Claims
- 1. An apparatus for driving a fluorescent lamp, comprising:
- a pulse width modulator having a frequency control input and having a pulse modulated output at a frequency responsive to said frequency control input;
- a transformer having a primary and a secondary, said secondary generating a voltage connectable to the fluorescent lamp;
- at least first and second semiconductor switches responsive to said pulse modulated output which directly drive the primary of said transformer with a substantially rectangular wave voltage;
- a sensor which senses whether current is flowing through said secondary of said transformer and through the fluorescent lamp and which generates an output indicative of whether current is flowing; and
- a frequency control circuit which receives said output of said sensor and which generates said frequency control input to said pulse width modulator, said frequency control circuit maintaining said frequency control input substantially constant when current is flowing in the lamp, said frequency control circuit varying said frequency control input when no current is sensed to thereby sweep said frequency of the pulse modulated output from a low frequency to a high frequency to cause the secondary output voltage of the transformer to increase to thereby strike the fluorescent lamp.
- 2. The apparatus of claim 1 further comprising said fluorescent lamp.
- 3. The apparatus of claim 1 wherein said fluorescent lamp is a cold cathode fluorescent lamp.
- 4. The apparatus of claim 3 wherein said cold cathode fluorescent lamp provides lighting for a flat panel display.
- 5. The apparatus of claim 4 wherein said flat panel display is in communication with a computer.
- 6. The apparatus of claim 3 wherein said cold cathode fluorescent lamp provides lighting for a scanner.
- 7. The apparatus of claim 6 wherein said scanner is in communication with a computer.
- 8. A method of starting a fluorescent lamp coupled to the secondary of a transformer, comprising:
- sensing that no current is flowing through the lamp;
- applying a series of pulses to a primary of the transformer at a pulse repetition frequency, the series of pulses causing the secondary of the transformer to have an output voltage, said pulse repetition frequency having an initial pulse repetition frequency;
- sweeping the pulse repetition frequency of the series of pulses from said initial pulse repetition frequency up to a higher pulse repetition frequency while sensing for current through the lamp; and
- when current is sensed in the lamp, maintaining the pulse repetition frequency at the initial pulse repetition frequency.
- 9. The method of claim 8, wherein when the pulse repetition frequency reaches the higher pulse repetition frequency, the pulse repetition frequency is reduced to the initial pulse repetition frequency and the pulse repetition frequency is again increased.
- 10. The method of claim 9, wherein the pulse repetition frequency is repeatedly increased to the higher pulse repetition frequency and returned to the initial pulse repetition frequency until current is sensed in the lamp.
- 11. A method of starting a fluorescent lamp comprising:
- applying a signal at a first frequency to a primary of a transformer to generate a first voltage at a secondary of said transformer;
- sweeping said signal to a second frequency, said second frequency generating a second voltage at said secondary which is greater than said first voltage; and
- decreasing said signal to a frequency below said second frequency in response to a current in a fluorescent lamp.
- 12. The method of claim 11 further comprising decreasing said signal below said second frequency once said signal reaches said second frequency.
- 13. The method of claim 12 wherein increasing said signal and decreasing said signal are repeated until said current exists in said fluorescent lamp.
- 14. The method of claim 13 wherein increasing said signal and decreasing said frequency are repeated to reduce heating in said transformer.
- 15. The method of claim 11 wherein said signal is generated with a sawtooth waveform.
- 16. The method of claim 11 further comprising operating a flat panel display with said fluorescent lamp.
- 17. The method of claim 11 further comprising operating a scanner with said fluorescent lamp.
- 18. An apparatus for driving a fluorescent lamp, comprising:
- a transformer having a primary and a secondary, said primary in communication with an input signal, said secondary configured to generate a voltage in response to a frequency of said input signal;
- a sensor which is configured to generate an output indicative of whether current is flowing in a fluorescent lamp; and
- a control circuit in communication with said sensor, said control circuit configured to periodically sweep the frequency of said input signal when said sensor does not indicate current is flowing, said control circuit further configured to decrease said frequency of said input signal when said sensor indicates that current is flowing.
- 19. The apparatus of claim 18 wherein said control circuit periodically decreases and increases said frequency of said input signal when said sensor does not indicate current is flowing.
- 20. The apparatus of claim 18 further comprising at least first and second semiconductor switches which drive said primary of said transformer with a substantially rectangular wave voltage.
- 21. The apparatus of claim 20 further comprising a pulse width modulator having a frequency control input and having a pulse modulated output at a frequency responsive to said frequency control input and wherein said pulse modulated output drives said first and second semiconductor switches.
- 22. The apparatus of claim 21 wherein said control circuit generates said frequency control input to said pulse width modulator.
- 23. The apparatus of claim 18 wherein said control circuit is configured to maintain said frequency of said input signal substantially constant when said sensor indicates current is flowing.
- 24. The apparatus of claim 18 further comprising said fluorescent lamp.
- 25. The apparatus of claim 24 wherein said fluorescent lamp is a cold cathode fluorescent lamp.
- 26. The apparatus of claim 24 wherein said fluorescent lamp provides lighting for a flat panel display.
- 27. The apparatus of claim 26 wherein said flat panel display is in communication with a computer.
- 28. The apparatus of claim 24 wherein said fluorescent lamp provides lighting for a scanner.
- 29. The apparatus of claim 28 wherein said scanner is in communication with a computer.
- 30. An apparatus for driving a fluorescent lamp, comprising:
- a transformer means having a primary and a secondary, said primary in communication with an input signal, said secondary configured to generate a voltage in response to the frequency of said input signal;
- a sensor means for generating an output indicative of whether current is flowing in a fluorescent lamp; and
- a control means in communication with said sensor means for sweeping the frequency of said input signal when said sensor means does not indicate current is flowing, said for decreasing said frequency of said input signal when said sensor means indicates that current is flowing.
- 31. The apparatus of claim 30 wherein said control means periodically decreases and increases said frequency of said input signal when said sensor does not indicate current is flowing.
- 32. The apparatus of claim 30 further comprising switching means for driving said primary of said transformer with a substantially rectangular voltage waveform.
- 33. The apparatus of claim 32 further comprising a modulator means for driving said switching means, said modulation means having a frequency control input and having a pulse modulated output at a frequency responsive to said frequency control input.
- 34. The apparatus of claim 1 wherein said frequency control input comprises a variable resistance.
- 35. The apparatus of claim 1 wherein said frequency control circuit periodically inhibits said pulse modulated output.
- 36. The apparatus of claim 1 wherein said sweeping increase of said frequency of said pulse modulated output is periodic.
- 37. The apparatus of claim 1 wherein said frequency control circuit further comprises a sawtooth generator which causes said sweeping increase of said frequency of said pulse modulated output.
- 38. The apparatus of claim 1, further comprising a soft start mechanism which adjusts a duty cycle of the pulse modulated output.
- 39. The method of claim 8, further comprising inhibiting the series of pulses to the primary of the transformer.
- 40. The method of claim 8, further comprising adjusting a duty cycle of the series of pulses.
- 41. The method of claim 11 wherein said second frequency is a minimum frequency required to cause said fluorescent lamp to strike.
- 42. The method of claim 11, further comprising inhibiting said signal to said primary of said transformer.
- 43. The method of claim 11, further comprising adjusting a duty cycle said signal to said primary of said transformer.
- 44. The apparatus of claim 18, further wherein said control circuit inhibits said input signal.
- 45. The apparatus of claim 18, further wherein said control circuit adjusts a duty cycle of said input signal.
- 46. The apparatus of claim 30 where said control means further comprises means for inhibiting said input signal.
- 47. The apparatus of claim 30 where said control means further comprises means for adjusting a duty cycle of said input signal.
RELATED APPLICATION
This application claims the benefit of priority under 35 U.S.C. .sctn. 119(e) of U.S. Provisional Application No. 60/040,758, filed Mar. 14, 1997.
US Referenced Citations (30)