Pretty much all (somewhat inaccurately named) electronic ballasts for fluorescent lamps run off a DC voltage and have to convert it into AC to operate the lamp.
The DC supply can come from rectified AC mains (as seen in standard compact fluorescent lamps) or from a low-voltage bus or battery (as seen in the interior lights of camping vehicles, laptop screen backlights or emergency lamps).
How are the circuits built that achieve the DC-to-AC conversion?
Answer
The book, Practical Eco-Electrical Home Power Electronics published by Elektor has a chapter on CFL inverters with some circuit diagrams of reverse-engineered inverters and an engineering explanation of how they work. See Practical Eco-Electrical Home Power Electronics published by Elektor.
The fluorescent tube has different circuit models when lit and unlit and they correspond to two different resonant modes which the inverter must accommodate in its design. After tearing apart multiple CFLs, I find the design is well-standardized as given in the previous answer for battery-powered lighting, and as a half-bridge (preceded sometimes by a voltage doubler) for line-operated CFLs.
All these inverters are resonant and when the bulb is not lit, depend on its capacitance to set the resonant frequency. Once lit, the bulb has a low-value of resistance and a capacitor in series with the bulb determines the series resonant frequency.
No comments:
Post a Comment