EVLB001 Datasheet, PDF (4/35 Pages) ATMEL Corporation – Automatic microcontroller dimmable ballast

Figure 1-1. Fluorescent Tube Composition
Introduction
Since the argon conductivity increases and resistance across the lamp ends decreases
as the gas becomes excited, an inductance (ballast) must be used to limit and control
the gas current. In the past, an inductor could be designed to limit the current for a nar-
row range of power voltage and frequency. A better method to control gas current is to
vary an inductor’s volt-seconds to achieve the desired lamp current and intensity. A vari-
able frequency inverter operating from a DC bus can do this. If the inductor is part of an
R-L-C circuit, rapid start ignition currents, maximum intensity, and dimming currents are
easily controlled depending on the driving frequency versus resonant frequency.
A ballast should include a power factor corrector (PFC) to keep the main current and
voltage in phase with a very low distortion over a wide range of 90 to 265 VAC 50/60 Hz.
With microcontroller control, economical remote analog or digital control of lamp func-
tion and fault reporting are a reality. Moreover, adjusting the lamp power to correspond
with human perceived light level is possible. An application specific microcontroller
brings the designer the flexibility to increase performance and add features to the light-
ing product. Some of the possible features are described here in detail. The final design
topology is shown in the block diagram of Figure 2-1.
Now, a new way of dimming fluorescent lamps fills the incandescent/fluorescent feature
gap plus adds many additional desirable features at a very reasonable cost.
ATAVRFBKIT / EVLB001 User Guide
1-2
7597B–AVR–10/07