Method and system for driving a plasma-based light source

• US 7,514,879 B2
• Filed: 11/24/2004
• Issued: 04/07/2009
• Est. Priority Date: 11/25/2003
• Status: Expired due to Fees

• Current Assignee: PureSpectrum Incorporated
• Original Assignee: PureSpectrum Incorporated
• Inventors: King, Ray, Smallwood, Robert C., Crandall, Earl F.
• Primary Examiner(s): Owens; Douglas W.
• Assistant Examiner(s): A, MINH D
• Application Number:
  US10/995,470
• Publication Number:
  US 20050134198A1
• Time in Patent Office: 1,595 Days
• Field of Search: 315/291, 315/307, 315/302, 315/246, 315/224, 315/267, 315/268, 315/272, 315/264, 315/247, 315/254, 315/274, 315/209.R
• US Class Current: 315/291
• CPC Class Codes: H05B 41/2821 by means of a single-switch converter or a parallel push-pull converter in the final stage H05B41/285 takes precedence

Abstract

A gas discharge lamp is driven with a constant current square wave from a current transformer where the number of volt-microseconds are designed such that at the start of each square wave, the voltage rises to the required ionization potential for the lamp, while the plasma has not yet started to conduct. As soon as the lamp ionizes the gas within the lamp and current flows, the voltage drops and current flows at the desired level. The current level is set to prevent the input of excessive power pulses into the lamp, to reduce the creation of infrared photons. In addition, the plasma is driven at this current level almost continuously (with reversing polarity), which does not allow the plasma time to cool down. Consequently, the lamp becomes a more efficient light emitter, thereby requiring less energy to achieve the same light output.

Claims

1. A method of driving a plasma-based light source with an electronic ballast, comprising the steps of:

applying a constant current square wave to plasma in the light source; and

maintaining a current level of the constant current square wave to obtain a temperature of the plasma that maximizes the release of light in the visible and UV light spectrums.

2. The method according to claim 1, wherein the maintaining step further comprises providing current feedback information from a switching circuit to said current source to maintain a constant current level.

3. The method according to claim 1, wherein the applying step further comprises providing sufficient ignition voltage to ionize the plasma in the plasma-based light source.

4. The method according to claim 3, wherein when the tube ionizes, the voltage drops to maintain the constant current level.

5. An electronic ballast system for driving a plasma-based light source, comprising:

a switching circuit that applies a constant current square wave to plasma in the light source; and

a current source that maintains the current level of the constant current square wave at a level to obtain a temperature of the plasma that maximizes the release of light in the visible and UV light spectrums.

6. The system according to claim 5, wherein said switching circuit comprises a push-pull circuit.

7. The system according to claim 6, wherein said switching circuit further comprises clamping circuitry.

8. The system according to claim 5, wherein said current source includes a pulse-width modulated synchronous buck converter.

9. The system according to claim 8, wherein output of said current source is fed through a choke to limit the rate of change for the current.

10. The system according to claim 8, wherein said current source further comprises a timer that shuts off current to a tube in case the tube is broken, removed, or fails to start.

11. The system according to claim 5, further including a current sensor for providing current feedback information from said switching circuit to said current source to maintain a constant current level.

12. The system according to claim 11, wherein in said current sensor further comprises a light sensor to assist in keeping the light level uniform during warm-up of the lamp and plasma and throughout the life of the lamp.

13. The system according to claim 5, further comprising a transformer for providing sufficient ignition voltage to ionize the plasma in the plasma-based light source.

14. The system according to claim 13, wherein when the tube ionizes, the voltage drops to a level which does not saturate said transformer.

15. The system of claim 5, further comprising an input conditioning circuit for conditioning the input of the AC or DC power source, wherein the input conditioning comprises at least one of transient protection, noise filtering, fusing, rectification, EMI/RFI filtering, and power factor correction.

16. An electronic ballast system for driving a plasma-based light source, comprising:

means for applying a constant current square wave to plasma in the plasma-based light source;

means for providing the sufficient ignition voltage to ionize the plasma in the plasma-based light source; and

means for maintaining a current level of the constant current square wave to obtain a temperature of the plasma that maximizes the release of light in the visible and UV light spectrums.