PFC Control Theory

Figure 2-5. Hysteresis Current Control Mode Current Waveform

2.2.3 Digital Power Factor Concept — Discontinuous Conduction Mode

The control technique is based on discontinuous conduction mode with a current loop with a constant switching frequency (40 kHz) (see Figure 2-7).

The basic principles of the scheme are depicted in Figure 2-6. The PFC control algorithm includes two control loops, the same as the previous approach. The output voltage controller is implemented digitally using the MCU. A value proportional to the required input current is modulated by the PWM0 and is taken as an input to the current control loop, which is realized by the analog comparator. The comparator output is connected to the PWM fault pin that disables the PWM output. PWM1 is used directly for switching the MOSFET in order to maintain the required current value. PWM1 is switched off in every period where the reference sine wave signal generated by PWM0 is higher than the actual current sensed signal on the shunt resistor.

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

The discontinuous conduction mode PFC concept has several drawbacks — higher THD than hysteresis current control mode, non sinusoidal input current waveform, and the discontinuous conduction mode itself. The input current harmonics content, however, complies with EN 61000-3-2 standard.

The advantages are a simple control circuit, with low MCU resource consumption, and low losses.

Dimmable Light Ballast with Power Factor Correction, Rev. 1

Freescale Semiconductor

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Freescale Semiconductor M68HC08 manual Digital Power Factor Concept Discontinuous Conduction 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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