Control Theory

2.2.2 Digital Power Factor Concept — Hysteresis Current Control Mode

The control technique is based on hysteretic current control. The system operates in continuous conduction mode with variable switching frequency (30–100 kHz) (see Figure 2-5).

This PFC concept is designed to have the minimum of MCU performance requirements. The basic principles of the scheme are depicted in Figure 2-4. The PFC control algorithm includes two control loops, a fast one for input current control and a slow one for output voltage control. The output voltage controller is implemented digitally using the MCU. A value proportional to the required input current is modulated by the PWM and is taken as an input to the current control loop, which is realized by the analogue comparator. The comparator switches the MOSFET in order to maintain the required current value.

The desired shape of the input current is a sine wave. The generated current waveform is shown in Figure 2-8.

A hysteresis current control mode PFC concept has several drawbacks, including variable MOSFET switching frequency, non sinusoidal input current waveform and switching under current, which causes higher losses than other PFC topologies.

The input current harmonics content, however, complies with EN 61000-3-2 standard.

The advantages are simple control circuit, low MCU resources consumption, continuous conduction mode operation, and low total harmonic distortion (THD).

0

AC Line Voltage

AC Line Current

L

Zero

Crossing

AC

DC Bus

Voltage

IC ADC

+ DC BUS

Comparator

+MOSFET

AC

LINE

DC

PWM Reference Voltage

-

+

MCU

Actual

Current

Current Sensing

 

GND

 

 

 

Figure 2-4. Hysteresis Current Control Mode Principle

Dimmable Light Ballast with Power Factor Correction, Rev. 1

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Freescale Semiconductor

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Freescale Semiconductor M68HC08 manual Digital Power Factor Concept Hysteresis Current Control Mode
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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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