1,721,502 research outputs found
Self-Sustained Turn-OFF Oscillation of Cascode GaN HEMTs:Occurrence Mechanism, Instability Analysis, and Oscillation Suppression
Full text linkThis article presents a comprehensive study on the occurrence mechanism, instability analysis, and suppression methods of self-sustained turn-off oscillation, which occurs on cascode gallium nitride high electron mobility transistors (cascode GaN HEMTs). In the beginning, the oscillation waveforms are analyzed, which indicate that the occurrence of the oscillation is determined by test circuit instability. Based on the double pulse test, the impact of the load current I_L, dc bus voltage V-{text{DC}} and gate resistance R-{G} on the self-sustained oscillation is identified. To investigate the instability of the resonant circuit, a small-signal ac model of the resonant circuit is derived. Based on the model, the influences of various parameters on the self-sustained oscillation are analyzed. The analyses reveal the possible methods which can suppress the oscillation. The effectiveness of the proposed methods is validated by the experimental data and simulation results in the end. </p
Ferrite Beads Design to Improve Turn-off Characteristics of Cascode GaN HEMTs:An Optimum Design Method
Full text linkIn this article, an optimum ferrite beads design method is proposed to suppress the self-sustained turn-off oscillation of cascode gallium nitride high-electron-mobility transistors (GaN HEMTs). At first, the impacts of gate loop beads and power loop beads on the turn-off oscillation of cascode GaN HEMTs are analyzed. The analysis reveals the weak damping effect of gate loop beads on the turn-off oscillation. Next, an analytical method is proposed to design the power loop beads that can achieve maximum effective damping on the turn-off oscillation. The power loop beads introduce extra stray inductance in the power loop, which can induce high-voltage overshoot. To tackle the problem, an optimum design method is proposed, so that the power loop beads can suppress the oscillation while mitigating the voltage overshoot. The accuracy of the proposed model is validated by the experimental data in the end.</p
Analysis on the Self-Sustained Oscillation of SiC MOSFET Body Diode
No full textUnder certain conditions, self-sustained oscillation may occur during reverse recovery transient of high-side silicon carbide (SiC) MOSFET body diode in the half-bridge circuit. In this article, two distinct positive feedback mechanisms that can excite the self-sustained oscillation are identified based on the double-pulse test. To investigate the instability of the two types of oscillation, a small signal ac model of the half-bridge circuit is proposed. With the model utilized, the parametric sensitivities of various parameters on the self-sustained oscillation are analyzed. The analyses reveal the oscillatory criteria, which provides effective guidelines to prevent the oscillation. In the end, the oscillation prevention guidelines are validated by the experiment. The experimental results demonstrate that the proposed theoretical treatment can provide reasonable guidelines to suppress the two types of self-sustained oscillation
Investigation on the Self-Sustained Oscillation of Superjunction MOSFET Intrinsic Diode
No full textThis paper presents the analyses on the self-sustained oscillation of superjunction MOSFET intrinsic diode. At first, the characteristics of the self-sustained oscillation for the superjunction MOSFET intrinsic diode are identified by the double-pulse switching test. The test results show that the self-sustained oscillation with significant self-amplification phenomenon can be triggered during the reverse recovery transient of superjunction MOSFET intrinsic diode. Based on the Sentaurus TCAD simulation, the self-sustained oscillation is reproduced. The simulation results reveal the root cause of the self-sustained oscillation. Due to the snappy reverse recovery of superjunction MOSFET intrinsic diode, the steep slope of diode snap off current can generate high voltage across the common source inductance, which drives the gate-source voltage and turns on the high-side MOSFET. The unexpected MOSFET turn-on can, in return, enhance the steepness of the current slope when the diode snap off. This leads to a positive feedback process and self-sustained oscillation is generated. In the end, based on the theoretical analyses and experimental results, the necessary methods that can suppress the oscillation are presented
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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