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Introduction
Dimmable Light Ballast with Power Factor Correction, Rev. 1
8 Freescale Semiconductor
• Energy saving
• Ease of adapting software for different lamps
• Ease of re-programming the system behavior
• Software can simplify the hardware
• Diagnostic functions — fault state, tube end-of-life, ignition fault, tube removed
• Open to innovation
The MC68HC908LB8 is designed for light ballast applications. It contains a HRP that is assigned to
control a lamp ballast circuit using half-bridge topology. The HRP provides two complementary outputs
for controlling a half-bridge drive. Pulse Width Modulation (PWM) with constant duty cycle is used for light
ballast control. The HRP frequency can be adjusted easily by software in range 40
kHz to 120 kHz in 256
steps. Dimming levels down to 5% are possible.
The PFC circuit uses an on-chip comparator on the MC68HC908LB8. This peripheral simplifies the
dimming light ballast solution with PFC, since it eliminates the need of external components and thus
decreases the system cost.
The reference design is intended for all geographic regions, so 110V/60Hz and 230V/50Hz input voltage
supplies are supported.
The application can be debugged using the MON08 CYCLONE debug tool in monitor mode.
WARNING
Since the application runs at high voltage, it is dangerous to connect
development tools directly to the board. Therefore, it is recommended
to use an opto-isolation monitor mode board. This separate board
provides an opto-isolated interface for the MON08 debug tool, using
the MON08 standard connector. This allows the user to safely debug
or examine code in-circuit.
1.3 The MC68HC908LB8 Microcontroller
The MC68HC908LB8 is a member of the low-cost, high performance MC68HC08 Family of 8-bit MCUs.
All MCUs in the family use the enhanced MC68HC08 central processor unit (CPU08) and are available
with a variety of modules, memory sizes and types, and package types.
Standard features of microcontroller MC68HC908LB8 are:
•8 MHz internal bus frequency
• Trimmable internal oscillator:
–4.0 MHz internal bus operation
– 8-bit trim capability
– 25% untrimmed
–2% trimmed
• 8K bytes of 10K write/erase cycle typical on-chip in application programmable FLASH
(1)
memory
with security option
• 128 bytes of on-chip random access memory (RAM)
1. Non volatile memory that retains its data when the power is removed.