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1.1
General
Description
1.2
Ballast
Demonstrator
Features
-2
7629A–AVR–04/06
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 mains 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 and operating currents are easily controlled depending
on the driving frequency versus resonant frequency.
Utility is enhanced by designing a power factor correcting boost converter (PFC) to
achieve the inverter DC bus over a wide mains voltage range of 90 - 265VAC, 50/60 Hz.
Since a PFC circuit keeps the mains current and voltage in phase with very low distor-
tion, mains power integrity is maintained. Additional utility is achieved by designing a
microcontroller for the electronic ballast application that can precisely and efficiently
control power levels in the fluorescent lamp. An application specific microcontroller
offers the designer unlimited opportunity to enhance marketability of lighting products.
The final design topology is shown in the block diagram of Figure 1-3.
Fluorescent ballast topology usually includes line conditioning for CE compliance, a
power factor correction block including a boost converter to 380 V for universal input
applications and a half bridge inverter. Varying the frequency of the inverter permits time
for filament preheat and ignition for rapid starting, including precise power control. As
shown in the block diagram, figure 3, all of these functions can be timed, regulated, and
diagnosed with the Atmel AT89EB5114 microcontroller.
• Automatic microcontroller non-dimmable ballast
• Universal input _ 90 to 265 VAC 50/60 Hz, 90 to 370 VDC
• Power Factor Corrected (PFC) boost regulator
• Power feedback for stable operation over line voltage range
• Variable frequency half bridge inverter
• 18W, up to 2 type T8 lamps
• Automatic single lamp operation
Ballast Demonstrator User Guide
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