In the thesis, a LED driver circuit that is applied in low power LED lighting with constant output current and Power Factor Correction (PFC) is presented. For power stage of LED driver, a non-insulated switching Buck power converter without transformer is used, and develop equivalent mathematical model and block diagram of Buck converter while its inductor current operating in Continuous Conduction Mode(CCM). Furthermore, the closed loop PFC control circuit is designed by time-domain and frequency-domain analysis. In addition, because of the classical PFC control configuration needs the expensive multiplier, a LED driver circuit with PFC without multiplier is presented in this thesis in order to reduce the system cost and space of the circuit. Then, we confirm the designed circuit by simulation and experiment. By the results, the proposed system achieves constant output current control and power factor can reach to 0.92.

In the thesis, an LED driver circuit with Power Factor Correction (PFC) and constant output current is presented. For open-loop LED driver, an insulated switching Flyback power converter is designed, and the Flyback converter will be operated in Continuous Conduction Mode(CCM). One develops equivalent mathematical model for the drivers system. The main part of this thesis is about the design and the study of a closed loop PFC control circuit using inductor voltage sensing technology. In addition, one introduces another traditional inductor current sensing control technique is included to compare with the designed control circuit. Then, one confirms the designed circuits by simulation and the experiment. From the results, the power factor can reach to 0.97, and the expected constant output current control has also been achieved.

Nowadays, using the LED as backlight module's light source becomes generalization gradually, and the application of LED light source develops from the liquid crystal display to the liquid crystal TV. However, thermal dissipative problem of LED component is still an important issue to study presently, since it can affect the service lives of LED and LCD seriously. In order to increase the luminous energy of the LED component, one need to increase the supply of electric power and it will cause the increment of thermal dissipative problem of the LED component also. Therefore, by considering the LED components as the light source of the backlight module , the purpose of this study is to reduce number of the required LED components in order to decrease the thermal dissipative problem of LEDs, and maintain the luminous and uniformity of the backlight module simultaneously. A new packaging for LED, named SMD type metallic reflection cup LED component, was proposed in this study. The new LED package not only has a better thermal dissipative property, but also can control its radiation property by changing the angle of its reflection cup. So, the proposed LED package can be applied for different purposes. By applying the proposed LED components as the light source of a backlight module, under the condition of same illumination, it can be shown that the required number of LED components can be decreased tremendously and so the thermal dissipative problem can be decreased too. Also, the numerical simulated results showed that by choosing the suitable angle of the reflection cup, the uniformity of the backlight module can be improved. Besides, this study proposed a modified method for assessing the uniformity of a backlight module. The simulated results showed that the proposed method can assess the uniformity of a backlight module more suitable than the traditional nine points measurement method can do.

As we enter into a high energy consumption era, people start taking notice of a simple electronic device called Light Emitting Diode (LED). A continuous rise of crude oil price in global markets and the proposal of WEEE and RoHS by European Union, ¡§energy efficient¡¨ and ¡§environmental friendly¡¨ are becoming more and more important, which leads to the attention of LED. It¡¦s one of the so called ¡§green¡¨ light emitting sources and will be the market¡¦s mainstream in near future. Therefore, LED will become another star product after the measurement of the IC and TFT-LCD industries. Taiwan has been developing LED for over 30 years and has developed a well rounded market structure. Facing huge demand by application such as computer monitor backlight, car lighting, and daily lighting appliance, Taiwanese LED supplier already responded by adjusting their market strategy and increasing their product quality. Many companies began to involve the upstream epitaxial techniques and products. How to survive through well-down strategy development is a key for these upstream suppliers. The purpose of this study is to understand how a new company to build competitive advantage through the case study of the U company. When the U company was found, it uses a different production mode to overcome many problems from traditional production modes. The U company¡¦s strategies lets it could develop fast, provide stable quality products, and manufacture with lost cost. Through this case study, this study wants to shed some light to other people who have interests in the LED industry.

This thesis is to design an LED driver circuit with constant output current and Power Factor Correction(PFC) control. Switching power converter is applied for power stage of the LED driver circuit, a non-insulated Buck converter without transformer is used, and the inductor current of Buck converter is operating in Continuous Conduction Mode(CCM). According to the operating principle of Buck converter, the equivalent mathematical model and system block diagram is developed to establish the traditional closed loop PFC control circuit. The controller parameters are set up by time-domain and frequency-domain analysis to achieve the goal with constant output current and PFC control. Furthermore, the thesis presents a more effective PFC control method to reduce the cost of multiplier used in traditional PFC control method and overcome the congenital defect of Buck converter. Both two PFC control methods are confirmed and compared by simulation and experiment. The results show that the proposed control method has more effective performance and achieve constant output current for LED with high power factor by 0.966 under full-load condition.

Thesis (Ed.D.) -- Central Connecticut State University, 2009. / Dissertation advisor: Karen Beyard. In partial fulfillment of the requirements for the degree of Doctor of Education. Includes bibliographical references (leaves 129-136). Abstract and full text available via the World Wide Web.

Trivalent rare earth cations (RE3+) activated nanometre-sized Y2O2S and Gd2O2S phosphors were prepared by converting hydroxycarbonate precursor powders during a firing process. The precursors were prepared using the urea homoprecipitation method. The choice of host crystal and dopant were optimised to meet the specific requirements for practical applications in the field of lighting, X-ray detection, and displays. Parameters that affect the luminescent properties of the resulting phosphors, such as doping concentration, excitation mechanism, firing temperature, and host lattice were investigated. Tb3+ and Er3+ co-doped Y2O2S and Gd2O2S were studied for their upconversion properties under 632.8 nm red laser excitation. The intensities of UC emission were affected by both doping concentration and host lattices. Tb3+ and Er3+ co-doped Y2O2S was found to show strong downconversion from Tb3+ and upconversion from Er3+. The presence of the Er3+ cations directly affects the Tb3+ down-converting properties by acting as centres for energy transfer. The possible energy transfer between Gd3+ and Er3+ should be responsible for the different trend of Er3+ upconversion intensity in Y2O2S and Gd2O2S. It has been established that the Tb3+ and Er3+ co-doped system is superior than the Yb3+ and Er3+ co-doped one. In the latter system the presence of Yb3+ reduces the efficiency of both upconversion and downconversion emission under red laser excitation. These phosphors show potential applications in the security and anti-fraud field. The novel ZnS:Mn QDs were prepared and successfully incorporated into GaN based photonic crystal (PC) holes to efficiently produce white light. The crystal structure and luminescent properties of the ZnS:Mn QDs were investigated as well as the factors affecting the filling rate. Zn1-xCdxS:Mn QDs were also investigated. The addition of Cd cations leads to a red shift in the PL excitation spectra of the Zn1-xCdxS:Mn QDs. The crystal structures and surface properties were also affected by the presence of Cd. Monodisperse PbS QDs with particle size of ~5 nm has been obtained using a similar aqueous reaction method.

The modern society relies heavily on mankind’s ability to produce light to lengthen the day. Throughout the evolution of artificial lighting lots of light sources were discovered / invented, i.e. burning wood, oil, candles, using incandescent bulbs and fluorescent lamps and, finally, white LEDs. LEDs are superior to other light sources due to their high efficiency. Replacement of conventional light sources by white LEDs what would allow saving huge amounts of electricity consumed for lighting purposes. The main goal of this dissertation was development and investigation of various new materials that could be used in solid state light sources based on near-UV and blue LEDs. One silicate, one molybdate and three garnet structure compounds were selected. Several synthesis methods, i.e. solid state, sol-gel, and sol-gel combustion, were applied in preparation of selected host materials. The host materials were activated by Eu2+, Eu3+, and Ce3+ ions. The phase purity of synthesized samples was evaluated by recording powder XRD patterns. Luminescent properties of the activator ions were investigated by recording reflectance, excitation, emission spectra and decay curves at room temperature. The temperature dependent decay curves and emission spectra were recorded in the range of 77-500 K. Moreover, quantum yields, luminous efficacies and colour points were calculated from the obtained data. / Žmonija jau nuo senų senovės stengiasi prailginti dieną dirbtiniais šviesos šaltiniais. Šviesos šaltiniai vystėsi pamažu – iš pradžių buvo deginama mediena, žibalas ir žvakės, vėliau buvo išrasta kaitrinė lemputė, o dar po kurio laiko fluorescencinė lempa. Jauniausi iš dirbtinių šviesos šaltinių yra šviestukai, kurie yra pranašesni už prieš tai minėtus šaltinius savo dideliu efektyvumu. Pakeitus dabartinius šviesos šaltinius šviestukais, būtų galima sutaupyti milžinišką elektros energijos kiekį, suvartojamą apšvietimui. Pagrindinis disertacijos tikslas buvo buvo naujų liuminescencinių medžiagų, kurios gali būti sužadinamos ultravioletinę arba mėlyną spinduliuotę emituojančiais šviestukais, paieška. Iš viso pasirinktos penkios sistemos – vienas silikatas, vienas molibdatas ir trys granato struktūros junginiai. Medžiagos buvo susintetintos kietafazių reakcijų, zolių-gelių arba zolių-gelių užsiliepsnojimo metodais. Junginiai buvo legiruoti Eu2+, Eu3+ arba Ce3+ jonais. Fazinis junginių grynumas buvo patvirtintas Rentgeno spindulių difrakcijos analize. Junginių optinės savybės buvo įvertintos išmatavus atspindžio, sužadinimo ir emisijos spektrus bei liuminescencijos gesimo trukmes kambario temperatūroje. Taip pat buvo įvertinta junginių liuminescencijos gesimo trukmių ir emisijos spektrų priklausomybė nuo temperatūros, bei apskaičiuoti kvantiniai našumai ir spalviniai taškai.

Žmonija jau nuo senų senovės stengiasi prailginti dieną dirbtiniais šviesos šaltiniais. Šviesos šaltiniai vystėsi pamažu – iš pradžių buvo deginama mediena, žibalas ir žvakės, vėliau buvo išrasta kaitrinė lemputė, o dar po kurio laiko fluorescencinė lempa. Jauniausi iš dirbtinių šviesos šaltinių yra šviestukai, kurie yra pranašesni už prieš tai minėtus šaltinius savo dideliu efektyvumu. Pakeitus dabartinius šviesos šaltinius šviestukais, būtų galima sutaupyti milžinišką elektros energijos kiekį, suvartojamą apšvietimui. Pagrindinis disertacijos tikslas buvo buvo naujų liuminescencinių medžiagų, kurios gali būti sužadinamos ultravioletinę arba mėlyną spinduliuotę emituojančiais šviestukais, paieška. Iš viso pasirinktos penkios sistemos – vienas silikatas, vienas molibdatas ir trys granato struktūros junginiai. Medžiagos buvo susintetintos kietafazių reakcijų, zolių-gelių arba zolių-gelių užsiliepsnojimo metodais. Junginiai buvo legiruoti Eu2+, Eu3+ arba Ce3+ jonais. Fazinis junginių grynumas buvo patvirtintas Rentgeno spindulių difrakcijos analize. Junginių optinės savybės buvo įvertintos išmatavus atspindžio, sužadinimo ir emisijos spektrus bei liuminescencijos gesimo trukmes kambario temperatūroje. Taip pat buvo įvertinta junginių liuminescencijos gesimo trukmių ir emisijos spektrų priklausomybė nuo temperatūros, bei apskaičiuoti kvantiniai našumai ir spalviniai taškai. / The modern society relies heavily on mankind’s ability to produce light to lengthen the day. Throughout the evolution of artificial lighting lots of light sources were discovered / invented, i.e. burning wood, oil, candles, using incandescent bulbs and fluorescent lamps and, finally, white LEDs. LEDs are superior to other light sources due to their high efficiency. Replacement of conventional light sources by white LEDs what would allow saving huge amounts of electricity consumed for lighting purposes. The main goal of this dissertation was development and investigation of various new materials that could be used in solid state light sources based on near-UV and blue LEDs. One silicate, one molybdate and three garnet structure compounds were selected. Several synthesis methods, i.e. solid state, sol-gel, and sol-gel combustion, were applied in preparation of selected host materials. The host materials were activated by Eu2+, Eu3+, and Ce3+ ions. The phase purity of synthesized samples was evaluated by recording powder XRD patterns. Luminescent properties of the activator ions were investigated by recording reflectance, excitation, emission spectra and decay curves at room temperature. The temperature dependent decay curves and emission spectra were recorded in the range of 77-500 K. Moreover, quantum yields, luminous efficacies and colour points were calculated from the obtained data.

This practice-led, project-based research charts, simultaneously, my disenchantment and re-engagement with graphic design. By it's dissemination I hope to articulate: 1. How an evolving understanding of my sense disenchantment emerged from the research, and enabled the process of re-engagement. 2. The role, and importance, of provocation and doubt in creative practice generally, but specifically in practice-led research. The difficulty of provoking one's self, and the strategies through which I have tried to enact a disruptive reframing of my practice. 3. That through the highly reflective nature of practice-led research and the greater sense of self-awareness that inevitable comes from that I have been able to re-engage with graphic design. That this re-engagement has, for me specifically, had much to do with my ability to begin to negotiate my own personal terms of reference, so as to be able to locate myself within a community of practice, and to begin to take part in a discourse that has a certain resonance for me. Central to this research are questions about professional practice, dislocation/disinterest, research, resonance and reinvention. As disenchantment is common, perhaps pervasive, within professional practice, my account of this research will propose that a more general understanding of practice-led research-highly reflective, self-initiated work-is essential if graphic design is to support and sustain imaginative, innovative, and inventive practitioners. Rather than target graphic design's inability to support provocative practices (the studio, or the industry), my research focuses on the potential of the individual practitioner to motivate and design a more generative and engaged practice. As such any observations and/or discoveries are not presented as quantitative 'findings', but should be seen rather as generative understandings that promote future possibility and potential for the practice.