Ballast for discharge lamp

Details Ballast for discharge lamp Ballast for discharge lamp

2000-07-06

2001-12-25

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Current and/or voltage regulation

C315S307000, C315S224000, C315S2090SC

Reexamination Certificate

active

06333606

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ballast for a discharge lamp, and more particularly to a ballast for a discharge lamp adapted to prevent a flicker effect and acoustic resonant phenomenon generated in the lighting of high voltage discharge lamp, such as a metal lamp, sodium lamp and the like.
2. Description of the Prior Art
When a discharge lamp is lighted and after the lamp is lighted in a conventional ballast for discharge lamp, there is a problem in that the voltage and a current difference are generated due to discharge and resonant frequency variation, resulting in acoustic resonant phenomenon and flicker effect.
Particularly, there is another problem in that a voltage or a current characteristic differs a little bit even in discharge lamps of identical design that one manufactured by the same company, and such difference frequently changes resonant frequency of the discharge lamps, and there is great difficulty in solving the acoustic resonant phenomenon and flicker effect.
SUMMARY OF THE INVENTION
The present invention solves the aforementioned problems of the prior art and it is an object of the present invention to provide a ballast for a discharge lamp adapted to prevent resonant frequency of the discharge lamp from fluctuating due to voltage and current difference of the discharge lamp when the discharge lamp is lighted and after the discharge lamp is lighted, thereby avoiding the acoustic resonant phenomenon and flicker effect, and prolonging the life of the discharge lamp as well.
There is another object of the present invention to provide a ballast for a discharge lamp adapted to constantly maintain the resonant frequency of the discharge lamp even though intrinsic voltage and current characteristics of the discharge lamp are different, thereby preventing acoustic resonant phenomenon and flicker effect and prolonging life of the discharge lamp as well.
In accordance with the objects of the present invention, there is provided a ballast for discharge lamp, the ballast for discharge lamp fur utilizing high frequency voltage generated by alternatively switching two switching elements to light the discharge lamp, the ballast comprising:
a primary winding of a switching transformer to which the high frequency voltage is applied;
a secondary winding of a switching transformer for alternatively switching the two switching elements according to reverse electromotive voltage generated by application of high frequency voltage to the primary winding; and
stabilizing means for stabilizing reverse electromotive voltage generating at the secondary winding, wherein the stabilizing means comprises:
a control winding where reverse electromotive voltage is generated according to high frequency voltage applied to the primary winding;
a diode for half-rectifying the reverse electromotive voltage generated at the winding for control;
charging/discharging circuit for receiving the reverse electromotive voltage half-rectified by the diode to charge and discharge according to charging/discharging time constant; and
a transistor for switching according to a voltage value of the charge/discharge circuit to control reverse electromotive voltage generated at the secondary winding.


REFERENCES:
patent: 5394062 (1995-02-01), Minarczyk et al.
patent: 5406177 (1995-04-01), Nerone
patent: 5426348 (1995-06-01), Qi
patent: 5539281 (1996-07-01), Shackle et al.

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