howtodesignadimmingfluorescentelectronicballast| Application Note
How to design a dimming fluorescent electronic ballast
By Tom Ribarich, Director, Lighting Design Center, International Rectifier Power Management DesignLine (01/29/2006 11:04 PM EST) Dimming fluorescent lamps is an attractive feature that provides mood and brightness effects as well as having tremendous energy savings potential. Designing a dimmable electronic ballast, however, is a complicated and challenging task. This paper presents an overview for designing a dimming electronic ballast for a T5 35W lamp. Lamp requirements, dimming control methods, and resonant output stage design are all discussed in this paper. A new ballast design software program is also demonstrated which greatly aids with the design of the dimming ballast and generates the necessary schematic and bill of materials for prototyping. Finally, a fully-functional prototype is built, tested and compared against original design results. Lamp Requirements A fluorescent lamp requires preheating of the filaments, a high ignition voltage to strike, current or power control for dimming, and additi
onal filament heating during low dimming levels. To understand how a dimming fluorescent lamp works, a simple resistive model for the lamp is used (Figure 1). The lamp resistance (Rlamp) is connected between each filament resistor pair (R1, R2, R3 and R4).
Figure 1, Resistive lamp model
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