnetically shielded electrodeless light source

• US 6,433,492 B1
• Filed: 09/18/2000
• Issued: 08/13/2002
• Est. Priority Date: 09/18/2000
• Status: Expired due to Fees

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Northrop Grumman Corporation
• Inventors: Buonavita, Carl E.
• Primary Examiner(s): Philogene, Haissa
• Application Number:
  US09/663,556
• Time in Patent Office: 694 Days
• Field of Search: 315/248, 315/85, 315/344, 315/209.R, 315/291, 315/307, 315/DIG.4, 315/DIG.7, 315/278
• US Class Current: 315/248
• CPC Class Codes: H05B 41/24 in which the lamp is fed by high frequency ac, or with separate oscillator frequencyH05B41/26 takes precedence
• CPC Class Codes: Y10S 315/04 Dimming circuit for fluorescent lamps

Abstract

A dimmable electrodeless light source includes an electrodeless lamp, an electronic ballast and a dimming module. The light source further includes coupling transformers coupled to the electrodeless lamp for inductively coupling power to the lamp to generate light. An auxiliary winding electromagnetically coupled to the primary winding of at least one of the coupling transformers is driven by switching circuitry in the dimming module. The switching circuitry is pulse width modulated to control the average brightness of the light generated by the electrodeless lamp. An exemplary application for the dimmable electrodeless light source is as a backlight for a video display device, such as a liquid crystal display unit. The dimmable electrodeless light source further includes a magnetic shield device that is operably positioned with respect to the electrodeless lamp. The magnetic shield device produces a magnetic field that substantially opposes, and cancels, the magnetic field that is produced by the electrodeless lamp when energized. In an alternative embodiment, the magnetic shield device produces a magnetic field which, when combined with the lamp magnetic field, results in a total magnetic field that is substantially constant regardless of the energization level of the lamp (e.g., totally energized or dimmed). The magnetic shield thus reduces visual artifacts that might otherwise appear on a video display unit due to a variation of the magnetic field produced by the lamp.

Claims

1. A backlit display device, comprising:

an electrodeless lamp to generate light;

a power source coupled to the electrodeless lamp to energize the lamp, wherein an AC lamp current flows through the lamp when the lamp is energized, the AC lamp current producing a lamp magnetic field;

a display unit to display an image, the electrodeless lamp being operably positioned with respect to the display unit to illuminate the display unit to enhance viewing of the image; and

a shield device operably positioned with respect to the lamp and the display unit to reduce an effect of the lamp magnetic field on viewing of the image on the display unit.

2. The backlit display device as recited in claim 1, comprising:

a dimming module coupled to the electrodeless lamp, the dimming module being configured to interrupt flow of the AC lamp current to adjust brightness of the generated light.

3. The backlit display device as recited in claim 2, wherein the dimming module interrupts the flow of the AC lamp current at a repetition rate.

4. The backlit display device as recited in claim 3, comprising:

a computer; and

a video driver coupled to the computer and to the display unit to control display of the image and to refresh the image at a refresh rate,

wherein the repetition rate of the dimming module is synchronized to the refresh rate.

5. The backlit display device as recited in claim 1, wherein the shield device comprises a conductor configured in a closed loop.

6. The backlit display device as recited in claim 5, wherein the closed loop conductor is positioned between the electrodeless lamp and the display unit.

7. The backlit display device as recited in claim 1, wherein the shield device comprises a conductive coil having a plurality of turns, the coil being coupled between the power source and the electrodeless lamp.

8. The backlit display device as recited in claim 7, wherein the power source comprises a ballast.

9. The backlit display device as recited in claim 1, wherein the display unit comprises a liquid crystal display panel.

10. A method for reducing an effect of a first magnetic field on a display unit, the method comprising:

coupling energy to an electrodeless lamp to energize the electrodeless lamp, to generate light, and to generate the first magnetic field;

restricting the coupling of the energy during a dimming portion of a dimming time period to dim the generated light; and

generating a second magnetic field that substantially opposes the first magnetic field.

11. The method as recited in claim 10, wherein generating the second magnetic field comprises generating a shield current in a shield device, the shield device being operably positioned with respect to the electrodeless lamp such that the second magnetic field substantially opposes the first magnetic field.

12. The method as recited in claim 11, wherein the shield device is positioned between the electrodeless lamp and the display unit.

13. The method as recited in claim 11, wherein the shield device comprises a conductor configured as a closed loop.

14. The method as recited in claim 11, wherein the shield device comprises a conductive coil.

15. The method as recited in claim 10, wherein an AC lamp current flows in the electrodeless lamp when the lamp is energized, and wherein restricting the coupling of the energy comprises interrupting flow of the AC lamp current during the dimming portion of the dimming time period.

16. The method as recited in claim 15, comprising:

adjusting a length of the dimming portion of the dimming time period to dim the generated light over a dimming range.

17. The method as recited in claim 15, comprising:

displaying an image on the display unit;

refreshing the image on the display unit at a refresh frequency; and

synchronizing a dimming frequency of the dimming time period with the refresh frequency.

18. A method for making a magnetically shielded dimmable electrodeless light source for a backlit display device, the method comprising:

providing an electrodeless lamp having a coupling transformer to provide energy to energize the lamp;

disposing an auxiliary winding on the coupling transformer;

coupling the auxiliary winding to a drive circuit, the drive circuit being configured to establish a current carrying path through the auxiliary winding for a first time interval of a time period and to interrupt the current carrying path through the auxiliary winding for a second time interval of the time period to control brightness of light generated by the lamp; and

disposing a magnetic shield device proximate the electrodeless lamp, the magnetic shield device being disposed such that the magnetic shield device produces a shield magnetic field that substantially opposes a lamp magnetic field generated by the lamp when the lamp is energized.

19. An electrodeless light source, comprising:

an electrodeless lamp which, when energized, generates a lamp magnetic field, the electrodeless lamp operable in an operational mode comprising at least a first level of energization and a second level of energization, the second level being different than the first level; and

a shield device disposed proximate the electrodeless lamp and configured to generate a shield magnetic field, which, when combined with the lamp magnetic field, results in a substantially constant total magnetic field during the operational mode of the lamp.

20. The electrodeless light source as recited in claim 19, wherein the electrodeless lamp is substantially deenergized when at the second energization level.

21. The electrodeless light source as recited in claim 19, wherein the operational mode comprises a dimming mode in which intensity of light generated by the electrodeless lamp is reduced.

22. The electrodeless light source as recited in claim 19, comprising:

a dimming circuit coupled to the electrodeless lamp to control the level of energization of the lamp.

23. The electrodeless light source as recited in claim 22, wherein the dimming circuit is coupled to the shield device.

24. The electrodeless light source as recited in claim 23, comprising a coupling transformer inductively coupled to the electrodeless lamp, the coupling transformer coupling a power source to the lamp to energize the lamp.

25. The electrodeless light source as recited in claim 24, comprising an auxiliary winding electromagnetically coupled to the coupling transformer to couple the dimming circuit to the electrodeless lamp.

26. The electrodeless light source as recited in claim 25, wherein the shield device is coupled in series with the auxiliary winding.

27. The electrodeless light source as recited in claim 19, wherein the shield device comprises a conductive coil.

28. A method for making a magnetically shielded dimmable electrodeless light source for a backlit display device, the method comprising:

providing an electrodeless lamp having a coupling transformer to provide energy to energize the lamp;

disposing an auxiliary winding on the coupling transformer;

coupling the auxiliary winding to a drive circuit, the drive circuit being configured to establish a current carrying path through the auxiliary winding for a first portion of an operational mode and to at least partially obstruct the current carrying path through the auxiliary winding for a second portion of the operational mode to control brightness of light generated by the lamp; and

disposing a magnetic shield device proximate the electrodeless lamp, the magnetic shield device being disposed such that the magnetic shield device produces a shield magnetic field that substantially compensates for changes in a lamp magnetic field generated by the lamp during the operational mode.

29. A method for reducing an effect of a first magnetic field on a display unit, the method comprising:

energizing an electrodeless lamp at a first energization level to generate light and to generate the first magnetic field;

energizing the electrodeless lamp at a second energization level to dim the light, the second energization level causing a variation of the first magnetic field; and

generating a second magnetic field that substantially compensates for the variation of the first magnetic field.

30. The method as recited in claim 29, wherein energizing the electrodeless lamp at the second energization level comprises substantially deenergizing the lamp.

31. The method as recited in claim 29, wherein generating the second magnetic field comprises generating a shield current in a shield device, the shield device being operably positioned with respect to the electrodeless lamp such that the second magnetic field substantially compensates for the change of the first magnetic field.

32. An electrodeless light source, comprising:

an electrodeless lamp which generates a lamp magnetic field; and

a shield device disposed proximate the electrodeless lamp and configured to generate a shield magnetic field, which, when combined with the lamp magnetic field, results in a substantially constant total magnetic field.

33. The electrodeless light source as recited in claim 32, comprising:

a dimming circuit to dim light generated by the electrodeless lamp, wherein the lamp magnetic field varies when the dimming circuit dims the light.

34. The electrodeless light source as recited in claim 33, wherein the shield device is coupled to the dimming circuit.

35. An electrodeless light source, comprising:

an electrodeless lamp which generates a variable lamp magnetic field; and

a shield device disposed proximate the electrodeless lamp and configured to generate a variable shield magnetic field, the lamp magnetic field and the shield magnetic field varying opposite one another.

36. The electrodeless light source as recited in claims 35, wherein a magnitude of the shield magnetic field varies opposite a magnitude of the lamp magnetic field.

37. The electrodeless light source as recited in claim 35, wherein a direction of the shield magnetic field varies opposite a direction of the lamp magnetic field.

38. The electrodeless light source as recited in claim 35, wherein the shield magnetic field varies such that the shield magnetic field substantially opposes the lamp magnetic field.

39. The electrodeless light source as recited in claim 35, wherein the shield magnetic field varies such that, when combined with the lamp magnetic field, a substantially constant magnetic field is provided.

40. A system for compensating for an effect of a variation of a first magnetic field on a display unit, the system comprising:

means for energizing an electrodeless lamp to generate light and to generate the first magnetic field;

means for varying energization of the electrodeless lamp, thereby varying the first magnetic field; and

means for generating a variable second magnetic field to substantially compensate for the variation of the first magnetic field.

41. The system as recited in claim 40, wherein the second magnetic field varies to substantially oppose the first magnetic field such that a combined total magnetic field is substantially zero.

42. The system as recited in claim 40, wherein the second magnetic field varies such that, when combined with the first magnetic field, a combined total magnetic field is substantially constant.