1,720,967 research outputs found
Study of the Asymmetrical Half Bridge Flyback Converter as an Effective Line Fed Solid State Lamp Driver
No full textThe paper illustrates the design and experimental test of a line fed, solid state lamp driver based on the asymmetrical half bridge (AHB) flyback converter. The favorable converter’s characteristics, in terms of soft-switching range and circuit complexity, allow it to operate at variable switching frequency in the range 300-450 kHz, supplying 6W to the load with good efficiency. The considered lamp is made up of 5 series connected high power LEDs (Cree XR-E) and is supplied with 350 mA closed loop regulated, constant current. While presenting similar complexity and overall efficiency with respect to a conventional driver, thanks to an original feedforward control technique that allows to shrink the input filter capacitor, the proposed circuit allows a significant volume reduction and consequent power density improvemen
Das Ende des objektiven Geistes. Die Ueberwindung des objektiven Geistes im absoluten Geistes nach Hegels Enzyklopaedie der philosophischen Wissenschaften
No full textAnalysis and Optimization of the AHB-Flyback Topology for Solid State Lighting Applications
No full textIn this paper a single stage AC/DC converter, based on the asymmetrical half bridge (AHB) flyback topology, is proposed as a line fed HBLED lamp ballast. Simplicity and reduced component count, together with high switching frequency operation (300-450kHz), effectively determine significant volume reduction and higher power density with respect to conventional circuits. Moreover, thanks to zero
voltage switching and frequency modulation, high efficiency can be achieved, making the proposed topology an attractive solution for HBLED driving. The converter can be designed to operate with a significant input voltage ripple, allowing input filter capacitance reduction and compliance with the EN61000-3-2 standard. Converter operation principles and boundary conditions among the different topological phases have been analyzed. Feed-forward and feedback techniques have been investigated to optimize converter operating
conditions, improve efficiency and minimize the current ripple through the lamp. A prototype has been built and tested; experimental results are reported
Line Fed Solid State Lamp Driver Based on the Asymmetrical Half Bridge Flyback Converter
No full textThe paper illustrates the design and operation of a line fed, solid state lamp driver based on the asymmetrical half bridge (AHB) flyback converter. The favorable converter’s characteristics, in terms of softswitching range and circuit complexity, allow it to
operate at variable switching frequency in the range 300-450 kHz, supplying 6W to the load. The lamp is made up of 5 series connected high power LEDs (Cree XR-E) and is supplied with 350 mA closed loop regulated, constant current. While presenting similar complexity and overall efficiency with respect to a conventional driver, the proposed circuit allows a significant volume reduction and consequent power density improvement
A Novel Double Integrated Buck Offline Power Supply for Solid State Lighting Applications
No full textA single stage offline power supply for LED lighting applications, based on the integration of a buck PFC and a tapped buck DC/DC converter, is presented in this paper. Besides the high step-down capability and output current regulation, the proposed topology effectively provides power factor correction, so as to comply with the harmonic injection and energy saving standards EN 61000-3-2 and Energy Star. The low BUS voltage level, resulting from the use of an input step-down PFC stage, actually allows the use of film technology capacitors, instead of short lifetime electrolytic capacitors, to filter the BUS voltage and reduce the LED current ripple component at twice the line frequency. Thanks to the high reliability, the simple structure, the good line side spectral performance and the low component count, the proposed topology effectively results to be very suitable for medium power solid state lighting applications, as in the case of LED down-lighting.
The issues related to the operation of the presented solution and to its design optimization will be carefully discussed. A
prototype of the proposed AC/DC converter has been built and
tested. The main experimental results will be described
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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