DRIVING CIRCUIT AND METHOD FOR FLUORESCENT LAMP

Abstract

Disclosed is a driving circuit and method for a fluorescent lamp. The driving circuit comprises a power factor correction (PFC) stage, a startup stage, an isolation stage, a square-wave driving stage and an output stage. The PFC stage receives and converts an input alternating current (AC) voltage into a direct current (DC) voltage. The startup stage receives the DC voltage and adjusts the DC voltage into an operating voltage. The startup stage is connected in parallel with the square-wave driving stage. The square-wave driving stage is connected to the isolation stage and converts the operating voltage into a boosted square-wave voltage, and the output stage receives the boosted square-wave voltage to ignite the fluorescent lamp. As such, the fluorescent lamp may be rapidly and properly ignited.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of the preferred embodiments, is better understood when read in conjunction with the appended drawings. It is understood, however, that the invention is not limited to the specific methods disclosed or illustrated. In the drawings:

FIG. 1 is an experimental waveform of a lamp current of a prior art fluorescent lamp using burst mode dimming technique;

FIG. 2 is an experimental waveform of a lamp voltage of a prior art fluorescent lamp using frequency varying technique;

FIG. 3 is a functional block diagram of a driving circuit of a fluorescent lamp according to the present invention;

FIG. 4 is a schematic view of the driving circuit of a fluorescent lamp according to a first embodiment of the present invention;

FIG. 5 is a signal waveform plot associated with the driving circuit shown in FIG. 3;

FIG. 6 is a schematic view of the driving circuit of a fluorescent lamp according to a second embodiment of the present invention;

FIG. 7 is a flowchart illustrating a method for driving a fluorescent lamp according to the present invention; and

FIG. 8 is an experimental waveform of a lamp current of a fluorescent lamp applied with the burst mode dimming technique according to the present invention.

Claims

1. A method for driving a fluorescent lamp, comprising the steps of: generating a direct current (DC) voltage;boosting the DC voltage to be an operating voltage according to a pulse-wave input;stopping the pulse-wave input and converting the operating voltage to a boosted voltage when the operating voltage reaches a start-up voltage; andigniting the fluorescent lamp by using the boosted voltage.

2. The method according to claim 1, wherein the step of generating comprising the step of: receiving an alternating current (AC) voltage; andconverting the AC voltage into the DC voltage by using a power factor correction (PFC) circuit.

3. The method according to claim 1, wherein the step of igniting comprises the steps of: adjusting the boosted voltage into a final boosted voltage; andigniting the fluorescent lamp by using the final boosted voltage.

4. The method according to claim 1, wherein the fluorescent lamp is one of a non-flat fluorescent lamp and a flat fluorescent lamp.

5. The method according to claim 4, wherein the flat fluorescent lamp is one of a mercury-containing flat fluorescent lamp and a mercury-free flat fluorescent lamp.

6. A circuit for driving a fluorescent lamp, comprising: a power factor correction (PFC) stage receiving an alternating current (AC) voltage and adjusting the AC voltage into a direct current (DC) voltage;a start-up stage receiving the DC voltage and boosting the DC voltage to be an operating voltage;an isolation stage;a square-wave driving stage being isolated from the PFC stage with the isolation stage and adjusting the operating voltage into a boosted voltage when the operating voltage reaches a start-up voltage; andan output stage receiving and boosting the square-wave voltage into a boosted square-wave voltage and igniting the fluorescent lamp by using the boosted square-wave voltage,wherein the square-wave driving stage is initialized and the start-up stage is stopped when the operating voltage reaches the start-up voltage.

7. The circuit according to claim 6, wherein the PFC stage comprises a capacitor for storing the DC voltage.

8. The circuit according to claim 6, wherein the start-up stage is one of a voltage boost converter and a fly-back converter.

9. The circuit according to claim 8, wherein the fly-back converter is one of a Cuk converter, a single-ended primary inductor circuit (SEPIC) converter and a Zeta converter.

10. The circuit according to claim 6, wherein the square-wave driving stage is connected in parallel with the start-up stage.

11. The circuit according to claim 10, wherein the isolation stage is selected from the group consisting of a diode, a capacitor, a resistor, an inductor and an isolating transformer.

12. The circuit according to claim 6, wherein the square-wave driving stage is selected from the group consisting of a half-bridge driving circuit, a full-bridge driving circuit and a push-pull circuit.

13. The circuit according to claim 6, wherein the square-wave driving stage comprises a low voltage side of a transformer on which the square voltage exists and the output stage comprises a high voltage side of the transformer receiving and coupling the boosted square-wave voltage into a transformed square-wave voltage and a resistance and capacitance unit through which the fluorescent lamp is ignited.

14. The circuit according to claim 13, wherein the resistance and capacitance unit comprises a load resistor set being an internal resistance of the fluorescent lamp and a load capacitor set connected in series therewith.

15. The circuit according to claim 14, wherein the load resistor set comprises a load resistor.

16. The circuit according to claim 14, wherein the load capacitor set comprises a load capacitor.

17. The circuit according to claim 6, wherein the fluorescent lamp is one of a non-flat fluorescent lamp and a flat fluorescent lamp.

18. The circuit according to claim 17, wherein the planar fluorescent lamp is one of a mercury-containing flat fluorescent lamp and a mercury-free flat fluorescent lamp.

19. A circuit for driving a fluorescent lamp, comprising: direct current (DC) voltage generating unit receiving an alternating current (AC) generating and generating a DC voltage;DC voltage boosting unit receiving a pulse-wave input boosting the DC voltage into an operating voltage according to the pulse-wave input;pulse-wave input stopping unit stopping the pulse-wave input when the operating voltage reaches a start-up voltage;square-wave voltage generating unit converting the operating voltage to a boosted voltage when the operating voltage reaches the start-up voltage; andlamp igniting unit igniting the fluorescent lamp by using the boosted voltage.

20. The circuit according to claim 19, wherein the DC voltage generating unit and the square-wave voltage generating unit are isolated with an isolating unit.