大功率晶体管在超声发生器中的应用

Ｃ３大功率晶体管在超声发生器中的应用苑雷（无锡市超声电子设备厂无锡·２１４０３５）品体管超声发生器越来越普遍地应用到各行各业，晶体管发生器的基本电路已为大多数人所掌握，但仍然存在一些问题，如晶体管的温升高、失效率高等这些问题的存在降低了晶体管发生器的...     

新型大功率MOSFET及其应用

功率TMOS和VMOSFET是近几年才出现的新型大功率电子器件。由于它集中了电子管、双极型晶体管及可控硅的优点,在耐压、电流方面可和大功率晶体管相提并论,并且有输入阻抗高,开关速度快,没有二次击穿,激励电路极为简单等优越性能,因而在国内外受到人们的极大关注。 本文从MOSFET的结构、工艺、物理性质等方面,简要地介绍了它的优点及目前实际应用的领域。由于它很适合于宽频带工作,适应于负载的各种变化,不存在二次击穿的现象,故特别适用于各种大功率转换电路。我们将功率VMOSFET用于声纳发射机功放电路,并以此作为例子,进一步阐明了器件的优越性能,解决了以前很难解决的问题,使机器可靠性得到了较大的提高。 本文也指出了在实际应用中应注意的事项。     

新型零电压开关多谐振变换器

论述了一种新型多谐振变换器．通过开关型吸收电路使晶体管电压应力大大降低．理论分析和实验结果证明该变换器具有更优越的工作性能．     

高稳定度大功率开关稳压调压电源

高稳定度大功率开关稳压调压电源我所同四川迈科高技术开发中心共同研制成功的高稳定度大功率开关稳压电源，有稳压、调压功能，可以代替雷达发射机中的ｄｅＱ电路，对提高发射机的频率稳定度和整机性能能起到良好作用。该电源已在雷达发射机上得到应用。高稳定度大功率开...     

晶体管开关参数标准装置测试夹具的设计

晶体管开关参数标准装置主要用于测量双极型中小功率晶体开关管的时间参数,如开启时间ton和关闭时间toff等。本文介绍了晶体管开关参数测量的基本电路、参数计算及标准装置中测试夹具在电路设计和结构设计上的特点。     

晶体管开关参数标准装置测试夹具的设计

晶体管开关参数标准装置主要用于测量双极型中小功率晶体开关管的时间参数,如开启时间ton和关闭时间toff等.本文介绍了晶体管开关参数测量的基本电路、参数计算及标准装置中测试夹具在电路设计和结构设计上的特点.     

变频空调缺陷：引起电网谐波污染及其危害

目前市场中采用交流变频技术的家用空调的核心是变频器，变频器就是电网中的非线性负载，其运行过程中工频电源整流成直流电压信号，经电容滤波及大功率晶体管开关元件逆变为频率可变的交流信号。在整流电路中，输入电流的波形为不规则的矩形波，波形按傅立叶级数分解为基波和各次谐波，其中的高次谐波将干扰输入供电系统。输出回路电流信号也可分解为只含正弦波的基波和其它各次谐波，谐波与电力系统中基波叠加，造成波形畸变从而引起电网谐波污染。     

开关功率变换器中的混沌现象研究

本文对开关功率变换器中的混沌现象进行了探讨，并在电路实验和计算机模拟两个方面证明了开关功率变换器不仅在ＰＷＭ闭环控制下会出现混沌现象，而且在开环工作情况下，由于功率晶体管极间电容的非线性等因素的影响，功率变换器也可能出现混沌。     

可控硅稳发射装置的研制

一、引言 目前常用的电离真空计稳发射装置几乎都采用大功率晶体管串连线性调整型式。这种电路虽具有稳定度高,输出电压纹波较低等优点,但由于调整管必须工作在线性区域,而作为灯丝加热的电源必须具有大的加热电流(2～5A),造成调整管的功耗也相当可观。因此一般真空计都带有体积庞大的散热罩;DC—3型真空计为解决调整管散热问题,还专门设置了风冷设施;但在真空计长时间工作的条件下,仍会出现调整管因过热而损坏的现象。开关型晶体管稳发射装置[1],[2]基本解决了连续型稳发射电源调整管功耗大的缺点。但由于这种类型的电路比较复杂,对于推…     

加拿大学者发明原子开关将给计算机带来变革

正加拿大阿尔伯塔大学国家纳米中心和德国马克斯·普朗克研究所的联合研究团队,制造出比目前市场上最小的开关或晶体管还要小近100倍的原子开关,将会带来更小、超高效的计算机。相关研究成果发表在今年10月26日的《自然通讯》(Nature Communications)杂志上。计算机中使用的晶体管是电路中用于控制电子流动的关键阀门。目前最小的晶体管约14     

固相剪切碾磨制备聚丙烯/废旧橡胶/聚烯烃弹性体复合材料

利用固相剪切碾磨技术在常温下制备了聚丙烯(PP)/废旧轮胎橡胶(GTR)/聚烯烃弹性体(POE)复合材料。采用力学性能测试、差热分析(DSC)和扫描电镜(SEM)对固相剪切碾磨制备的GTR/POE复合粉体和相应PP/GTR/POE复合材料进行表征和分析,研究了碾磨次数和GTR/POE含量对PP/GTR/POE复合材料结构与性能的影响。结果表明,对固相剪切碾磨方法制备的PP/GTR/POE复合材料,GTR和POE被有效粉碎和均匀分散,其冲击强度和断裂伸长率比常规熔融共混方法制备的复合材料高;增加GTR/POE共碾磨复合粉体的含量或增加碾磨次数均可提高冲击强度和断裂伸长率。     

In vitro aging of mineralized collagen-based composite as guided tissue regeneration membrane

The technique of guided tissue regeneration (GTR) has been developed for the regeneration of periodontal tissues, bone around natural teeth and dental implants. The aim of this study is to investigate the biodegradability and mechanic behavior of a novel mineralized nano-hydroxyapatite/collagen/poly (lactic acid) (nHAC/PLA) composite as GTR membrane in vitro. The elastic modulus and maximum tensile strength of GTR film samples with different nHAC/PLA ratio were measured to get an optimal nHAC/PLA ratio. Thermogravimetric analysis was conducted to evaluate the change of the inorganic component in the samples during the process of in vitro aging. Morphology of samples was checked by using scanning electron microscopy. On the basis of the above results, it can be concluded that the GTR membranes maintained integrity and the original appearance throughout the 1-month in vitro aging. There is an active dissolution and deposition process of crystals which is propitious to the bone formation on the surface of the composite membrane. The optimal nHAC/PLA ratio of the novel membrane is 0.4:1. For a longer period of bone repair, PLA with higher molecular weight should be chosen as the scaffold for the GTR membrane.     

Mechanical,rheological, morphological and water absorption properties of maleated polyethylene/hemp composites: Effect of ground tire rubber addition

Natural fibre composites were produced from maleated polyethylene (MAPE) and hemp fibres, while impact modification was performed via ground tire rubber (GTR) addition. Incorporation of hemp fibre increased significantly the tensile (strength and modulus) and flexural properties of the MAPE matrix. Impact strength however, decreased with increasing hemp content, but GTR addition led to a noticeable increase in impact strength (up to 50% at 10% GTR). Increase in hemp content produced also higher water uptake and longer saturation time. After ageing in water, the mechanical properties and thermal stability were unchanged for samples up to 30% hemp, but samples at higher concentrations showed some degradation.     

Ground tyre rubber (GTR) in thermoplastics, thermosets, and rubbers

The disposal of worn tyres and their economic recycling mean a great challenge nowadays. Material recycling is the preferred way supported by legislative actions and economical/ecological arguments. This paper surveys the recent developments devoted to the reclamation, surface treatments, and to the use of ground tyre rubber (GTR) in thermoplastics, thermosetting resins, and rubber formulations. This review discloses also the principle underlying compatibilization to improve the adhesion of GTR to the corresponding matrix. It was concluded that value-added application of GTR can especially be expected in thermoplastic elastomers, and rubber combinations.     

A novel process for heavy plate: gradient temperature rolling,fast cooling,tempering

In order to develop ultra-heavy plates with high strength, a novel short process without quenching was proposed in this paper based on gradient temperature rolling (GTR), fast cooling and tempering. The results show that, from plate surface to centre, yield strength of uniform temper rolling specimens exhibits a gradual decrease, and yield strength at quarter thickness is 30?MPa higher than in the centre in tempered sample. However, the yield strength of as-rolled GTR plates represents a small increase, indicating a new strength distribution of heavy plate. The optimal process-steps were GTR, fast cooling and 650°C tempering, which satisfies the requirement of Q890E heavy plates standard.     

Effects of hydroxyapatite and PDGF concentrations on osteoblast growth in a nanohydroxyapatite-polylactic acid composite for guided tissue regeneration

The technique of guided tissue regeneration (GTR) has evolved over recent years in an attempt to achieve periodontal tissue regeneration by the use of a barrier membrane. However, there are significant limitations in the currently available membranes and overall outcomes may be limited. A degradable composite material was investigated as a potential GTR membrane material. Polylactic acid (PLA) and nanohydroxyapatite (nHA) composite was analysed, its bioactive potential and suitability as a carrier system for growth factors were assessed. The effect of nHA concentrations and the addition of platelet derived growth factor (PDGF) on osteoblast proliferation and differentiation was investigated. The bioactivity was dependent on the nHA concentration in the films, with more apatite deposited on films containing higher nHA content. Osteoblasts proliferated well on samples containing low nHA content and differentiated on films with higher nHA content. The composite films were able to deliver PDGF and cell proliferation increased on samples that were pre-absorbed with the growth factor. nHA–PLA composite films are able to deliver active PDGF. In addition the bioactivity and cell differentiation was higher on films containing more nHA. The use of a nHA–PLA composite material containing a high concentration of nHA may be a useful material for GTR membrane as it will not only act as a barrier, but may also be able to enhance bone regeneration by delivery of biologically active molecules.     

仪器误差符合性测试中的风险控制方法

在仪器误差符合性测试过程中,需要通过测量结果给出被测仪器设备合格与否的判定。由于测量不确定度的存在,会导致误判的可能,从而给用户和厂家带来决策风险。为了确保厂家风险（PR）及用户风险(CR)可控,提出了过程能力指数(PCI)、测试不确定度比(TUR)、保护带允许误差比(GTR)综合控制方法,建立了这3个参数与厂家风险和用户风险间的关系,并通过图形化方式给出了实际测试过程风险控制准则。仿真结果表明,在一定的过程能力指数下,选择适当的不确定度比和置信区间保护带,可以满足CR和PR期望值要求。     

轮胎胶高剪切应力诱导脱硫反应的影响因素

采用在轮胎胶粉与三元乙丙橡胶(EPDM)混合物的熔融挤出过程中提高双螺杆挤出机螺杆转速的高剪切应力诱导方法,研究了轮胎胶粉品种和烷基酚多硫化物促进剂对轮胎胶脱硫共混物的凝胶含量、溶胶分子链结构及脱硫共混物共混丁苯橡胶再硫化材料力学性能的影响。试验结果表明,胶粉品种对所得脱硫共混物溶胶中的双键含量及再硫化材料的拉伸强度具有重要影响;烷基酚多硫化物促进剂420和450具有明显促进脱硫反应和抑制交联副反应的作用,有效减小再硫化材料凝胶粒子尺寸,聚合型促进剂450兼具有抗氧化降解和抑制加成副反应的功能。     

8098单片机在PWM整流电源中的应用

本文提出一种新的整流电源的控制策略，它可以使整流电源在工作时，从电网输入的电流近似为正弦波，功率因数为１．该控制系统采用８０９８单片机为主体，使所需的接口硬件减少到最少．本控制系统可用于象ＧＴＲ这样具有较高开关速度的大功率电源系统的控制．     

Development of asymmetric gradational-changed porous chitosan membrane for guided periodontal tissue regeneration

A novel kind of guided tissue regeneration (GTR) barrier membrane has been fabricated using an immersion–precipitation phase inversion technique (IPPI) with biodegradable natural polymer–chitosan. The membrane had an asymmetric gradational-changed porous structure including a dense skin layer, a transition region and a sponge-like porous layer. The concentration of chitosan solution and solvent evaporated time were two key factors that had significant effect on the porosity, average pore size, absorbed water ratio and mechanical properties of the porous membrane. The porous membrane not only degraded but maintaining the structure integrity for 5–6 weeks in the enzyme solution that can meet the demand for GTR. The biological experiment results showed the asymmetric membranes did not cause anaphylactic reaction, hemolysis, cytotoxicity and pyrogenic effect. All of the results indicated that the porous chitosan membrane had excellent biocompatibility and biodegradation, which could be used as a barrier for preventing apical migration of gingival epithelial cells and promoting growth of periodontal ligament cells in periodontal therapy.