A Low-Cost Method for Minimizing the Chromaticity Shift of DC-Driven Phosphor-Converted White LEDs by Thermal Design

K. H. Loo,Y. M. Lai,Chi K. Tse 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

Most commercial white LEDs are made from blue LEDs coated with YAG phosphor. They generally produce emission spectra that shift in opposite directions under the influences of current amplitude and junction temperature changes. By using a commercial white LED sample, LUXEON K2, the effects of current amplitude and junction temperature on the chromaticity shift of white LEDs over dimming, during which both parameters are known to assert their influences simultaneously, are studied experimentally. The impact of driving/dimming by dc current is discussed through a graphical analysis and verified by experimental measurement. Due to the counteracting influences of current amplitude and junction temperature changes, driving/dimming white LEDs by dc current offers a more superior chromaticity stability compared to PWM. By means of selection of a heat sink’s thermal resistance estimated from an analytical equation derived in this paper, it is found that the overall chromaticity shift of white LEDs over dimming can be minimized at low cost.

Development of a Maximum-Power-Point Tracking Algorithm for Direct Methanol Fuel Cell and Its Realization in a Fuel Cell/Supercapacitor Hybrid Energy System

K. H. Loo,G. R. Zhu,Y. M. Lai,Chi K. Tse 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

Direct methanol fuel cells (DMFC) have been widely researched for applications in portable electronics due to their use of liquid fuel for easy storage and transportation compared to gaseous hydrogen. However, DMFC’s performance is strongly affected by methanol crossover that significantly degrades the fuel conversion efficiency at low output power, and is characterized by an increasing efficiency at increasing output power. The maximum efficiency point (MEP) is inherently difficult to track due to the commonly unknown methanol crossover rate, but since it is typically located very close to the maximum power point (MPP), an alternative tracking approach based on the MPP is proposed. In this paper, a fuel-cell-oriented MPP tracking (MPPT) algorithm based on resistance matching is developed, implemented, and tested in the context of a DMFC/supercapacitor hybrid power system. To account for the generally slow fuel cell dynamics, the DMFC is constantly tracked at the MPP while any surplus or deficit power is absorbed or delivered by the supercapacitor bank. The detailed formulation of the algorithm and the power flow design and realization are also discussed.

Variable Bi-Level Phase-Shifted Driving Method for High-Power RGB LED Lamps

S. K. Ng,K. H. Loo,Y. M. Lai,K. T. Mok,Chi K. Tse 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

Based on the recently proposed bi-level driving method, this paper presents an extended version of the existing method, which is aimed at maximizing the luminous output of high-power LED lamps by piecewise-linear tracing of their luminous output curves under AM (amplitude modulation) driving. The proposed driving method divides the luminous output curve of an AM-driven LED into a multiple sections, where each section is approximated by a straight line with two predefined end-points acting as the lower and upper current levels as used in the existing bi-level driving method. The intermediate current and luminosity values lying between the upper and lower current levels are obtained by duty cycle mixing of the two current levels. The joined multiple sections has enabled a near-maximum luminous output to be extracted from the LED while a linear dimming is realized within each section. The proposed driving method is verified by implementation in a single-driver RGB color LED lighting system with the red, green, and blue LED driven in a time-sequential manner (or shifted in phase). Experimental results show that a significant gain in luminous efficacy, hence energy saving, is achieved compared to the commonly used pulse-width modulation (PWM) driving.

Effects of Imperfect Sinusoidal Input Currents on the Performance of a Boost PFC Pre-Regulator

Martin K. H. Cheung,Martin H. L. Chow,Y. M. Lai,K. H. Loo 전력전자학회 2012 JOURNAL OF POWER ELECTRONICS Vol.12 No.5

This paper investigates the effects of applying different input current waveshapes on the performance of a continuous-conduction-mode (CCM) power-factor-correction (PFC) boost pre-regulator. It is found that the output voltage ripple of the pre-regulator can be reduced if the input current is modified to include controlled amount of higher order harmonics. This finding allows us to balance the performance of output regulation and the harmonic current emission when coming to the design of the pre-regulator. An experimental PFC boost pre-regulator prototype is constructed to verify the analysis and show the benefit of the pre-regulator operating with input current containing higher order harmonics.

Effects of Imperfect Sinusoidal Input Currents on the Performance of a Boost PFC Pre-Regulator

Cheung, Martin K.H.,Chow, Martin H.L.,Lai, Y.M.,Loo, K.H. The Korean Institute of Power Electronics 2012 JOURNAL OF POWER ELECTRONICS Vol.12 No.5

This paper investigates the effects of applying different input current waveshapes on the performance of a continuous-conduction-mode (CCM) power-factor-correction (PFC) boost pre-regulator. It is found that the output voltage ripple of the pre-regulator can be reduced if the input current is modified to include controlled amount of higher order harmonics. This finding allows us to balance the performance of output regulation and the harmonic current emission when coming to the design of the pre-regulator. An experimental PFC boost pre-regulator prototype is constructed to verify the analysis and show the benefit of the pre-regulator operating with input current containing higher order harmonics.

Mammalian Systems Biotechnology Reveals Global Cellular Adaptations in a Recombinant CHO Cell Line

Yusufi, F.N.K.,Lakshmanan, M.,Ho, Y.S.,Loo, B.L.W.,Ariyaratne, P.,Yang, Y.,Ng, S.K.,Tan, T.R.M.,Yeo, H.C.,Lim, H.L.,Ng, S.W.,Hiu, A.P.,Chow, C.P.,Wan, C.,Chen, S.,Teo, G.,Song, G.,Chin, J.X.,Ruan, X. Cell Press 2017 Cell systems Vol.4 No.5

Effective development of host cells for therapeutic protein production is hampered by the poor characterization of cellular transfection. Here, we employed a multi-omics-based systems biotechnology approach to elucidate the genotypic and phenotypic differences between a wild-type and recombinant antibody-producing Chinese hamster ovary (CHO) cell line. At the genomic level, we observed extensive rearrangements in specific targeted loci linked to transgene integration sites. Transcriptional re-wiring of DNA damage repair and cellular metabolism in the antibody producer, via changes in gene copy numbers, was also detected. Subsequent integration of transcriptomic data with a genome-scale metabolic model showed a substantial increase in energy metabolism in the antibody producer. Metabolomics, lipidomics, and glycomics analyses revealed an elevation in long-chain lipid species, potentially associated with protein transport and secretion requirements, and a surprising stability of N-glycosylation profiles between both cell lines. Overall, the proposed knowledge-based systems biotechnology framework can further accelerate mammalian cell-line engineering in a targeted manner.

Parental, Perinatal, and Childhood Risk Factors for Development of Irritable Bowel Syndrome: A Systematic Review

( En X S Low ),( Maimouna N K Al Mandhari ),( Charles C Herndon ),( Evelyn X L Loo ),( Elizabeth H Tham ),( Kewin T H Siah ) 대한소화기기능성질환·운동학회(구 대한소화관운동학회) 2020 Journal of Neurogastroenterology and Motility (JNM Vol.26 No.4

Background/Aims Adverse early life experiences are associated with the development of stroke, cancer, diabetes, and chronic respiratory and ischemic heart diseases. These negative experiences may also play a role in the development of irritable bowel syndrome (IBS)--a functional gastrointestinal disease. This review discusses the research to date on the parental, perinatal, and childhood risk and protective factors associated with the development of IBS. Methods A literature search was completed for studies published between 1966 and 2018 that investigated premorbid factors occurring during the perinatal and childhood periods as well as parental factors that were associated with the development of IBS. Results Twenty-seven studies fulfilled the review criteria. Risk factors that appeared in more than one study included: (1) parental IBS, substance abuse, parental punishment, and rejection as parental risk factors; (2) low birth weight as a perinatal risk factor; and (3) crowded living conditions in low-income families, childhood anxiety, depression, or child abuse as childhood risk factors. Protective factors for IBS were emotional warmth from the parents and being born to an older mother. Conclusions More effort is needed to identify what fetal and maternal factors are associated with low birth weight and IBS. A well-executed prospective birth cohort with a collection of bio-samples and functional data will provide a better understanding of how adversity and the interplay between genetics, epigenetics, and numerous risk factors affect the development of IBS. (J Neurogastroenterol Motil 2020;26:437-446)