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161.
This paper presents a load adaptive soft-start scheme through which the inductor current of the synchronous boost DC-DC converter can trace the load current at the start-up stage. This scheme effectively eliminates the inrush-current and over-shoot voltage and improves the load capability of the converter. According to the output voltage, the start-up process is divided into three phases and at each phase the inductor current is limited to match the load. In the pre-charge phase, a step-increasing constant current gives a smooth rise of the output voltage which avoids inrush current and ensures the converter successfully starts up at different load situations. An additional ring oscillator operation phase enables the converter to start up as low as 1.4 V. When the converter enters into the system loop soft-start phase, an output voltage and inductor current detection methods make the transition of the phases smooth and the inductor current and output voltage rise steadily. Effective protection circuits such as short-circuit protection, current limit circuit and over-temperature protection circuit are designed to guarantee the safety and reliability of the chip during the start-up process. The proposed start-up circuit is implemented in a synchronous boost DC-DC converter based on TSMC 0.35μm CMOS process with an input voltage range 1.4-4.2 V, and a steady output voltage 5 V, and the switching frequency is 1 MHz. Simulation results show that inrush current and overshoot voltage are suppressed with a load range from 0-2.1 A, and inductor current is as low as 259 mA when the output shorts to the ground. 相似文献
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163.
The objective of this study is to investigate a high performance and lower cost compact gamma camera module for a multi-head small animal SPECT system. A compact camera module was developed using a thin Lutetium Oxyorthosilicate (LSO) scintillation crystal slice coupled to a Hamamatsu H8500 position sensitive photomultiplier tube (PSPMT). A two-stage charge division readout board based on a novel subtractive resistive readout with a truncated center-of-gravity (TCOG) positioning method was developed for the camera. The performance of the camera was evaluated using a flood 99roTe source with a four-quadrant bar-mask phantom. The preliminary experimental results show that the image shrinkage problem associated with the conventional resistive readout can be effectively overcome by the novel subtractive resistive readout with an appropriate fraction subtraction factor. The response output area (ROA) of the camera shown in the flood image was improved up to 34%, and an intrinsic spatial resolution better than 2 mm of detector was achieved. In conclusion, the utilization of a continuous scintillation crystal and a flat-panel PSPMT equipped with a novel subtractive resistive readout is a feasible approach for developing a high performance and lower cost compact gamma camera. 相似文献
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165.
“神光”Ⅲ装置中主放大级采用大口径等离子体电极的电光开关作系统隔离单元,主要抑制反向激光束和其他杂散光束。它主要由普克尔盒(PEPC)、两台等离子体脉冲发生器、开关脉冲发生器等组成。等离子体发生器由预燃脉冲和放电脉冲产生电路组成。预燃脉冲触发预电离后维持一定的电压和电流,持续时间0.5s。在预燃脉冲的0.4s处触发闸流管以形成脉冲放电等离子体。两台等离子体发生器要求同步,电流起点的偏离≤50ns。 相似文献
166.
一种改进的奇异值降噪阶次选取方法用于紫外光谱信号去噪的研究 总被引:1,自引:0,他引:1
光谱去噪是光谱检测的重要环节。针对光谱信号易受光谱仪热噪声、现场机械振动以及随机噪声等因素影响,而在线监测系统要求减少人为参数选择对去噪效果的影响,提出利用奇异值分解(SVD)理论对光谱信号去噪。提出一种改进的降噪阶次选取方法:指定奇异值差分谱最大峰值点θ1为所选阶次下界;利用奇异值、奇异值差分谱综合信息选取阶次上界θ2;将区间θ1~θ2定义为模糊区域,通过模糊C均值聚类求取隶属度,赋予模糊区域内奇异值相应的权重系数。用所提方法对不同信噪比下SO2紫外光谱信号去噪,将信噪比、均方根误差、波形相似系数、平滑度指标用于去噪效果的评价。去噪结果表明:所提方法完全基于数据驱动,具有较好的去噪效果,能够真实的恢复原始信号。 相似文献
167.
169.
Discrete Alfven eigenmodes in international thermonuclear experimental reactor operations with negative magnetic shear 下载免费PDF全文
Discrete Alfven eigenmodes in steady-state operation scenarios with negative magnetic shear in the international thermonuclear experimental reactor are investigated in this paper. These magnetohydrodynamic eigenmodes are trapped by the s-induced potential wells along the magnetic field line. Here α = -q2Rdβ/dr with q being the safety factor, the ratio between plasma and magnetic pressures, and R the major radius, and r the minor radius. Due to negligible continuum damping via wave energy tunneling, these Alfven eigenmodes could be readily destabilized by energetic particles. 相似文献
170.
基于社会比较情境下强者和弱者之间产生的同情、欺凌、漠然、尊敬、嫉妒和畏惧等6种情感,建立个体情感特征的定量表达方法。考虑情感驱动的三策略囚徒困境博弈模型,设计了6种情感与合作、背叛及孤独3个博弈策略之间的对应关系和定量表达机制。采用二维格子网络、随机网络和无标度网络等三种网络模型进行演化博弈仿真分析。结果显示:较大的背叛成功诱惑促进了采取背叛策略的情感类型发展演化和繁荣稳定,系统的最终演化状态都体现出程度不同的负性情感特征;空间网络结构对情感类型和合作行为的演化存在重要影响,无标度网络结构能够导致具有一定良性特征的情感类型演化稳定,并带来较高的合作水平;从社会比较及由此产生的对比效应和同化效应的角度,对三种网络下不同的情感演化状态进行了相应阐释。 相似文献