Ballast circuit for fluorescent lamp
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United States of America Patent
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Sep 21, 1999
Issued Date -
N/A
app pub date -
Aug 1, 1997
filing date -
Sep 30, 1994
priority date (Note) -
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Abstract
An improved ballast circuit for use with a compact fluorescent lamp includes an EMI filter, a rectifier and voltage amplification stage, an active resonant circuit and power factor correction stage which is connected in parallel to a lamp load. The ballast circuit includes a feedback capacitor which provides a feedback path for a portion of the high frequency current to the rectifier and voltage amplification stage. The feedback capacitor of the improved ballast circuit reduces the non-linear characteristics of the diode, thus providing almost a linear load on the input power supply and therefore achieving an improved power factor, on the order of 0.95 or greater. The improved ballast circuit may also include a dimming stage which works with the active resonant circuit to vary the amount of power that is supplied to the lamp load. The dimming stage does not require the addition of parasitic active stages and thus provides a lamp with high electrical efficiency.
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