Compact fluorescent lamp dimming system

• US 5,144,205 A
• Filed: 12/12/1989
• Issued: 09/01/1992
• Est. Priority Date: 05/18/1989
• Status: Expired due to Fees

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Lutron Electronics Company Incorporated (Lutron Electronics)
• Inventors: Jurell, Scott R., Motto, Eric R.
• Primary Examiner(s): LaRoche, Eugene R.
• Assistant Examiner(s): DINH, SON T
• Application Number:
  US07/450,185
• Time in Patent Office: 994 Days
• Field of Search: 315/244, 315/210, 315/119, 315/199, 315/172, 315/174, 315/176, 315/DIG. 7, 315/224, 315/DIG. 2, 315/258
• US Class Current: 315/244
• CPC Class Codes: H05B 41/382 during the transitional start-up phase
• CPC Class Codes: H05B 41/3924 by phase control, e.g. using a triac H05B41/3922 takes precedence
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
• CPC Class Codes: Y10S 315/02 High frequency starting operation for fluorescent lamp
• CPC Class Codes: Y10S 315/07 Starting and control circuits for gas discharge lamp using transistors

Abstract

A dimming system provides power from a switch-controlled power source in series with a leakage auto-transformer to a compact fluorescent lamp. The system incorporates a high-frequency resonant converter that provides high voltages to strike and maintain an electric discharge in the lamp. The converter is loaded in parallel by the lamp, whose impedance damps the converter to stabilize lamp operation. An inductor, connected between the leakage auto-transformer and the resonant converter, isolates the switch-controlled power source from the high-frequency voltage. The system can be used with a variety of standard leakage reactance auto-transformers to provide full-range dimming of compact fluorescent lamps from 5 to 100 percent light output with minimal flicker.

Claims

1. A control system for providing electrical power from a source to a gas discharge lamp, comprising:

a) a resonant circuit having input and output terminals, said lamp being connectable across said output terminals to provide parallel loading of said resonant circuit; and

b) driving means to provide a symmetrical high-frequency ac driving voltage across said input terminals to achieve a resonant response in said resonant circuit and produce a voltage across said output terminals sufficient to strike and maintain an electric discharge in said lamp, said driving means comprising an oscillating circuit including a switching transistor controlled by a regenerative base-drive transformer wherein said driving means after striking said electric discharge drives said resonant circuit at a frequency away from a peak response frequency of said resonant circuit.

2. The control system of claim 1 wherein said resonant circuit comprises a capacitor and an inductor connected in series.

3. The control system of claim 2 wherein said lamp is connectable across said capacitor.

4. The control system of claim 1 wherein said oscillating circuit includes two switching transistors, connected in series, and a regenerative base-drive transformer to alternately provide base drive to each of said switching transistors.

5. The control system of claim 1, wherein the frequency away from said peak response frequency of said driving voltage is about 37 kHz and said peak response frequency of said resonant circuit is about 40 kHz.

6. The control system of claim 1 wherein the voltage across said output terminals is approximately between 100 V and 1000 V.

7. A control system for providing electrical power from a source to a gas discharge lamp, comprising:

a) a ballast connected between said source and said lamp to provide a first current at a first frequency from said source to said lamp, substantially determining the power thereto;

b) means connected between said source and said lamp, said means having a resonant circuit connected in parallel with said lamp to simultaneously and continuously provide a second current at a second frequency, higher than said first frequency and corresponding to the peak response frequency of said resonant circuit, from said source to said lamp to strike and maintain an electric discharge therein; and

c) a first inductor connected between said lamp and said ballast to substantially block said second current from propagating through said ballast.

8. The control system of claim 7, wherein said ballast comprises a leakage reactance auto-transformer.

9. The control of claim 7 wherein said resonant circuit comprises a capacitor and a second inductor connected in series.

10. The control system of claim 7 wherein said second frequency is approximately between 20 kHz and 50 kHz.

11. The control system of claim 7 wherein said inductor has an inductance approximately between 20 mH and 100 mH.

12. A control system for providing electrical power from a source to a gas discharge lamp, comprising:

a) a resonant circuit having input and output terminals, said lamp connectable across said output terminals to provide parallel loading of said resonant circuit;

b) driving means for providing a high-frequency driving voltage across said input terminals to acheive a resonant response, having a predetermined peak voltage value, in said reasonant circuit and produce a voltage on said output terminals sufficient to strike and maintain an electric discharge in said lamp;

c) means connected to said resonant circuit for sensing when said resonant response exceeds said predetermined peak voltage value; and

d) means connected to said driving means and responsive to said sensing means for shifting the frequency of said driving voltage away from the peak response frequency of said resonant circuit when said resonant response exceeds said predetemined peak voltage value;

whereby the voltage across said output terminals remains below a predetermined maximum value.

13. The control system of claim 12 wherein said resonant circuit comprises a capacitor and an inductor connected in series.

14. The control system of claim 13 wherein said lamp is connectable across said capacitor.

15. The control system of claim 12 wherein said driving means comprises an oscillating circuit including a switching transistor controlled by a regenerative base-drive transformer.

16. The control system of claim 12 wherein the frequency of said driving voltage is approximately between 20 kHz and 50 kHz.

17. The control system of claim 12 wherein said said sensing means comprises a resistor in series with said resonant circuit and a transistor having its base connected to a first terminal of said resistor and its emitter connected to a second terminal of said resistor.

18. The control system of claim 17 wherein said driving means comprises a regenerative base-drive transformer and said frequency shifting means comprises a secondary winding of said transformer connected in series with said transistor to load said driving means when said transistor is conductive.

19. A control system for providing electrical powers from a source to two gas discharge lamps, comprising:

a) a pair of ballasts, each connected between said source and a corresponding one of said lamps, to provide a first current at a first frequency from said source to said lamps in parallel, substantially determining the power thereto;

b) a resonant circuit connected between said source and said lamps to simultaneously and continuously provide a second current at a second frequency, higher than said first frequency, from said source to said lamps in series to strike and maintain an electric discharge therein;

c) driving means to provide a driving voltage across said resonant circuit sufficient to achieve a resonant response therein; and

d) first and second inductors, each connected between one of said lamps and said corresponding ballast, to substantially block said second current from propagating through said ballasts.

20. The control system of claim 19 wherein said ballasts comprise leakage reactance auto-transformers.

21. The control system of claim 19 wherein said resonant circuit comprises a capacitor and a third inductor connected in series.

22. The control system of claim 21 wherein said lamps are connectable in series across said capacitor.

23. The control system of claim 19 wherein said driving means comprises an oscillating circuit including a switching transistor controlled by a regenerative base-drive transformer.

24. The control system of claim 19 wherein said second frequency is approximately between 20 kHz and 50 kHz.

25. The control system of claim 19 wherein said first and second inductors each have an inductance approximately between 20 mH and 100 mH.

26. The control system of claim 19 further comprising a capacitor connected between said first and second inductors.