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Table 3-1. Light Ballast Characteristics
Parameter Unit Value
Lamp Type F18W/33
Input Power W 8...31
Input Current
(230VAC)
mA 40...290
Preheat Output
Frequency
kHz 86
Preheat Output
Voltage
Vpp 345
Preheat Time ms 900
Running Output
Frequency Range
kHz 50...100
Running Output
Voltage Range
V 200...235
Input AC Voltage VAC 110V/60Hz, 230/50Hz
Ambient
Temperature Range
°C 0.50
Power Factor 0.94...0.99
Total Harmonic
Distortion
% 5.2...24.6
Output Ignition
Voltage
Vpp 510
Reference Design
Dimmable Light Ballast with Power Factor Correction, Rev. 1
22 Freescale Semiconductor
3.3 Application Description
The system concept is shown in Figure 3-1. The system consists of:
• Control board with MC68HC908LB8 microcontroller
• Two fluorescent lamps
The MC68HC908LB8 MCU runs the main control algorithm. According to the dimming level potentiometer
It generates output signals for the half-bridge inverter which controls the ballast circuit. It also controls
PFC. The desired dimming value is set by the potentiometer, because the human eye is more sensitive
at lower light levels. The input values from the potentiometer are converted using brightness linearization.
The HRP uses a frequency control method for dimming. It incorporates hardware that allows dithering
between two adjacent frequencies for smooth light level dimming.