Application Description

MAINS

FILTER

ZERO CROSSING

CONTROL BOARD

UREQ

USER INTERFACE

RECTIFIER

VOLTAGE

BUS-

DC

-

DC-BUS

PFC

DRIVER

POWER

SUPPLY

 

PWM

ACTUAL CURRENT

 

FILTER

 

PWM

+ -

GENERATION

 

HALF BRIDGE

DRIVER

PWM

HIGH

RESOLUTION

PWM

RESONANT

CIRCUIT

DIFFERENTIAL

VOLTAGE

CURRENT

CURRENT

1

2

FLUORESCENT LAMPS

MONITOR MODE

LUMINANCE LEVEL

e

sineGain

 

 

PI

 

 

REGULATOR

 

 

ireq

e

BRIGHTNESS

-

LINEARIZATION

MC68HC908LB8

fHRP

PI

REGULATOR

iact

TUBE

TUBE

CURRENT

PROCESSING e

Figure 3-1. Dimmable Light Ballast — System Concept

3.3.1 Light Ballast Control

The HRP provides two complementary PWM outputs for controlling a half-bridge in a light ballast application. It uses a dithering control method to provide a high step resolution (3.9 ns) from an 8 MHz input clock when driving inductive loads.

The High Resolution PWM Module (HRP) uses a dithering technique to increase the resolution of the output signal.The output switches between two frequencies or duty cycles at a programmable rate. By varying the percentage of time spent on each frequency/duty cycle, the output will appear to be at a value between the two dithering frequencies/duty cycles when driving an inductive load.

The advantage is easy implementation of a control method for half-bridge inverter using few external devices. The main advantage is simple performance using few instructions to perform the dithering control algorithm.

3.3.2 Power Factor Correction

The power factor correction circuitry provides the “sinusoidal” input current by controlling the PFC switch. In the control loop, the actual DC-bus voltage is compared with the desired one. The control error is processed by the PI (proportional-integral) controller, which generates the amplitude of the input “sinusoidal” current. The PWM generator generates the desired sinusoidal current profile using a PWM technique. The digital output signal is filtered by a passive filter and the resulting analog waveform is compared with the actual input current by an on-chip comparator. The comparator output controls directly

Dimmable Light Ballast with Power Factor Correction, Rev. 1

Freescale Semiconductor

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Freescale Semiconductor M68HC08 manual Light Ballast Control, Power Factor Correction

M68HC08 specifications

Freescale Semiconductor, known for its innovative solutions in the field of embedded systems, developed the M68HC08 microcontroller family, which includes the MC68HC908QT2. This 8-bit microcontroller is engineered to meet the demands of diverse applications, including automotive, industrial, and consumer electronics.

The MC68HC908QT2 is designed around Freescale’s M68HC08 core, which is renowned for its efficient and reliable performance. This microcontroller integrates a powerful instruction set, enabling developers to create high-performance applications with relatively low power consumption. The device operates at a clock frequency of up to 3 MHz, which is adequate for various control tasks.

One of the key features of the MC68HC908QT2 is its memory architecture. It includes a 2 KB Flash memory for program storage, representing a significant advantage for developers requiring non-volatile memory. Additionally, it encompasses 128 bytes of EEPROM memory, allowing for data retention even after power loss. The microcontroller also has 256 bytes of RAM for efficient data manipulation during operation.

In terms of input/output capabilities, the MC68HC908QT2 supports a variety of interfacing options. The microcontroller features up to 20 general-purpose I/O pins for flexibility in connecting with peripheral devices. Additionally, it provides multiple analog-to-digital converters (ADC) and timers that facilitate efficient analog signal processing and precise control through timing functions.

The architecture of the MC68HC908QT2 also incorporates sophisticated on-chip peripherals, enhancing its functionality. These peripherals include PWM (Pulse Width Modulation) outputs, which are essential for applications requiring motor control and other precise duty cycle processes. The integrated watchdog timer ensures reliable operation by resetting the system in the event of an application failure.

Moreover, the MC68HC908QT2 is equipped with an efficient power management system, enabling operation in a low-power mode, ideal for battery-powered applications. This microcontroller is packaged in a compact 28-pin dual in-line package (DIP), making it suitable for space-constrained designs.

In summary, the Freescale Semiconductor MC68HC908QT2 microcontroller is distinguished by its robust performance, extensive memory options, and versatile I/O capabilities. Its advanced features, including built-in timers, ADC, and a power management system, make it an exceptional choice for developers seeking to implement reliable and efficient embedded solutions. With its comprehensive architecture, the MC68HC908QT2 remains a popular choice in the landscape of 8-bit microcontrollers.