Software Design

5.2.1 Power Factor Correction Control

PFC control consists of DC-bus voltage control using the PI controller, phase shift synchronization, reference sine wave generation and generation of output PFC control signals. It also includes the trimming of the internal oscillator frequency according to the frequency of the mains provided.

5.2.1.1 DC-bus Voltage Control

The actual value of the DC-bus voltage is sensed by the AD converter. This value is compared with the required DC-bus value. The regulation error is then the input value for the PI regulator. The output value from the PI regulator is the reference sine wave gain. The PWM module generates a reference sine wave with calculated amplitude. The filtered reference sine wave is compared with the actual current using the on-chip comparator. For the hysteresis current control mode HW variation, the output from the comparator is the switching signal for the PFC MOSFET transistor. For the discontinuous conduction mode HW variation, the output comparator is connected to the PWM fault pin. The PWM1 signal is directly used for switching the PFC MOSFET transistor.

5.2.1.2 Phase Shift Synchronization

Phase shift synchronization synchronizes the generated PFC reference sine wave to the frequency of the mains. It is realized by means of:

•Zero voltage crossing detection (zero voltage sensor)

The zero voltage crossing sensor generates a falling edge every time when the input voltage crosses zero from positive to negative polarity.

•External interrupt

An external interrupt is triggered by the zero voltage crossing sensor. The interrupt subroutine is used to get the content of timer TIM registers TCNTH:TCNTL for automatic microcontroller trimming and for PFC reference sine wave amplitude gain calculation in lamp run mode.

•MCU oscillator frequency trimming

For microcontroller automatic trimming, the timer TIM is used as an interval counter. The timer is incremented by the internal clock (divided by prescaler). Its content is cleared every IRQ interrupt produced by the voltage zero crossing sensor. A user defined value determines what number should be found in TIM registers TCNTH:TCNTL. On the basis of the comparison between required and actual counter values, the content of the oscillator trim register OSCTRIM is adjusted with ramp.

5.2.1.3 Reference Sine Wave Generation

Reference is performed by the PWM peripheral. The software contains a sine wave table with values for interval and maximum amplitude. The amplitude of the sine wave depends on the value of the DC-bus voltage and it is adjusted by the PI controller every 20ms. Two different sets of PI controller parameters are used, one for MCU startup, when the DC-bus voltage must reach the required value quickly and HRP is not activated, and the second during standard running operation.

5.2.1.4 Generation of Output PFC Control SIgnal

The generated output PFC signal controls the PFC power MOSFET. An on-chip operational amplifier is used in comparator mode. It compares the reference sine wave, filtered by the RC filter, with the actual current and generates a switching signal for the PFC MOSFET transistor in the hysteresis current control mode HW variation. In discontinuous conduction mode comparator output is used for switching off the PWM1 signal. It works as a fault detection in fact. When the actual current sensed on the shunt resistor

Dimmable Light Ballast with Power Factor Correction, Rev. 1

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Freescale Semiconductor

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Freescale Semiconductor M68HC08 manual Power Factor Correction Control, DC-bus Voltage Control
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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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