A single-stage high-power-factor electronic ballast with auto frequency searching capability provides a compact and efficient solution for ballasting metal halide lamps. The circuit configuration is originated from the integration of a buck-boost converter and a half-bridge resonant inverter. The buck-boost converter is designed to operate in discontinuous current mode (DCM) to improve the input power factor and at the same time to regulate the output lamp power. The resonant inverter operating at a high frequency is adopted to obtain a high efficiency on the power conversion circuit. The control strategy of auto frequency searching is realized by a microprocessor along with the acoustic resonance detection circuit. To avoid the acoustic resonance, an auto-frequency-searching method is used to search ¡§quite windows¡¨ on operating metal halide lamps with the high-frequency electronic ballast. Provided the acoustic resonance should happen to the lamp on operation, the electronic ballast will automatically change the operating frequency until a stable frequency is located. When the operating frequency has been changed, the duty-ratio of the buck-boost converter is adjusted to regulate the lamp power at the rated value. Experimental tests are carried out on a laboratory with 70-W metal halide lamps to verify the effectiveness of the auto-frequency- searching control.

The acoustic resonance phenomena of metal halide lamps are investigated. A measuring system is set up to examine the effects of the acoustic resonance to the shape of the lamp arc, the lighting energy spectrum, the color temperature, the light output as well as electrical characteristics. Two ballast circuits are built to drive the lamps with the sine-wave current and the square-wave current, respectively. One ballast employs the series resonant inverter to output the sinusoidal lamp current. The other makes use of the full-bridge inverter to drive the lamps with the square-wave current. They are operated over a high-frequency range from 20kHz to 30kHz. For both ballast circuits, the operating frequency and the magnitude of the lamp current can be controlled independently. ¡@¡@The experiments are conducted on the 70-W metal halide lamps. The experimental results show that the spectral energy and the color temperature change more significantly as the acoustic resonance becomes more serious. These effects become less significant when the lamps are driven by the square-wave current. The degree of the acoustic resonance can be identified by detecting the variation of the lamp voltage or the output light. The investigated results of the thesis can provide useful information when a standard of the acoustic resonance is considered.

Fluorescent lamps with ac current generate alternating lamp power and thus the light fluctuates at twice the operating frequency. To observe the light fluctuation from a fluorescent lamp, a light detector is built by using high sensitivity phototransistors in this thesis. The test results show that the light output waveform is very similar to that of the lamp power. It is also found that the light output from the whole lamp tube is not identical because the light output fluctuation becomes significant when close to the end of the lamp. When the lamp comes to the life-end, its light output is different from those produced by lamps of good conditions. In attempts to further discuss the features of light fluctuation, an electronic ballast with balanced multi-phase outputs is designed and built to reduce the variation in the light output. With a balanced multi-phase operation, the resultant light output from lamps¡¦ multi-phase currents should be a constant. An experimental 3-phase electronic ballast circuit is built to test this theoretical prediction. Experimental tests confirm that the light fluctuation can be effectively reduced by operating lamps with balanced multi-phase currents.

In this thesis, a novel electronic ballast that includes a repeatedly resonating ignition circuit is proposed for metal halide lamps. The proposed electronic ballast features a two-stage structure that comprises a power factor corrector and a full-bridge inverter used for current control, filtering and ignition. The full-bridge inverter consists of a leg operating at low-frequency with unidirectional switches and a leg operating at high frequency with bidirectional switches. The low-frequency side performs repetitive resonating on the load circuit with inductors and capacitors to accumulate a high voltage for ignition. Adjusting the duty-ratio of the high-frequency side allows for the regulation of the lamp current. The inductors and capacitors in the load circuit function not only producing the high ignition voltage but also filtering out high-frequency components, so that to drive the lamp with a low-frequency square-wave current. The proposed electronic ballast employing the full-bridge inverter with the specially designed control scheme and circuit parameters allows the metal halide lamp to tackle the demanding starting transient and steady state operation. With a simpler circuit structure and a reduced component count, the product cost will be much lower.

Abstract The metal halide lamp is one of high-intensity discharge lamps. It has many advantages such as good color rendering, high efficacy and a variety of color presentations. However, the problems of acoustic resonance, a long transition period of cold starting, and an extremely high ignition voltage for hot restarting should be overcome. The investigation of the thesis is focused on the electrical characteristics of the metal halide lamp operating at high-frequency. Included are the acoustic resonance, starting transient and steady state operation. Various ballast circuits incorporating with ignitors are designed to drive several 70-W metal halide lamps. The operating frequency ranges with acoustic resonance, the ignition voltages for both cold starting and hot restarting, the transition period, the dimming performance, and the lamp equivalent resistance during the lamp life are measured and analyzed. Based on the investigated results, a useful guideline can be provided for the operation and design of the electronic ballast for metal halide lamps. Key words : Metal halide lamp, electronic ballast, acoustic resonance, hot restarting.

A robust design utilizing consecutive orthogonal arrays algorithm is proposed for designing electronic ballasts of fluorescent lamps. By this design method, the variation in the lamp power can be less than 10% under different operating conditions. In the manipulation of the consecutive orthogonal arrays, component values of the ballast circuit and DC-link voltage are used as controllable variables for inner orthogonal arrays; while manufacturers, ambient temperature, used hours, and variation in DC-link voltage are treated as uncontrollable variables for outer orthogonal arrays. The average effects of the output power for each controllable variable are calculated from simulation results, which are served as indexes to find the combination of circuit parameters with a better solution. With consecutive orthogonal arrays, the target values of the circuit parameters are approached step by step. In addition, the effect of the DC-link voltage on the lamp power can be understood from the uncontrollable variable of outer orthogonal arrays. The proposed design tool is implemented on the design of an electronic ballast for a 40W fluorescent lamp. The test results show that the designed electronic ballast can be adopted for the lamps from different manufacturers, with different used hours, and under variation in a wide range of ambient temperature.

Fluorescent lamps are nowadays the most important light sources in industrial, commercial, and domestic applications. To drive fluorescent lamps, electronic ballasts with high-frequency resonant inverter, instead of the electromagnetic ones, are increasingly used due to the benefits of lightweight, small size, high luminous efficiency, and long lamp life. Recently, efforts are concentrated on how to reduce the product cost as well as to improve the circuit performances. To further curtail the product cost, the power-factor-correction circuit is integrated into the ballast circuit as single-stage high-power-factor electronic ballast. On the other hand, the unit cost per lamp can be substantially reduced by developing a ballast circuit which is capable of driving multiple lamps. For convenient use, the user may turn on the desired number of the lamps in accordance with the expected luminosity. A starting-aid circuit is added to eliminate the glow current during preheating. In addition, a protection circuit will be included in the multi-lamp electronic ballast. In case of operating partial lamps, a high power factor at the line input will be always retained. In this thesis, the feasible circuit configuration is developed and design equations are derived. Accordingly, design guidelines for determining circuit parameters are provided. The laboratory circuits are built and tested to verify the computer simulations and analytical predictions.

A new starting profile, instead of ANSI C82.11, is defined to illustrate the starting transient of rapid-start fluorescent lamps driven by high-frequency electronic ballasts. By scrutinizing the lamp voltage and current waveforms, the starting transient can be classified into preheating, glow, and glow-to-arc stages. By the new definition, the starting characteristics of all ballast-lamp circuits can be well interpreted. To investigate the starting performance, a test system is set up. Experimental results show that the time required for glow and glow-to-arc stage is significantly affected by the starting voltage, the filament preheating and the environment temperature. On the basis of the in-depth analysis on the investigated results, the starting characteristics of rapid-start fluorescent lamps are well understood, providing useful information for designing the starting scenario for the ballast.

A high-frequency electronic ballast with auto-tracking control was proposed to operate the metal halide lamps at a specific frequency free from acoustic resonance. In case the acoustic resonance should happen, the operating frequency is changed step by step with the auto-tracking control, until the lamp is operated at a frequency with stable operation. The electrical characteristics of the lamps are first investigated. Based on the investigated results, a detection circuit is designed to identify the occurrence of acoustic resonance. With the auto-tracking control, the Class-D half-bridge series-resonant inverter can be adopted for the high-frequency electronic ballast to achieve high efficiency and high power density. The control strategy of auto-tracking is practically realized by a single-chip microprocessor. The proposed approach is implemented on a 70 W test lamp with an operating frequency range from 20 kHz to 30 kHz. To regulate the lamp power at its rated value, a buck-boost converter is used as a pre-regulator, which serves also as a power-factor-corrector to achieve a high power factor at the input line.

In this thesis, a high voltage discharging testing circuit is proposed for cold cathode fluorescent lamps(CCFLs). The testing circuit uses only a single active power switch operating at a high frequency incorporating with reactive components to accumulate a relatively high voltage on the capacitor. This voltage is then stepped up by a transformer to provide the required high voltage for discharging the CCFLs. The circuit has the advantages of simple configuration, less component count, and low cost. In addition, a high power factor at the ac line source can be achieved. The proposed circuit is analyzed based on the mode operation. Accordingly, the design equations are derived to determine the circuit parameters. A prototype is designed and built for testing the 19 inch CCFLs. The discharging tests are made to recognize the malfunctions during the manufacturing process. Moreover, the distributions on the spectral power and chromaticity of lamps can be examined to ensure the product quality.