Fluorescent lamp dimming adaptor kit

• US 4,682,083 A
• Filed: 07/11/1986
• Issued: 07/21/1987
• Est. Priority Date: 10/29/1984
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Alley, Robert P.
• Primary Examiner(s): Boudreau, Leo H.
• Assistant Examiner(s): Razavi, Michael
• Application Number:
  US06/883,469
• Time in Patent Office: 375 Days
• Field of Search: 315/307, 315/291, 315/297, 315/287, 315/DIG. 4, 315/194, 315/311, 315/308, 315/208
• US Class Current: 315/307
• CPC Class Codes: H05B 41/3927 by pulse width modulation H05B41/3922 takes precedence
• CPC Class Codes: Y10S 315/04 Dimming circuit for fluorescent lamps

Abstract

A conventional non-dimming ballast for fluorescent lamps is modified to achieve a 100:1 dimming ratio by connecting a switching module to the ballast. The switching module switches current to and from the fluorescent lamps under control of a level control, resulting in the desired light output. The switching module may be connected either in series or in parallel with the lamps.

Claims

1. An add-on fluorescent lamp dimming adaptor for connecting to a conventional nondimming ballast in a fluorescent lighting system, said system including a source of ac voltage, said ballast having terminals for connecting to a fluorescent lamp, said adaptor comprising:

a switching module adapted to be coupled to said terminals for switching current from said lamp, said switching module being connected in parallel with said lamp so as to divert current from said lamp when said switching module conducts; and

a level control coupled to said switching module, said level control controlling the conductive state of said switching module to vary the current in said lamp according to a dimming control signal supplied to said level control, said level control causing said switching module to switch at a frequency in the range of 300 hertz and higher during times that said lamp current is being varied.

2. The fluorescent lamp dimming adaptor recited in claim 1 wherein said switching module comprises a gate controlled semiconductor switch and a diode bridge rectifier, said semiconductor switch being coupled to the output of said diode rectifier.

3. The fluorescent lamp dimming adaptor of claim 1 wherein said level control is adapted to be coupled to said ac source voltage and is synchronized to the zero crossings of said ac source voltage.

4. The fluorescent lamp dimming adaptor recited in claim 1 wherein said level control comprises:

a zero crossing detector connected to said ac source;

a PWM generator for generating a pulse train which is pulse width modulated according to said dimming control signal, said PWM generator being reset by said zero crossing detector at each zero crossing of said ac source voltage; and

a light emitting diode connected to the output of said PWM generator for optocoupling to said switching module.

5. The fluorescent lamp dimming adaptor recited in claim 4 wherein said switching module comprises a gate controlled semiconductor switch, a diode bridge rectifier and a gate circuit, said semiconductor switch being coupled to the output of said diode rectifier, said gate circuit being photo-coupled to said light emitting diode.

6. The fluorescent lamp dimming adaptor recited in claim 5 wherein said gate controlled semiconductor switch comprises an IGT.

7. The fluorescent lamp dimming adaptor recited in claim 1 wherein said level control comprises:

circuit means for providing high frequency switching signals for a variable portion of each half wave of the voltage in the primary circuit of said ballast according to said dimming control signal; and

a light emitting diode connected to the output of said circuit means for optocoupling to said switching module.

8. The fluorescent lamp dimming adaptor recited in claim 7 wherein said switching module comprises a gate controlled semiconductor switch, a diode bridge rectifier and a gate circuit, said semiconductor switch being coupled to the output of said diode rectifier, and said gate circuit being photo-coupled to said light emitting diode.

9. The fluorescent lamp dimming adaptor recited in claim 8 wherein said gate controlled semiconductor switch comprises an IGT.

10. The fluorescent lamp dimming adaptor recited in claim 1 wherein said level control comprises:

a sawtooth oscillator coupled to said ac source; and

a comparator having one input coupled to the output of said oscillator and a second input responsive to said dimming control signal, the output of said comparator being coupled to said switching module.

11. The fluorescent lamp dimming adaptor recited in claim 10 wherein said sawtooth oscillator operates at a frequency in the range of 3000 hertz and higher.

12. An add-on fluorescent lamp dimming adaptor for connecting to a conventional rapid-start ballast in a fluorescent lighting system, said fluorescent lighting system including a source of ac voltage, said ballast having terminals for connecting to two series-coupled fluorescent lamps, said adapter comprising:

a switching module adapted to be coupled to said terminals for switching current from said lamps, said switching module being connected in parallel with said lamps; and

a level control coupled to said switching module, said level control controlling the conductive state of said switching module to vary the current in said lamps according to a dimming control signal supplied to said level control, said level control causing said switching module to switch at a frequency in the range of 300 hertz and higher during times when the current in said lamps is being varied.

13. The fluorescent lamp dimming adaptor recited in claim 12 wherein said switching module comprises a gate controlled semiconductor switch and a diode bridge rectifier, said semiconductor switch being coupled to the output of said diode rectifier.

14. An add-on fluorescent lamp dimming adaptor for connecting to a conventional nondimming ballast in a fluorescent lighting system, said system including a source of ac voltage, said ballast having terminals for connecting to a fluorescent lamp, said adaptor comprising:

a switching module adapted to be coupled in series with said terminals and said lamp for switching current through said lamp, said switching module thus conducting current to said lamp when said module is conductive and interrupting current to said lamp when said module is nonconductive; and

a level control coupled to said switching module, said level control controlling the conductive state of said switching module to vary the current in said lamp according to a dimming control signal supplied to said level control, said level control causing said switching module to switch at a frequency in the range of 300 hertz and higher during times when said lamp current is being varied.

15. The fluorescent lamp dimming adaptor of claim 14 wherein said switching module comprises a gate controlled semiconductor switch and a diode bridge rectifier, said semiconductor switch being coupled to the output of said diode rectifier.

16. The fluorescent lamp dimming adaptor of claim 14 wherein said level control is adapted to be coupled to said ac source voltage and is synchronized to the zero crossings of said ac source voltage.

17. The fluorescent lamp dimming adaptor of claim 14 wherein said level control comprises:

a zero crossing detector connected to said ac source;

a PWM generator for generating a pulse train which is pulse width modulated according to said dimming control signal, said PWM generator being reset by said zero crossing detector at each zero crossing of said ac source voltage; and

a light emitting diode connected to the output of said PWM generator for optocoupling to said switching module.

18. The fluorescent lamp dimming adaptor of claim 17 wherein said switching module comprises a gate controlled semiconductor switch, a diode bridge rectifier and a gate circuit, said semiconductor switch being coupled to the output of said diode rectifier, said gate circuit being photo-coupled to said light emitting diode.

19. The fluorescent lamp dimming adaptor of claim 18 wherein said gate controlled semiconductor switch comprises an IGT.

20. The fluorescent lamp dimming adaptor of claim 14 wherein said level control comprises:

circuit means for providing high frequency switching signals for a variable portion of each half wave of the voltage in the primary circuit of said ballast according to said dimming control signal; and

a light emitting diode connected to the output of said circuit means for optocoupling to said switching module.

21. The fluorescent lamp dimming adaptor of claim 20 wherein said switching module comprises a gate controlled semiconductor switch, a diode bridge rectifier and a gate circuit, said semiconductor switch being coupled to the output of said diode rectifier, and said gate circuit being photo-coupled to said light emitting diode.

22. The fluorescent lamp dimming adaptor of claim 21 wherein said gate controlled semiconductor switch comprises an IGT.

23. The fluorescent lamp dimming adaptor of claim 14 wherein said level control comprises:

a sawtooth oscillator coupled to said ac source; and

a comparator having one input coupled to the output of said oscillator and a second input responsive to said dimming control signal, the output of said comparator being coupled to said switching module.

24. The fluorescent lamp dimming adaptor of claim 23 wherein said sawtooth oscillator operates at a frequency in the range of 3,000 hertz and higher.

25. An add-on fluorescent lamp dimming adaptor for connecting to a conventional rapid-start ballast in a fluorescent lighting system, said fluorescent lighting system including a source of ac voltage, said ballast having terminals for connecting to two fluorescent lamps, and a transformer coupled between said lamps, said adaptor comprising:

a switching module adpated to be coupled to said terminals for switching current from said lamps, said switching module being coupled in series with said lamps and briding said transformer; and

a level control coupled to said switching module, said level control controlling the conductive state of said switching module to vary the current in said lamps according to a dimming control signal supplied to said level control, said level control causing said switching module to switch at a frequency in the range of 300 hertz and higher during times when the current in said lamps is being varied.

26. The fluorescent lamp dimming adaptor recited in claim 25 wherein said switching module comprises a gate controlled semiconductor switch and a diode bridge rectifier, said semiconductor switch being coupled to the output of said diode rectifier.