Chapter 2

Control Theory

2.1 Introduction

This chapter covers fluorescent lamp theory and two PFC concepts - discontinuous conduction mode and hysteresis current control mode.

2.1.1 Fluorescent Lamp Control Theory

To light a low-pressure fluorescent lamp, the electronic circuit must perform the following four main functions:

•Provide a startup voltage across the electrodes of the lamp

•Maintain a constant current when the lamp is operating in the steady state

•Ensure that the circuit will remain stable, even under fault conditions

•Comply with the applicable domestic and international regulations (PFC, THD and safety)

Most generally, light ballast topology fairly closely matches target lamps in terms of tube wattage, length, and diameter. The digital electronic lamp ballast includes also additional features like dimming capability, tube end-of-life, startup fault, tube removed indication, and so on. Different tubes require different software settings; also, some hardware components may have to be adapted accordingly.

2.1.2 Fluorescent Lamp Operation

When the lamp is off, no current flows through the tubes, and the apparent impedance is nearly infinite.

When the voltage across the electrodes reaches the Vstrike value, the gas mixture is highly ionized and an arc is generated across the two terminals of the lamp. This behavior is depicted by the typical operating

curve shown in Figure 2-1.

Dimmable Light Ballast with Power Factor Correction, Rev. 1

Freescale Semiconductor

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Freescale Semiconductor M68HC08 manual Fluorescent Lamp Control Theory, Fluorescent Lamp Operation
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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.
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