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High Voltage Power Supplies for Electrostatic ApplicationsCliff Scapellati, Vice President of EngineeringAbstract High voltage power supplies are a key component in electrostatic applications. A variety of industrial and scientific applications of high voltage power supplies are presented for the scientist, engineer, specifier and user of electrostatics. Industrial processes, for example, require significant monitoring of operational conditions in order to maximize product output, improve quality, and reduce cost. New advances in power supply technology provide higher levels of monitoring and process control. Scientific experiments can also be influenced by power supply effects. output accuracy, stability, ripple and regulation are discussed.Contributing effects such as output accuracy, stability, ripple and regulation are discussed.I.IntroductionThe use of high voltage in scientific and industrial applications is commonplace. In particular, electrostatics can be utilized for a variety of effects. Broadly stated, electrostatics is the study of effects produced by electrical charges or fields. The applications of electrostatics can be used to generate motion of a material without physical contact, to separate materials down to the elemental level, to combine materials to form a homogeneous mixture and other practical and scientific uses. By definition, the ability of electrostatic effects to do work requires a difference in electrical potential between two or more materials. In most cases, the energy required to force a potential difference is derived from a high voltage source. This high voltage source can be a high voltage power supply. Todays high voltage power supplies are solid state, high frequency designs, which provide performance and control unattainable only a few years ago. Significant improvements in reliability, stability, control, size reductions, cost and safety have been achieved. By being made aware of these improvements, the user of high voltage power supplies for electrostatic applications can benefit. Additionally, unique requirements of high voltage power supplies should be understood as they can affect the equipment, experiments, process or product they are used in. II.Operational Principles of High Voltage Power SuppliesA simplified schematic diagram of a high voltage power supply is shown in Fig.1.The input voltage source may have a wide range of voltage characteristics. AC sources of 50Hz to 400Hz at 100 megOhms are common. (This is to reduce power dissipation in the circuit and reduce the effects of temperature change due to self heating). The large resistance and the high voltage rating requires unique technology specific to high voltage resistors. The unique high voltage resistor must be paired with a low value resistor to insure ratio tracking under changes of temperature, voltage, humidity and time. In addition, the high value of resistance in the feedback network means a susceptibility to very low current interference. It can be seen that currents as low as 1 X 10-9 amps will result in 100ppm errors. Therefore, corona current effects must seriously be considered in the design of the resistor and the resistor feedback network. Also, since much of the resistor technology is based on a ceramic core or substrate, piezoelectric effects must also be considered. It can be demonstrated that vibrating a high voltage power supply during operation will impose a signal, related to the vibration frequency, on the output of the power supply.IV. Auxiliary Functions Involves With the High Voltage Power SupplyIn many applications of high voltage, additional control functions may be required for the instrument. The power supply designer must be as familiar with the electrostatics application as the end user. By understanding the application, the power supply designer can incorporate important functions to benefit the end process. A typical feature that can be implemented into a high voltage power supply is an ARC Sense control. Fig. 3 shows a schematic diagram of an arc sense circuit. Typically, a current sensing device such as a current transformer or resistor is inserted in the low voltage side of the high voltage output circuits. Typically, the arc currents are equal to: I = (E/R)(1)where I = Arc current in amperes. E = Voltage present at high voltage capacitor. R = Output limiting resistor in ohms. The arc current is usually much greater than the normal dc current rating of the power supply. This is due to keeping the limiting resistance to a minimum, and thereby the power dissipation to a minimum. Once the arc event is sensed, a number of functions can be implemented. Arc Quench is a term which defines the characteristic of an arc to terminate when the applied voltage is removed.Fig. 4 shown a block diagram of an arc quench feature.If shutdown is not desired on the first arc event, a digital counter can be added as shown in Fig.5.Shutdown or quench will occur after a predetermined number of arcs have been sensed. A reset time must be used so low frequency arc events are not accumulated in the counter. Example: A specification may define an arc shutdown if eight arcs are sensed within a one minute interval. A useful application of the arc sense circuit is to maximize the applied voltage, just below the arcing level. This can be accomplished by sensing that an arc has occurred and lowering the voltage a small fraction until arcing ceases. Voltage can be increased automatically at a slow rate.(Fig. 6)Another feature which can be found in the high voltage power supply is a highly accurate current monitor circuit. For generic applications this monitor feature may only be accurate to milliamperes, or microamperes. However, in some electrostatic applications accuracy down to femtoamperes may be required. This accuracy can be provided by the high voltage monitoring circuits. However, the user of the power supply usually must specify this requirement before ordering.V. Generating Constant Current SourcesIn many electrostatic applications, a constant current created by corona effects is desirable. This can be accomplished in a number of unique ways. A constant current source can be broadly defined as having a source impedance much larger than the load impedance it is supplying. Schematically it can be shown as in Fig. 7:Practically stated, as R2 changes impedance there is negligible effect on the current through R1. Therefore, R1 and R2 have a constant current. In a single power supply application, this can be accomplished two ways. The first is to provide an external resistor as the current regulating device. The second is to electronically regulate the current using the current feedback control as shown in Fig. 2. In applications where multiple current sources are required, it may not be practical to have multiple power supplies. In this case, multiple resistors can be used to provide an array of current sources. This is typically used where large areas need to be processed with the use of electrostatics. Fig. 8 shows this scheme.VI. ConclusionThis paper presented information useful to electrostatic applications using high voltage power supplies. The high voltage power supply has concerns which differentiate it from conventional power supplies. The designer of high voltage power supplies can be a key resource for the user of electrostatics. Significant control features can be offered by the high voltage power supply. In addition, safety aspects of high voltage use requires important attention. High voltage sources can be lethal. The novice user of high voltage should be educated on the dangers involved. A general guideline for safety practices is found in IEEE standard 510-1983 Recommended Practices for Safety in High Voltages and High Power Testing 4.References:1 C. Scapellati, High Voltage Power Supplies for Analytical Instrumentation, Pittsburgh Conference, March 1995.2 D. Chambers and C. Scapellati , How to Specify Todays High Voltage Power Supplies, Electronic Products Magazine, March 1994.3D. Chambers and C. Scapellati, New High Frequency, High Voltage Power Supplies for Microwave Heating Applications, Proceedings of the 29th Microwave Power Symposium, July 1994.4IEEE Standard 510-1983, IEEE Recommended Practices for Safety In High Voltage and High Power Testing.高压静电电源应用Cliff Scapellati，工程副总裁摘要高压电源供应的关键组成部分是静电应用。各种工业和科学应用的高电压电源供应器以供科学家，工程师，规范和用户的静电。工业生产过程，例如，需要大量的监测作业条件，以便最大限度地扩大产品产量，改善品质，并降低成本。新进展供电技术提供更高水平的监测和过程控制。科学实验还可以影响电力供应的影响。促进效果，如输出精度，稳定，纹波和管理进行了讨论。一。导言使用高电压的科学及工业应用是司空见惯。特别是，静电可用于不同的影响。从广义上说，是研究静电效应所产生的电气费或领域。静电的应用可用于产生运动的材料，无需身体接触，分离材料到元素水平，结合材料，形成均匀的混合物和其他实际和科学用途。根据定义，静电的能力的影响，需要做的工作不同电位两个或两个以上的材料。在大多数情况下，所需的能量，迫使潜在的区别是来自高压电源。这种高电压源可以是一个高压电源应用。今天的高电压电源供应器是固态，高频设计，提供性能和控制无法实现的仅在几年前。显着提高的可靠性，稳定性，控制，减少大小，成本和安全已经实现。通过了解这些改进，用户的高压静电电源的应用中受益。此外，作为独特的要求，高压电源供应器应被理解为他们可以影响到设备，实验，过程或产品。二。高压电源供应器的操作原理图1 一种简化的高压电源一种简化的高压电源如图1。输入电压的来源可能有广泛的电压特性。交流电源50至400Hz在24V到480V是常见的。直流电源从5V至300V也可以找到。关键是用户要了解输入电压的要求，因为这会影响整个系统的使用和设计。监管机构，如美国保险商实验室，加拿大标准协会，国际电工技术委员会及其他具有高度参与任何电路连接到电网。除了主要的逆变电源电路的电源，输入电压源也可以用于辅助电源控制电路和其他辅助电源要求。输入滤波平台提供输入电压源。这种调节通常的形式，整顿和过滤交流渠道，并附加的滤波直流来源。超载保护，EMI，EMC和监控电路也可以找到。输出输入的过滤器通常是直流电压源。这个直流电压提供了能量来源逆变。逆变阶段的直流电源转换为高频交流信号。电力供应中存在许多不同的逆变器拓扑结构。高压电源供应器具有独特的因素，可能会决定逆变器的最佳办法。该逆变器产生高频交流信号是加紧了高压变压器的原因，高频产生是为了提供提供高性能与缩小规模和减少磁存储电容器的纹波。一个变压器具有高加强比例时，高变频器就会被加倍。加强高比率反映了一种寄生电容在主要的高电压互感器，这反映为（Nsec：Npri）第二功能。这种大的寄生电容出现在主要的变压器必须是隔离的逆变器开关设备。如果没有，异常高脉冲电流将会出现在逆变器之中。常见的高电压电源供应器的另一个参数是一种广泛的负荷运作。由于存在高电压，绝缘击穿是司空见惯。该逆变器的稳定性和控制回路的特点，必须负责几乎与任何开路，短路和业务负载相结合的条件。这些问题以及可靠性和成本，必须在高压电源逆变器拓扑结构之中解决。高频逆变器输出的是适用于主要高电压升压变压器。适当的高电压变压器的设计需要大量的理论和实际工程。了解这个有吸引力的设计必须应用材料和过程控制。许多具体的专门知识涉及大量的二级轮流，较高的次级电压。由于这些因素，核心几何，绕组绝缘方法和技术有很大不同，比传统变压器的设计。一些令人关切的领域是：伏特/反过来评级二次线，绝缘层层评级，绝缘材料损耗因数，绕组几何，因为它关注的是寄生电容和次级漏磁，浸渍绝缘漆，以缠绕层，电晕水平和几乎所有其他常规的问题，如热利润率，以及总成本。高电压倍增电路负责整顿和乘法的高电压互感器二次电压。这些电路使用高压二极管和电容器在“电荷泵”电压倍增器的连接。与高电压变压器，高电压倍增器设计需要特定的专门知识。此外，以整顿和乘法，高压电路中使用的过滤器的输出电压，并在监测电压和电流反馈控制。输出阻抗可能故意添加，以防止放电电流从电源的存储电容。这些高电压绝缘部件通常是从地面水平，以防止电弧了。绝缘材料的差别很大，但是典型的材料是：空气，SF6气体，绝缘油，固体胶囊型（RTV，环氧树脂等）。对于一个可靠的高电压设计而言，绝缘材料的选择和过程控制可能是最重要的方面。控制电路使所有的电源一起工作。电路的复杂性可从一个模拟IC到大量的集成电路，甚至一个微处理器控制和监测的所有方面的高压电源。但是，基本的要求，每个控制电路必须满足是精确调节输出电压和电流的负载，输入功率，决定和命令的规定。这是最好的反馈控制回路。图2显示了如何利用反馈信号来调节输出的电压。常规调控电压和电流可通过监测输出电压和电流分别。这是比较理想的（参考）输出信号。差额（错误）之间的反馈和参考将导致改变逆变器控制装置，这将导致改变权力交付输出电路。图2 电源供应控制环此外，电压和电流调节，其他参数可精确调节。控制输出功率很容易完成了XY=Z功能（即VI=W），和比较理想的输出功率范围。事实上，任何变量内发现欧姆定律可以调节（电阻，电压，电流和功率）。此外，最终的工艺参数可调节的影响，如果他们的高压电源（即涂料，流量等）。三。高电压调节必须有一个规范的高电压和/或恒流对于大多数应用中，涉及静电。变化的输出电压或电流可以直接影响最终结果，因此，必须充分理解为一种错误来源。在高压电源供应器，用于项目所需输出电压参数可以消除的一个重大错误来源是使用高度稳定的集成电路。典型规格优于5ppm/C是常规的。同样模拟集成电路（运算放大器，模数和数模转换器，等等）可以消除的一个重要错误来源是慎重挑选你所使用设备。独特的高电压电源供应器还有一个部分，这将是稳定的错误主要来源：高电压反馈分压器。正如图1，高电压反馈分压器由一个电阻分压器网络。这个网络将输出电压足够低的水平来处理的控制电路的问题，稳定在这个网络结果从大阻力的反馈电阻。阻值高于100百万欧姆的电阻是常见的（这是为了降低功耗和减少电路的影响，以及温度变化而产生的自热）。大阻力和高电压等级，需要独特的技术，具体到高电压电阻器。独特的高电压电阻必须“配对”，以低价值的电阻率跟踪，以确保根据温度变化，电压，湿度和时间。此外，高附加值的抵抗的反馈网络是指易感性非常低电流的干扰。可以看出，电流低至110-9放大器将导致“100ppm错误。因此，电晕电流的影响，必须认真加以考虑的设计，电阻和电阻反馈网络。此外，由于许多电阻技术是基于核心或陶瓷基板，压电效应，还必须考虑。它可以证明，振动高压电源在运行期间将实施一个信号，相关的振动频率，在输出的电力供应。四。高压电源需要的辅助功能在许多应用中的高电压，增加控制功能是可能需要的工具。电源设计者必须熟悉的静电应用的最终用户。通过了解应用，电源设计人员可以把重要的职能，以造福于结束进程。一个高压电源典型功能是可以实现一种“电弧识别”的控制，如图3所示。通常情况下，电流感应装置，如电流互感器或电阻插入“低压侧”的高电压输出电路。通常情况下，电弧电流等于：I= （E/R）I=电弧电流安培。E=高压电容器电压。R =输出限制电阻。图3 电弧识别电路电弧电流通常远远大于正常的直流电流额定值的电力供应。这是因为保持阻力限制到最低限度，从而功耗到最低限度。一旦弧事件感觉到，一些功能能够得到执行。“灭弧”一词的特点是电弧终止时电压被消除。图4显示了灭弧功能的框图。图4 灭弧原理如果不想要关闭的第一个弧事件，数字反相器可以添加在所显示的图5。关机或灭弧后会出现预定数目弧线已被识别到。复位时必须使用的低频弧事件不是积累的反相器。例如：如果一分钟内有8个电弧就可以进行一个弧形关机。图5 弧计数电路一个有用的应用识别弧电路能最大限度地施加电压略低于电弧水平。这可以通过遥感，一个弧已经发生和降低电压的一小部分直至电弧停止。电压可以缓慢自动增加（图6）。图6 自动减缓电压框图另一个特点是可以在高电压电源供应器是一种高度准确的电流监测电路。通用应用这一监测功能只能精确到毫安或微安。然而在一些静电应用精度下降到毫微微安倍可能需要。这种精度可提供高电压监控电路，然而用户的电力供应通常必须在订购之前指定这个要求。 五。生成恒流源 在许多静电应用，恒流电晕造成的影响是可取的。这可以在一些独特的方式。恒流源可大致定义为源阻抗远远大于负载阻抗是供应。它显示在图7中。图7 实用恒流源实际上指出，作为R2的阻抗变化的影响是微不足道的，电流通过电阻R1。因此R1和R2有一个恒定电流。在单电源应用，这可以从两方面入手。首先是提供一个外部电阻器的电流调节器。第二是目前的电子监管中使用电流反馈控制如前述图2所示。在应用中经常需要多个电流源，而多个电源可能不够实际。在这种情况下，多个电阻可用于提供一系列的电流源。这通常是大面积使用在需要处理的使用静电。图8显示这项计划。图8 多电流源实现方法六。结论本文介绍了有益的静电应用高压电源。高压电源的关注，区别于传统的电力供应。设计师高电压电源供应器可以是一个关键资源为用户静电。重要的控制功能，可提供的高压电源。此外，高电压使用需要重要关注安全。高电压源可致命，初学者高压的教育应该是所涉及的危险。一般准则的安全做法是在IEEE标准510-1983 “安全高电压，高功率测试的推荐做法 4”。参考文献： 1C.Scapellati，“高压电源分析仪器”，匹兹堡会议，1995年3月。2D.Chambers and C. Scapellati，“如何说明今天的高电压电源供应器”，电子产品杂志，1994年3月。3D.Chambers and C.Scapellati，“新的高频率，高电压电源供应器的微波加热应用”议事第29次微波功率研讨会，1994年7月。4IEEE标准510-1983,符合IEEE安全的高电压和高功率测试建议操作15
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