Fluorescent lamp ballast with adjustable lamp current

Details Fluorescent lamp ballast with adjustable lamp current Fluorescent lamp ballast with adjustable lamp current

1990-03-26

1991-04-02

Mis, David

Electric lamp and discharge devices: systems

Current and/or voltage regulation

315209R, 315244, 315284, 315DIG4, H05B 4129, H05B 4138

Patent

active

050049593

ABSTRACT:
A fluorescent lamp ballast comprises a self-oscillating inverter with saturable transformer means in its positive feedback circuit. The saturation flux density of the magnetic material used in this saturable transformer means determines the frequency of inverter oscillation. A permanent magnet is rotatably mounted adjacent the saturable transformer means and is used by way of cross-magnetization to adjustably affect the saturation flux density of the magnetic material, thereby correspondingly to adjust the frequency of oscillation: the more cross-magnetizing flux provided to the magnetic material from the permanent magnet, the smaller the saturation flux density and the higher the frequency of oscillation.
Current for the fluorescent lamp is attained from the inverter's squarewave voltage output by way of a series-excited parallel-loaded tuned L-C circuit, thereby providing for a lamp current of magnitude dependent upon the frequency of inverter oscillation. Thus, by adjusting the position of the permanent magnet, the magnitude of the lamp current can be adjusted over a wide range. In fact, in one of its extreme positions, the permanent magnet is operative to disable the inverter's self-oscillation, thereby entirely cutting off the lamp current.

REFERENCES:
patent: Re31758 (1984-12-01), Nilssen
patent: 3133256 (1964-05-01), Denelsbeck et al.
patent: 4045711 (1977-08-01), Pitel
patent: 4554487 (1985-11-01), Nilssen

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