Claims
- 1. In combination,
- at least one fluorescent lamp;
- a DC voltage supply where said DC voltage corresponds to the difference between a first voltage level and a second voltage level;
- converter means including (a) a resonant circuit for converting said DC voltage to a sinusoidal current (b) a pair of controllable switches connected between said first and second voltage levels, (c) control means for alternately generating a pair of control pulse trains for alternately switching said switches on and off where the pulse repetition frequencies of the pulse control trains are the same to thus switch said first and second voltage levels to said fluorescent lamp at the pulse repetition frequency of said pulse control trains under the control of the resonant circuit so that said lamp is excited by said sinusoidal current, and (d) means for varying the duty cycles of said pulse control trains to thus effect dimming of the lamp light intensity; and where the frequency of the sinusoidal current remains the same as that of the resonant circuit both for the initial excitation of the lamp and for the continued operation of the lamp subsequent to the initial excitation.
- 2. The combination as in claim 1 where said load means includes a transformer for transformer coupling the resonant circuit to the lamp.
- 3. The combination as in claim 1 where said lamp is in series circuit with said resonant circuit.
- 4. A combination as in claim 1 including a plurality of fluorescent lamps, all of which are connected in parallel.
- 5. The combination of claim 1 where said convertor means includes means for dimming the light intensity of the lamp.
- 6. The combination of claim 5 including means for remotely controlling the dimming means.
- 7. The combination of claim 1 including means for supplying constant voltage to the fluorescent tube filaments.
- 8. The combination of claim 1 where said convertor means includes means for regulating line voltage.
- 9. The combination of claim 1 where said convertor means includes means for substantially eliminating AC buzz and flickering of the fluorescent lamp.
- 10. The combination as in claim 1, where said resonant circuit is a series resonant circuit and said load means are connected in series with the series resonant circuit.
- 11. The combination as in claim 10 where said series resonant circuit includes an inductor and a capacitor.
- 12. The combination as in claim 11 where said inductor and said capacitor are disposed on opposite sides of the load means.
- 13. The combination as in claim 11 where said inductor and said capacitor are disposed on opposite sides of the load means.
- 14. The combination as in claim 10 where said series resonant circuit and said lamp are connected in series resonant circuit.
- 15. The combination as in claim 10 including a transformer for transformer coupling said series resonant circuit to said lamp.
- 16. The combination of claim 10, where said controllable switches are connected in series between said first and second voltage levels and the circuit including said series resonant circuit and said load means is connected to a point intermediate the first and second controllable switches.
- 17. The combination as in claim 10 including means for rendering the pulse repetition frequency of the control pulse trains substantially equal to the resonant frequency of the series resonant circuit.
- 18. The combination as in claim 10 where said control means includes means establishing said pulse repetition frequency at a frequency greater than 20 KHz to avoid lamp hum.
- 19. The combination as in claim 1 where said duty cycle varying means is remotely located with respect to said control means.
- 20. The combination as in claim 1 where said resonant circuit is a series resonant circuit.
- 21. The combination as in claim 1 where said resonant circuit is a parallel resonant circuit.
- 22. The combination as in claim 10 where said resonant circuit includes at least one capacitor and at least one inductor and where said load means is connected in parallel with said capacitor.
- 23. The combination as in claim 22 where said lamp is connected in parallel with said capacitor.
- 24. The combination as in claim 23 where said lamp includes a pair of filaments, said capacitor being connected between said filaments.
- 25. The combination as in claim 24 where said resonant circuit includes said inductor, said filaments and said capacitor.
- 26. The combination as in claim 25 where said inductor, said filaments and said capacitor are connected in series.
- 27. The combination as in claim 26 where said pulse repetition frequencies of the pulse control trains are the substantially same as the resonant frequency of said inductor, said filaments and said capacitor.
- 28. The combination as in claim 10 including means for preventing the voltage across said lamp from exceeding a predetermined voltage.
- 29. The combination as in claim 28 including means for preventing the voltage across said lamp from exceeding a predetermined voltage.
SUMMARY OF THE INVENTION
This application is a continuation-in-part of application Ser. No. 061,109, filed 6/12/87, now abandoned.
It is recognized in the prior art that conventional core and coil ballasts for fluorescent lamps waste significant energy and generate unnecessary heat.
Additionally since core and coil ballasts operate on 50/60 Hz, alternating current line frequency variation, flickering of the fluorescent lamp and hum are a common problem. A detailed scientific evaluation of the performances of core and coil ballasts and solid-state ballasts has been reported by R. R. Verderber and O. Morse. See Performance of Electronic Ballasts and Other New Lighting Equipment, Lawrence Berkeley Laboratory, University of California, Report Prepared for the U.S. Department of Energy under Contract DE-AC03-76SF00098, October, 1985.
Accordingly, there has been a scientific endeavor to develop energy saving solid state electronic ballasts and circuitry for fluorescent lamps. A review of electronic ballasts is given in Energy User News, Sept. 8, 1986, p. 12; Energy User News, Aug. 1, 1983, p. 10; and J. E. Jewell, S. Selkowitz and R. R. Verderber. Solid-State Ballasts Prove to be Energy Savers, Lighting Design and Application, Vol. 10, No. 10, January 1980, pp. 36-42.
Existing solid-state dimming ballasts for fluorescent lamps have proven to be superior in efficiency to the core and coil ballasts; however, solid state ballasts also have attendant disadvantages. In addition to being relatively expensive, solid state ballasts have a comparable high failure rate, and produce significant amounts of electromagnetic radiation due to the presence of strong high frequency harmonics. A review of solid state ballasts is given in EBT.degree. s Electronic Ballasts. . . , Energy Users News, Vol. 9, Apr. 30, 1984, pp. 1 (3) and NTIS Energy Tech Notes, November, 1983, pp. 7-8.
The present invention is directed to a modified solid-state resonant converter switching circuit utilized as a dimming ballast for a fluorescent lamp. The improved circuit retains the advantages of the conventional resonant converter circuit and, at the same time, provides ideal excitation of the weakly ionized plasma mode on which fluorescent lamps operate. Thus, the modified convertor switching circuit constitutes an excitation source that is sinusoidal with zero current switching of the power switches. Moreover, constant filament voltage is provided to the fluorescent lamps.
The preferred embodiment of the electronic dimming ballast converter switching circuit in essence combines a modified resonant converter circuit with a radio frequency excited gaseous plasma circuit to obtain the various advantages described herein.
It is accordingly a principal object of the present invention to provide a new and improved electronic dimming ballast circuit for one or more fluorescent lamps, without the attendant disadvantages of the prior art, where the ballast utilizes the principles of a resonant power converter, for example, a serial or a parallel resonant converter having zero current switching through power switches and wherein the lamp excitation current is sinusoidal.
It is another object of the present invention to provide a new and improved electronic dimming ballast circuit for a fluorescent lamp that has improved power conversion efficiency.
A further object of the present invention is to utilize a resonant converter switching circuit to provide the excitation to multiple fluorescent lamps arranged in series, parallel or series/parallel; wherein the separate filament voltages to each of the fluorescent lamps is maintained constant; and wherein the circuit is operable at a high switching frequency to thereby eliminate hum and light flickering.
Other objects and features of the present invention will become apparent with a reading of the following specification when taken in conjunction with the drawings in which:
US Referenced Citations (8)
Foreign Referenced Citations (1)
| Number |
Date |
Country |
| 0655042 |
Mar 1979 |
SUX |
Non-Patent Literature Citations (2)
| Entry |
| "Siemens Consumer IC Data Book 1987/88", pp. 643-645 (copy submitted herewith). |
| "Siemens Energy and Automation", vol. 11, No. 2, March/April, 1985 (copy not available to Applicants). |
Continuation in Parts (1)
|
Number |
Date |
Country |
| Parent |
61109 |
Jun 1987 |
|
Patent Grant
4933605
