11 - Tripping the Light Fantastic

The fine-tube cold cathode fluorescent lamp (CCFL) [1-2] and external electrode fluorescent lamp (EEFL) [3-9], have been widely used as a backlight source in liquid crystal display (LCD) modules. In a notebook PC, the glass tube diameter of the lamp is a small as 1 mm. As the display area becomes larger in LCD TVs, the tube diameter is 3~4 mm and the lamp length is up to 1~2 m. However, the mechanism for radiation of light along such a long positive column is not well understood. The characteristics of light emission in the EEFLs have been reported, specifically the propagation of a light-emitting along a tube driven by high voltage AC [8-9]. In the long positive column lamp, the light emits first from the side of high voltage propagates to the ground side with the propagation time of ~┤s and the propagation velocity of 105~106 m/s. The previous observations have not been reported elsewhere to our knowledge since the fluorescent lamps have been introduced commercially in the 1940's. However, those observations of light propagation would not be recognized even if they have been found first in the history of fluorescent lamps. Even more, those observations are misapprehended as the kinds of unstable waves during the lamp operation of lamp, such as striation, snaking, flickering, and streaming, etc. Generally, a moving light source in the long positive column plasma has been associated with “striation”. A striation is a quasistanding wave which can be observed visually [1012]. However, striations as well as the other unstable waves are not observed in commercial lamps, and would be considered a major defect for hot cathode fluorescent tubes as well as CCFL. In the manufacture of those lamps, inadequate vacuum during the evacuation process results in impurity gases such as H2O, CO2, O2, and N2, etc. These impurities cause the perturbations of unstable discharge, and those lamps are discarded in the production line. Striations can sometimes appear in aging lamps or in the operation with an unstable inverter system. However, we have never observed striations in the normally manufactured lamps of our test samples. Our observation of optical signal is quite different from striations, as it is not visible to the naked eye and moves on the micro-second timescale. Rather than the instability, they are related to the stable process of distribution of plasma and fields that generate light in these discharges.

This work presents a multiphase multilamp driving system for liquid crystal display (LCD) back light The driving system adopts a multiphase inverter to drive cold cathode fluorescent lamps (CCFL) to reduce input current ripple. Furthermore, to prevent current imbalance among lamps a multiphase transformer is introduced in the proposed system. Compared with the conventional single-phase driving system, the proposed one can have the merit of requiring less number of transformers. A three-phase driving system with current balancing transformer has been built, from which experimental results have verified the feasibility of the proposed multiphases driving system.

This paper proposes high performance control of light emitting diode(LED) drive system for liquid crystal display(LCD) backlight. The CCFL(cold cathode fluorescent lamp)was used to a conventional LCD backlight. Due to improvement on luminous efficiency, long life and wide color gamut, LED has gradually substituted for CCFL as backlight. The backlight using LED is necessary to use many LED. For that reason, the LED backlight is using a lot of LED driving circuits. The many LED driving circuit is generated a current deviation between LED. Eventually, it is caused brightness deviation between LED. Therefore, this paper improves the current deviation using transformer and balancing capacitor to solve this problem. Also, for accurate and uniform brightnesss control, this paper is applied the artificial intelligent control to a dimming control. This paper is compared with conventional system, and validity of this paper proves through that result.

Parasitic capacitors, which occur between cold cathode fluorescent lamps (CCFLs) and the back-plank in backlight modules of liquid crystal display (LCD) panels, are changed by the lamp position. That's the reason why the leakage currents are different from lamps; therefore, the undesirable non-uniform brightness exists. This paper presents a novel structure of backlight module for LCDs, aiming at alleviating the influence of parasitic capacitors in order to attain balanced lamp currents and uniform brightness outputs. By designing a new back-plank, the spaces between the lamps and the back-plank are approximately identical, as a new structure implemented on a direct-type backlight module with 14 CCFL lamps for a 32-inch LCD panel, then experimental results demonstrate that the difference of parasitic capacitors can be reduced to be within 2 %.

Chapter 5 - Performance Characteristics

We developed two mobile-device size autostereoscopic integral videography (IV) displays with field sequential color (FSC) liquid crystal displays (LCDs) and micro lens arrays. IV is an autostereoscopic video technique based on integral photography. The FSC-LCD has a different backlight from that of conventional LCDs. The backlight is produced by red, blue, and green light emitting diodes (LED) instead of by cold cathode fluorescent lamps, and each LED emits light sequentially. IV based on FSC-LCD doesn't cause color moires because the FSC-LCD does not require color filters. One FSC-LCD IV display is 5-inch diagonal with 256×192 lenses and 20 ray directions. Its base FSC-LCD is 300ppi with 1280×768 pixels. The other FSC-LCD IV display is 4.5-inch diagonal with 192×150 lenses and 80 ray directions. Its base FSC-LCD is 498ppi with 1920×1200 pixels. In this paper, we first describe the problems of a previous conventional LCD-based IV displays, and then describe the principle of the IV displays based on the FSC-LCDs. Next, we analyze the IV displays by a plenoptic sampling theory. Lastly, we compare three versions of the IV displays, two based on the FSC-LCDs and one based on the conventional LCD.

One potential application of cold cathodes is flat panel displays. At present, the market for emissive displays is based on cathode ray tubes (CRTs) and liquid crystal displays (LCDs). However, these technologies do not offer the combination of bright, sharp images in a low power, lightweight and flat package. Cold cathodes should offer these advantages in the not-too-distant future. Since the international market for displays by the year 2000 is predicted to reach over $20 billion (US), an increasing number of innovative cold cathode concepts should be expected.

The color characteristics of medical liquid-crystal displays (LCDs) have become one of the main interests in quality assurance and quality control of medical display devices. It is necessary to evaluate variations of the color characteristics in medical LCDs in order to provide consistent color characteristics for image reading. In this study, we characterize the color characteristics in grayscale images displayed on medical LCDs. Eight medical color LCDs and eight medical monochrome LCDs were used in this study with operating times ranging from 800 to 25 000 h. Default settings of correlated color temperature (CCT) of white points for all color LCDs were set at 7500 K. We measured chromaticity in the Commission Internationale de l'Éclairage (CIE) u'v' color space and CCT of the white point at 18 luminance levels. A colorimeter and grayscale test patterns with various luminance levels were used for the measurements. First, we examined differences in chromaticity and CCT at 18 luminance levels for each LCD. Second, we compared chromaticities of the different LCDs. Then, chromaticity and CCT of LCDs were measured at different ambient light conditions (30 and 560 lux) and compared to those measured in a dark room. Finally, the relationship between operating times and CCT was evaluated. The chromaticities of monochrome LCDs changed toward the blue and CCT increased as luminance decreased. In color LCDs, the chromaticity and CCT of the white point except at the minimum luminance were nearly constant to those measured at the maximum luminance. We observed differences in chromaticity between color and monochrome LCDs because of the nonadjustable white point of monochrome LCDs. When the ambient light increased, chromaticity varied, and CCT decreased on every LCD. Ambient light had a much greater impact on chromaticity and CCT at lower luminance levels. The CCT of LCDs decreased in longer operating times. The grayscale of LCDs with longer operating times was measured to be more yellowish due to the degradation of cold cathode fluorescent lamps. Our results clearly indicate that the white point in grayscale images displayed on medical LCDs changes depending on luminance levels, color or monochrome LCDs, ambient light conditions, and operating times. These data provide useful information to understand color characteristics of LCD for image reading, especially for quality assurance and quality control of LCDs.

Backlight unit (BLU) is one of essential components constituting liquid crystal display (LCD). It can be fabricated with several different methods. Cold cathode fluorescent lamp (CCFL) can be made with a low cost process and has high quality of color reproducibility. But it cannot provide a high quality of brightness & contrast and can raise environmental issue since Hg is used as a law material. White light-emitting diode (WLED) has long lifetime and dynamic control feature, but it has complicated structure and needs high fabrication cost. Meanwhile, carbon nanotube based BLU (CNT-BLU) enables local dimming and impulse & scan driving, and can accomplish best quality of moving pictures by maximizing brightness & contrast functions. However, high fabrication cost is a large barrier for commercialization. In this study, we applied low-cost electroless deposition process of the metallization comprising CNT-BLU substrate. Current fabrication processes of CNT-BLU go through several times of photo patterning and firing of CNT paste, which results in complicated and high-cost processes. Metallization of backlight unit can be made either with Cr (Mo) patterning using conventional photo process or with stencil printing of Ag paste. The former uses vacuum processes using expensive semiconductor equipments such as sputter and evaporator, and the latter uses expensive law material like Ag. BLU substrates are formed by firing and activating the CNT pastes which was printed on the metallizations. Fabrication of BLU substrate can be simplified with electroless deposition method and the cost can also be much lowered. In the present study, feasibility of electroless metallization on the CNT-BLU substrate was tested. Glass substrate was pretreated with base solution and then etched with buffered oxide etch (BOE) solution, followed by seeding process by alternating dipping the substrate in Sn and Pd solution in turn. Electroless Ni(P) deposition was conducted on the substrate using a commercial Ni(P) bath with varying P content (4–9wt%). Adhesion test was conducted with as-plated and fired specimens. The Ni(P) film with low P content showed better adhesion performance than those with high P content. Electrical conductivity was also high in the low P containing specimens. Sheet resistances of them, measured by four point probe, were several ohm/sq and it decreased one order of magnitude lower after firing at 460°C. Decrease of resistance results from phase transformation of metastable Ni(P) film into stable Ni & Ni <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> P phase. Surface roughness of the substrate was ∼90nm after BOE etching and ∼200nm after Ni(P) deposition with 2µm thickness.

In this paper, a bi-frequency control based zero-voltage-switching push-pull driver with a wide dimming range is proposed for the cold cathode fluorescent lamp (CCFL) based back lighting of the liquid crystal display (LCD). As a result, not only the design of the driver transformer can be simplified but also the efficiency of CCFL can be improved. Finally, a prototype is constructed for verifying the effectiveness of the proposed LCD driver.

Color gamut and static and dynamic color shifts of a multi-domain in-plane-switching liquid crystal display (IPS LCD) are calculated quantitatively using RGB (red, green, and blue) light-emitting diodes (LEDs) and cold-cathode fluorescent lamp (CCFL) backlights. Simulation results indicate that the LED backlight exhibits a wider color gamut, better angular color uniformity, and 2-4X smaller static and dynamic color shifts than the CCFL system.

The substation of the power system supplies electricity to industrial plants as the primary source. The high-voltage electrical equipment is essential to maintain the stable operation of the substation. Therefore, the periodic inspection of high-voltage electrical equipment is essential in small factories as well as in large industrial plants. The high-voltage transformer, as one of the equipment, is required in the substation with power cables, bus bars, and high-voltage isolation switches and circuit breakers as related peripherals. At present, the inspection circuit is connected directly and simply to the high-voltage circuit breaker, which is dangerous for inspecting engineers. To remove the risk of the inspection of high-voltage circuit breakers, we developed an "AC/DC auxiliary detection module" to improve safety and convenience. The output voltage switching function is added according to the different voltage requirements for AC and DC controls. Through the detection module, the inspector monitors AC or DC voltage output according to the voltage demand of the high-voltage circuit breaker. When the voltage is overloaded in the input terminal, a protection mechanism initiates to prevent the fault of the equipment and ensure the safety of the inspectors. The inspection device cut the power off to protect the equipment under high current or continuous abnormal output voltage. Accidental touch of the output terminal of the auxiliary detection module in the equipment shell and other parts automatically cut the power off, too. The developed module provides the safety for the subsequent inspections of high-voltage circuit breakers.

Thermal effects were investigated in a liquid crystal display (LCD) backlight unit (BLU) that was composed of light emitting diode (LED) arrays. The driving power for a single LED in a BLU is determined by the desired brightness of the LCD panel and the pitch distance between adjacent LEDs. As the pitch distance increases, individual LEDs need to be driven by a higher power in order to maintain the same brightness. Since the junction temperature of an LED plays an important role in LED performance, such as optical efficiency, intensity degradation, and lifetime, the maximum driving power for an LED should be limited by a critical level of the junction temperature. A guideline for designing LED BLU panels taking account of the junction temperature is presented using various parameters of LED arrays.

Although microwave induced plasmas are well known as high efficiency plasma sources, their uses in laboratories are limited since the microwave power systems are complicated and expensive. The output power of commercially available low-cost microwave ovens is fixed and discontinuous resulting from the high voltage doubler topology of the magnetron tube power supply. In this paper, a high voltage switched mode power supply of forward topology has been developed for continuous microwave power radiation. The forward converter can generate a no-load high voltage output maximum of 7 kV. When driving the magnetron tube, the microwave output power could be varied from 0 to 35 W while the high voltage output level was constantly regulated at -3.4 kV. A microwave induced plasma system was setup to investigate the plasma produced. A low pressure argon plasma was produced with only 2 W over a wide range of pressures.

High voltage generally means electrical energy of higher magnitude sufficient to inflict human beings. So, safety requirements and particulars are to be followed while designing the model. The objective of this paper is generation of high DC output voltage from two methods, namely flyback converter and Cockcroft–Walton voltage multiplier with input DC supply. Mathematical modeling, control strategy, circuit operation, and design considerations are discussed. High-voltage power supply for a particular application has become cheaper due to latest advance in power supply technology. Many applications are of high DC supply in industry, research work, dielectric testing of high-voltage equipment.