Hardware Design

4.2.2 Inverter

The power inverter generates the proper voltage for the fluorescent tubes. The power inverter consists of two MOSFET transistors driven by a half-bridge driver. It incorporates the half-bridge, a resonant circuit, different voltage and tube current sensing, and output inductance circuity.

The half-bridge driver IR2106 from International Rectifier is electrically connected according to the manufacturer’s recommendations. The half-bridge is supplied from the DC-bus voltage. It is controlled by the TOP and BOT signals from the MCU.

The half-bridge lamp resonant circuit consists of capacitor C15 and inductance L7. It provides preheating, ignition, and running operating conditions by changing the operating frequency.

The tube voltage difference circuit consist of coils L3A, L3B, and L3D, resistors R21, R24, R22, and R151, diode D8, and capacitor C17, and is used to sensing voltage differences between lamps. It helps to recognize aging of the lamps.

Coils L4 and L5 and diodes D4 and D5 are for filament preheating. Diodes maintain a small offset to remove the flickering effect. Coils L3A and L3D balance possible differences in current flow into tubes, mainly at ignition stage. Devices R19, D7, R152, D6, C16, and R20 sense the current flow in tube 1 (and similarly for tube 2).

For different tubes parameters, the tube currents are different. The ignition circuit formed by L3D, L3A, and R17 balance the current. The compensation current flows through R17 until the tube currents are equal, at which time the ignition of both tubes can be done reliably.

Tubes preheating heats the tubes to the desired temperature before startup. It decreases the wear-out and increases the life-time and reliability in startup. Also, the voltage required for ignition is smaller.

Each tube has its own preheating circuity. Tube 1 uses L4. Tube 2 uses L5. The preheating voltage and time is set-up in software and is controlled by the TOP and BOT signals from the HRP.

The flickering effect is caused by reducing the voltage to zero during the light ballast operation. To avoid this, the Zener diodes D4 and D5 maintain a small voltage on both tubes at all times.

The output inductance circuity performs several important functions in the light ballast application. It helps to ignite lamps, when tube parameters differ (due, for example, to different aging of the lamps). It removes the flickering effect and provides filament preheating.

Dimmable Light Ballast with Power Factor Correction, Rev. 1

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Freescale Semiconductor

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Freescale Semiconductor M68HC08 manual Inverter
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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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