充电器大功率变压器的设计

介绍开关电源高频大功率变压器设计的材料选择、计算方法和过程,并给出了一个充电器大功率变压器的设计实例,实验证明该变压器符合实际要求。     

Optimum design of a high-power, high-frequency transformer

A procedure for optimum design of a high-power, high-frequency transformer is presented. The procedure is based on both electrical and thermal processes in the power transformer and identifies: (a) the VA-rating of ferrite cores in relation to the operating frequency; (b) the optimum flux density in the core; and (c) the optimum current densities of the windings providing maximum transformer efficiency. Since the transformer is the major contributor to the volume and weight of the power supply, the results of transformer analysis can be used for entire power supply optimization as well. Two high-power, high-frequency transformers are optimally designed, built, and tested. Practical results show good agreement with the theory     

氮化镓功率半导体器件技术

作为第三代半导体材料的典型代表,宽禁带半导体氮化镓(GaN)具有许多硅材料所不具备的优异性能,是高频、高压、高温和大功率应用的优良半导体材料,在民用和军事领域具有广阔的应用前景。随着GaN技术的进步,特别是大直径硅(Si)基GaN外延技术的逐步成熟并商用化,GaN功率半导体技术有望成为高性能低成本功率技术解决方案,从而受到国际著名半导体厂商和研究单位的关注。总结了GaN功率半导体器件的最新研究,并对GaN功率器件发展所涉及的器件击穿机理与耐压优化、器件物理与模型、电流崩塌效应、工艺技术以及材料发展等问题进行了分析与概述。     

Cosine pattern synthesis for single and multiple main beamuniformly spaced linear arrays

The method of cosine pattern synthesis for single- and multiple-main-beam equispaced linear arrays is introduced. The cosine pattern function is characterized by the position of the main beam in the &thetas;-domain and its half-power beamwidth. The Fourier series and Woodward-Lawson methods are applied to the special cases of single- or multiple-main-beam cosine pattern synthesis. The patterns produced by application of these classical shaped-beam synthesis methods can then be used as initial patterns for iterative and perturbational techniques. Examples are presented and discussed, including the use of multiple-main-beam cosine pattern synthesis to design a high-power, high-frequency, ground-based transmitter for the creation of an array of `wireless' ionospheric dipoles     

Harmonic emission from high-power high-frequency gyrotrons

The results of a study of second-harmonic emission from a gyrotron designed for high-power high-frequency operation at the fundamental of the cyclotron frequency are presented. Stable, very narrow bandwidth second-harmonic cavity emission from 209 GHz to 302 GHz has been observed. An output power of 25 kW and efficiency of 6·5% in the TE_{11, 2, 1}, mode at 241 GHz is reported; this represents the highest power obtained to date from a high-frequency (> 100 GHz) harmonic gyrotron. These experiments have been carried out in a cavity for which the mode density is very high; the cavity diameter is approximately six free-space wavelengths for emission at the second harmonic. Mode competition between fundamental and second-harmonic modes is discussed. It is also shown that, in general, gyrotrons designed for high-power low-Q operation in overmoded cavities at the fundamental will also have high efficiencies and strong emission in second-harmonic modes. Prospects for high-frequency harmonic gyrotrons for plasma diagnostics and other applications are described     

Electron-optical systems with planar field-emission cathode matrices for high-power microwave devices

Reasons for limits on application of field-emission structures in high-power microwave vacuum tubes are studied on the basis of the performed analysis and the methods for their overcoming are discussed. Prospects for application of planar end field-emission structures (PEFESs) as a long-lived current source in high-power vacuum microwave amplifiers are substantiated. The results of design of the proposed electronoptical system with cathode matrices consisting of PEFES cells, which forms electron flows with a power over 100 kW in the contiuous-wave operating conditions, are presented.     

A Novel Method for High-Power Thermal Vacuum Testing of Satellite Payloads Using Pickup Horns

This paper presents the development of a novel method for high-power thermal vacuum (TVAC) testing of satellite payloads using pickup horns (PUH). It describes the design, manufacture, and qualification results for a Ku-band pickup horn, followed by high-power thermal vacuum test results of a Ku-band satellite for fixed satellite service. Based on the successful demonstration of this method, a generic pickup horn (GPUH) - with improved performance over a large bandwidth, covering 7.0 GHz to 21.0 GHz - was developed for testing of X-band, Ku-band, and Ka-band satellite payloads. Detailed design and qualification aspects of the generic pickup horn are addressed, including measured results. This method has been successfully employed for high-power thermal vacuum testing of three different satellites at Lockheed Martin Commercial Space Systems (LMCSS), and is the planned testing method for all future payloads.     

Scaling of longitudinally diode-pumped self-frequency-doublingNd:YCOB lasers

We report the scaling of a new self-frequency-doubling laser, based on the crystal Nd³⁺:YCa₄O(BO₃) ₃, to higher powers. The power scaling is achieved by diode pumping using a novel technology of combining the output of up to four high-brightness laser diodes. Spectroscopic, thermo-mechanical, and laser properties are investigated for use in designing high-power self-frequency-doubling lasers. Using a method of angular-multiplexing individual laser diodes for pumping, we demonstrate output powers of more than 1.9 W of fundamental (1060 nm) radiation and 245 mW at the second harmonic. Experimental investigation rendered a thermal stress resistance figure-of-merit for this material to be between 210-280 W/m     

Rounded Corners in Microwave High-Power Filters and Other Components

Microwave high-power filters must be operated with internal air pressures of at least one atmosphere, or with a good vacuum. Pressures between these extremes result in reduced powerhandling ability. The breakdown processes for both high air pressure and vacuum are discussed, and it is made clear that any sharp corner on which the electric field would concentrate must be rounded if high-power operation is to be achieved. For good results in vacuum operation, the surfaces must be especially smooth and free of contamination, while in high-pressure operation, minor irregularities are less important. Various high-power filter configurations of importance are described, and the structural corners at which electric-field concentrations occur are pointed out. A number of simplified geometries are then shown that can represent the essential portions of the practical structures with sufficient accuracy for ordinary purposes. Formulas and graphs for these simplified geometries are presented that give the ratio of the maximum electric field strength on the boundary to a uniform reference field strength at a point sufficiently removed from the corner. In some cases, the boundary curve is an approximation to a circular arc, while in other cases a boundary shape is derived such that the electric field strength along the curve is constant. These constant-field-strength boundaries are optimum shapes from the standpoint of power-handling ability.     

一种利用有限元法模拟LED芯片结点温度的方法

提出了一种以有限元法估算发光二极管(LED)光源模块结点温度的方法,提出了较详细的计算步骤,最后以6只1 W大功率LED组成的光源模块为例,演示如何以实测为基础,实测与软件试算相结合来估算LED光源模块的芯片结点温度.结果证明该方法具有较好的预测性,可以用来研究LED光源模块的温度分布,从而为研究LED封装材料匹配性、系统可靠性提供一定的参照.     

AlGaN/GaN基HEMT器件的研究进展(英文)

由于AlGaN具有高的击穿电场(3 MV/cm,是GaAs的7.5倍),且在AlGaN/GaN异质结处存在高浓度的极化诱导二维电子气,AlGaN基高电子迁移率晶体管是目前最适合应用于微波大功率放大领域的器件。着重对影响高频大功率AlGaN/GaN性能的材料结构和器件制作进行了阐述。     

Coaxially wound transformers for high-power high-frequencyapplications

Design considerations for transformers utilized in high-power high-frequency DC/DC converters are addressed. Major areas of concern are core-material selection, minimization of copper losses due to skin and proximity effects, and the realization of controlled leakage inductances. Coreless characteristics for various high-frequency materials are presented, and the influence of various conventional winding arrangements on the copper losses and leakage field is also demonstrated. Coaxial winding techniques (used commonly in high-frequency transformers) are investigated next as a feasible solution for containing the leakage flux within the interwinding space, thus preventing it from permeating the core and resulting in lower core losses and the avoidance of localized heating. Added benefits of this technique are reduced forces within the transformer, lower copper losses, and robust construction. The performances of two experimental single-phase 50 kW, 50 kHz units are reported. A three-phase version of coaxially wound transformers is also presented     

Passive mode locking of lasers with the optical Kerr effect modulator

A detailed analytical investigation is presented of a nonlinear device termed the optical Kerr effect modulator (OKEM) which is used to passivelyQswitch and mode lock high-power lasers. Experimentally, an OKEM employing two standard quarter-wave plates is used to passively mode lock the Nd:glass laser. The mode-locking threshold dependence upon the parameters of the OKEM transmission function is definitively established. Pulsewidths and spectral measurements are given for the train of ultrashort pulses from the glass laser mode locked with the OKEM using two different Kerr liquids. The analytical and experimental results together indicate that the OKEM technique is a versatile and viable alternative and in addition overcomes most of the shortcomings intrinsic to the saturable absorber technique. The non-resonant nature of the OKEM suggests that it should find immediate application as a passiveQ-switching and mode-locking element for a Variety of lasers, including dye lasers, UV lasers, the CO2laser, and, notably, the high-power iodine laser.     

High-frequency limitations of abrupt-junction FET's

This paper represents analytical results concerning the high-frequency limitations of FET's of junction-gate or Schottky-gate constructions. The intrinsicyparameters are calculated in closed form using the analog RC transmission line method. The bias dependence of various characteristic factors in the y parameters expressions are presented graphically. Equivalent networks including both the intrinsic and extrinsic resistance-capacitance elements are presented and used to calculate the power-gain and frequency limitations of FET's.     

High-reliability microwave silicon power transistor with stepped electrode structure and TiN diffusion barrier

A high-reliability microwave silicon power transistor is described that has a stepped electrode structure and TiN diffusion barrier. This structure, used for high-power and high-frequency devices, is discussed by comparing it to the conventional planar structure. The new structure permits microwave devices to achieve high levels of performance. For high-power dissipation devices having a beam lead metal system, however, the Au-Si reaction and localized Pt-silicide growth are major failure mechanisms. To improve these failures, the Ti layer must be thickened and further TiN applications in beam lead metal systems are discussed. Experimental results of high-temperature long-term operations proved that high-power microwave transistors with excellent reliability can be obtained by using a stepped electrode structure with TiN diffusion barrier.     

SiC电力电子技术综述

与硅相比,4H-SiC材料具有高功率、耐高温、高频、高集成度、高效率、高抗辐射等优势,是制作电力电子器件的理想材料,近十年以来SiC电力电子器件性能不断提高.回顾了SiC电力电子器件的发展,总结了材料、工艺和器件所面对的技术问题.笔者认为SiC JBS二极管和MOSFET将成为SiC的主流器件,将在今后十年内获得长足的...     

Reduction of common-source inductance in FET/HEMT structuresutilizing wave-propagation effects

In this paper, a novel high-frequency/high-power field-effect-transistor structure is presented to reduce gain degradation caused by common-source inductance. In this structure, the reduction in common-source inductance is achieved without the need for using very thin substrates or very complicated fabrication technology, such as vias under each source finger. Using detailed transmission-line modeling, it is shown that a significant reduction in common-source inductance and improvement in RF performance can be achieved even for moderately high values of source grounding via inductance. The new structure allows simpler fabrication technology and is expected to be particularly useful to reduce the cost and improve the performance of high-power microwave and millimeter-wave devices and circuits     

A Study of Nonlinearities and Intermodulation Characteristics of 3-Port Distributed Circulators

Results of a study of nonlinearities and intermodulation characteristics of 3-port distributed circulators are presented. Based on a rigorous theoretical analysis of the third-order nonlinearity in ferrites, analytical results are derived for the field strength and the power level of the intermodulation signal. These explicit results are applicable to high-power distributed circulators operating in VHF, UHF, and microwave frequencies. Measured intermodulation characteristics of an experimental distributed VHF high-power circulator are also presented.     

Reliability of Contacts for Press-Pack High-Power Devices

Reliability of high-power silicon diodes with different anode contact material (Al, PtSiCu, PtSiCuAu) was tested in the conditions of free-floating silicon in pressed package. Pressure, thermal and cycling tests were applied without foils to buffer excessive loading. Thin PtSi layer was found too brittle for usage in so hard conditions. Copper stacks with thin PtSi interlayer provide low voltage drop and show potential to survive such hard stress conditions under thermal and power load cycle. 5 μm thick PtSiCu contacts showed the best thermo-mechanical properties.     

An original approach to mode converter optimum design

An original method of shape optimization has been developed to improve high-power high-frequency transmission lines' performances. This method is based on the coupling coefficients equations, for which general expressions are given. It makes use of numerical methods such as steepest descent associated to adjoint state technique. The results obtained on several types of components demonstrate the pertinence of this method