Using the FMS7401 to implement a 200-kHz full-digital dimming ballast for a fluorescent lamp
This application note describes how to use the FMS7401 digital power controller to implement a digitally-dimmed lamp ballast with a power range from 32 to 57 W.
This application note describes how to use the FMS7401
Digital Power Controller (DPC) to digitally implement a
power compact fluorescent lamp ballast with a power range
of 32–57W. The FMS7401 is designed to have a variable
frequency output pulse, such as Pulse Frequency
Modulation, (PFM), of 8- or 12-Bits resolution, as well
as a typical microcontroller feature including a sampled
8-bit A/D converter with an internal programmable memory.
The variable frequency is used for driving the series-resonant
network with a fluorescent lamp. By changing the driving
frequency, the lamp can be preheated for accurate preheating
time. For protection purposes, the lamp current is
monitored and can be controlled through a closed current
loop. The DPC can also identify any fault conditions such as
over-voltage, over-current, over-heat, strike fail, or broken
filament. Based on the programmable feature of the
FMS7401, a highly-intelligent ballast can be realized. A
32W full-digital ballast is designed for a power compact
fluorescent lamp from GE lighting with a running frequency
of 180KHz for maximum power and a pre-heating frequency
of 400KHz so as to reduce a bulky series inductor. The
experimental results are provided.
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