Freescale Semiconductor M68HC08 manual Application Description, 1.Light Ballast Characteristics

Reference Design

Table 3-1. Light Ballast Characteristics

Parameter	Unit	Value
Lamp Type		F18W/33
Input Power	W	8...31
Input Current	mA	40...290
(230VAC)
Preheat Output	kHz	86
Frequency
Preheat Output	Vpp	345
Voltage
Preheat Time	ms	900
Running Output	kHz	50...100
Frequency Range
Running Output	V	200...235
Voltage Range
Input AC Voltage	VAC	110V/60Hz, 230/50Hz
Ambient	°C	0.50
Temperature Range
Power Factor		0.94...0.99
Total Harmonic	%	5.2...24.6
Distortion
Output Ignition	Vpp	510
Voltage

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.

Dimmable Light Ballast with Power Factor Correction, Rev. 1

22 Freescale Semiconductor