Electric lamp and discharge devices: systems – Current and/or voltage regulation – Automatic regulation
Patent
1998-04-02
2000-09-12
Philogene, Haissa
Electric lamp and discharge devices: systems
Current and/or voltage regulation
Automatic regulation
315291, 315209R, 315244, 315247, 315DIG4, 315DIG7, G05F 100
Patent
active
061182281
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the supply of power for fluorescent lamps. More specifically, the invention pertains to a high-frequency filtered and dimmable electronic ballast circuit for use with low-pressure fluorescent lamps. The circuit contains an input protection means, a radio-frequency filter means connected to the output of said protection means, a rectifier means connected to the output of said radio-frequency filter means, a power factor correcting switching power supply means connected to the output of said rectifier means, a current controlled push-pull converter means connected to the output of said switching power supply means, one or more series-parallel resonant filter means connected to the output of the said push-pull converter means and fluorescent lamp means connected to the output of said resonant filter means.
BACKGROUND OF THE INVENTION AND PRIOR ART
Low-pressure fluorescent tubes, so technical solutions for their electronical starting and powering are well known and have been widely used for several decades. Most of prior art solutions are designed and build as an ON/OFF (two-state) switch for the sake of simplicity and low-cost: the fluorescent lamp is either switched on or switched off and their light input intensity cannot be dimmed neither within ranges nor continuous.
Low-pressure fluorescent lamps and ballasts for their electrical starting and powering are well known technology and various types of fluorescent lamp and ballast combinations have been widely used for several decades. Most older magnetic ballasts contain passive components only, provide voltage outputs in the 50 Hz to 60 Hz frequency range are subject to start-up and running flicker and operate extremely inefficiently. Newer electronic ballasts utilize active electronic switching circuits, provide high-frequency voltage outputs in the 20 kHz to 50 kHz frequency range and operate more efficiently. However, most electronic ballasts are very simple in design, have insufficient input protection and radio-frequency filtering, operate at poor input power factors, inject large amounts of low-frequency harmonics back into the ac supply, have square-wave voltage outputs, utilize feed-back control to maintain the output voltage constant and are suitable only to operate in the ON/OFF mode (i.e.: non-dimming). Such ballasts eliminate start-up and running flicker but do not operate very reliably and, in addition, may cause severe reductions in lamp lifetimes since it is well known that one of the major causes of reduced lamp lifetime is the result of subjecting the lamp filaments to high-voltage square-wave excitation. Some of the latest types of electronic ballast designs have attempted keep the excitation quasi-sinusoidal by resonating the output square-waves with series resonant circuits. The load impedance of the lamp in such circuits is generally an integral part of the series resonant circuit and different ballasts are required to power fluorescent loads with different impedances. Output voltage is sensed and feedback is used to modulate the square-wave to maintain output voltage relatively constant during load impedance changes. If, during normal ON operation, a lamp load is removed from such a circuit, the output voltage across the remaining lamp and across the feedback circuit may become very high and result in the damage of the remaining lamp, the converter's electronic circuits and also pose a potential risk to the user.
As an example of latest technology, U.S. Pat. No. 4,933,605, discloses a high frequency dimmable electronic ballast circuit for low-pressure fluorescent lamps. The circuit has a dc power supply, a converter connected to the power supply for preparing a square-wave ac voltage, a series-resonant output circuit with the fluorescent lamp load connected directly in series (or via a transformer) with the resonant circuit. Accordingly, the lamp is an integral part of the resonance circuit used to force the waveform of the voltage between the lamp filaments to be quasi-sine w
REFERENCES:
patent: 5214356 (1993-05-01), Nilssen
patent: 5371440 (1994-12-01), Liu et al.
patent: 5402043 (1995-03-01), Nilssen
patent: 5519289 (1996-05-01), Katyl et al.
Kelemen Gabor J.
Philogene Haissa
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