An efficient self-configurable driver for color light emitting diode

To arrange an accurate load current for the different sets of color LEDs, an efficient LED driver must facilitate the current sharing among the LED strings using a constant current source. Effective utilization of power in an LED string is vital for display panels as it defines the magnitude of the undesirable phenomenon of flickering switching. An efficient and dimmable LED driver suitable for LED back-light drivers in the LED display panel is presented in this thesis. This thesis proposed a color LEDs driver with a self-configuration of the enhanced current mirror in multiple LED strings. In this proposed work, the load currents have been efficiently balanced among the identical and unequal loads of color LEDs. In a traditional current mirror, the buck converter is linked with a fixed current load. Nonetheless, in the proposed improved self-adjustable current mirror, the variation of LEDs load string could be addressed using a single buck converter. The improvement is based on the combinational circuits of transistor and op-amp with proper scheme biasing. The improved dimming circuit is then proposed for exploiting the range of dimming at the string and module level. Furthermore, the proposed current-balancing circuits excluded a separate power supply to control current in different load strings of LEDs (red/green/blue). Since the approach circuit is identical and modular, it could be scaled to any number of parallel current sources. The different bi-level pulsating driving have been performed to reduce the loss while running the LEDs at the high peak current. It is to create two driving parameters, which are the low/high current levels (pulse width modulation) and associated duty cycles, in having the capability to control luminosity effectively. It can be seen, the previous techniques had improved the luminous efficacy of LEDs by using n-level driving techniques but at the trade-off of losing efficiency with the introduction of resistors (variables in series) to create a bi-level phenomenon for the driver. Therefore, this thesis proposes to replace the resistors with the new approach dimming circuit to get a significant improvement in the overall system’s efficiency that can assist to dim an individual LEDs string based on designated color (red or green or blue) LEDs. Meanwhile, in improving illuminance through dimming, the hybridization of pulse width modulated (PWM) and amplitude modulated (AM) has been proposed. As a result, the proposed LEDs driver has shown effective current balancing through the color LEDs string with exploiting a large dimming range. The illumination analysis has also shown a significantly higher when compared with PWM (bi-level pulsating). The computation efficiency for red, green, and blue LEDs strings around range 92% to 99%

Precise Color Control of Red-Green-Blue Light-Emitting Diode Systems

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New Horizons in Ocular Surface and Dry Eye Evaluation

Although considered to be the most important of all the human senses, the delicate nature of the human eye gives rise to many potential defects that could impact the quality of sight and if left untreated eventually lead to permanent vision loss. Scientists and engineers have studied human vision with a desire to better understand and diagnose conditions that may compromise sight. With the never-ending advancement of technology, new avenues of exploration are continually becoming available which can offer the potential for reduced invasiveness whilst extracting even greater diagnosis fidelity. Nevertheless, even with new technological possibilities, many potential solutions are not suited to day to day clinical environments and may be cost prohibitive or simply unreasonably complex to perform. In many cases subjective observation techniques introduced over a century ago still find favour today and may be preferred over newer methods due to large accessibility and low training requirements. This thesis is an exploration of cutting-edge technical approaches and developments with the intention of applying them in an original yet rational fashion to achieve mainstream use in real day to day clinical settings for the provision of superior dry eye diagnosis capabilities. The following research will be focused on identifying anterior eye conditions, in particular dry eye which is growing in prevalence and affecting younger age groups. Rather than restricted, in depth focus on a particular technique, this work will consider several unique approaches and lay a strong argument for their viability and subsequent clinical testing in separate, future work. Chapter 2 focuses on improving the commonly used technique of sodium fluorescein viewing with custom created blue excitation and yellow emission filters. Although such subjective fluorescein observation techniques have existed for many years, the custom filters offer a large improvement in viewing performance, filter efficiency and slit lamp hands free usage, and are ready to scale to production with 1,000 units already manufactured and a further 16,000 units on order. Chapter 3 describes research on determining the thickness and degradation of the transparent tear film over the course of a blinking cycle. To date, many attempted measures have produced results with an accepted value in the region of 5 μm. Tear dynamics; refresh, spreading and degradation behaviours are key in providing insight into the stability and premature breakdown leading to dry eye disease, all of which are demonstrated as possible with confocal and interferometric technologies being examined and an average tear film thickness value 3.28 μm and degradation rate of 0.048 ± 0.034 μm-2 being achieved. Lastly, chapter 4 introduces a new anterior eye assessment instrument based on the technique of persistence of vision that is capable of enhancing the ability to detect tear film break up time in a new low cost, non- invasive device. A plethora of additional anterior eye examinations such as corneal topography and slit lamp viewing capabilities are also made possible with this new projection method. The POV scope is a distinctive new approach to anterior eye viewing and gives the ability to capture high resolution, high contrast images that in the near future may be coupled to a machine learning platform to provide a clear diagnosis for common conditions including the multifactorial and inconsistent signs and symptoms of dry eye disease