Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Periodic switch in the primary circuit of the supply...
Reexamination Certificate
1998-03-17
2001-07-03
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Periodic switch in the primary circuit of the supply...
C315S224000, C315S291000, C315S307000
Reexamination Certificate
active
06255783
ABSTRACT:
BACKGROUND
The present invention relates to power supplies for use with gas discharge lamps. More particularly, the present invention relates to a power supply for maintaining a constant brightness in a gas discharge lamp even in the presence of variations in input voltage to the power supply.
In general, conventional power supplies for a gas discharge lamp or tube limit the current provided to the lamp because the load corresponding to the lamp has a very low-slope impedance, which may be negative for certain values of input current, and which may lead to an unstable operating point for the tube.
Conventional power supplies for gas discharge lamps often do not compensate for variations in input voltage to the power supplies. Such variations in input voltage cause variations in the output current to the lamps, which result in variations in the brightness in the lamps as a function of the input voltage variations.
In many applications in which gas discharge lamps are used, it is desirable to have a reasonably constant brightness in the lamps even when fluctuations in input voltage occur. For example, in an application in which several power supplies are used together to power a lighting display formed of several lamps, with each power supply driving a separate lamp of the lighting display, the aesthetic value of the lighting display increases if the brightness or light intensity in each of the lamps is close in value. The lamps are usually connected by a parallel bus in a so-called “daisy chain” manner, such that the input voltage to a particular tube of the lighting display depends on the lamp's position on the bus. If the output current from each of the power supplies is not maintained at a reasonably constant value due to variations in the input voltage, then the brightness in each of the lamps in the lighting display will vary depending on its position on the bus.
OBJECTS AND SUMMARY OF THE INVENTION
In view of the above-mentioned considerations, it is an object of the present invention to provide a power supply for a gas discharge lamp that avoids the above-mentioned deficiencies.
It is another object of the present invention to provide a gas discharge lamp power supply that supplies a constant current to the lamp even when there are variations in the input voltage to the power supply.
It is also an object of the present invention to provide a gas discharge lamp power supply that operates at or close to the resonance point of the power supply.
According to an aspect of the present invention, a gas discharge lamp power supply includes an inverter for converting a DC input voltage to an AC input voltage, an inductor for limiting the current to the lamp, and a step-up transformer for providing a desired operating voltage to the lamp. The inverter includes a drive transformer which determines the operating frequency of the power supply. The power supply operates at or close to its resonance condition, and the current supplied to the lamp is within about 3% of the resonance current even for variations of about 20% in the DC input voltage to the power supply.
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Maioli Jay H.
Tran Thuy Vinh
Ventex Group LLC
Wong Don
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