Hardware Design

Figure 4-2. Dimmable Light Ballast with Hysteresis PFC HW variation — Hardware Block Diagram

4.2.1 Input and PFC

The input and the PFC part provide the DC-bus voltage to supply the inverter. The schematic for hysteresis current control mode is shown in Figure 4-3. The difference in discontinuous conduction mode against hysteresis mode is that the gate of Q4 is connected to pin PWM1 of the MCU (see Figure A-2), not to the output of the comparator. The input stage consists of an EMI filter and a single-phase full-bridge rectifier. Although the PFC regulator is called an active filter, it does not suppress all harmonics. For this reason, the EMI filter is placed at the input.

The PFC is based on the most popular non transformer isolated DC-DC boost (step-up) converter topology. The PFC stage is built with input inductor L1, power MOSFET switch Q1, output rectifier diode D1, and output capacitor C4. Capacitor C3 performs a filtering function. The input stage converts the mains AC voltage, rectified by the diode bridge U1, to an output DC voltage on the output capacitor C4. The current flowing through inductor L1 is sensed by the current sense resistor R4. There are two different values of resistor R4, 1.5Ω for rectified input voltage lower than half of DC-Bus voltage and 2.7Ω for higher voltage. The voltage drop over the current sense resistor corresponds to the measured current. The circuit, with resistors R3, R5, R7, R9, diodes D2 and D15, and capacitor C27 works as a mains zero-crossing detector. It senses rectified mains voltage and generates zero-crossing pulses with an amplitude of 5 volts. With the help of this detector, the microcontroller synchronizes its operation with the mains frequency.

The DC-bus voltage sensor consists of resistors R1, R2, R6, and R8. It senses the output voltage of the PFC, and its output is connected to the MCU AD converter. In hysteresis current control mode the output

Dimmable Light Ballast with Power Factor Correction, Rev. 1

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Freescale Semiconductor

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Freescale Semiconductor M68HC08 manual Input and PFC
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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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