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实验二传导性电磁干扰（EMI）噪声测试系统一实验目的1 了解传导电磁干扰基本概念2 熟悉传导电磁干扰诊断与抑制基本原理3 掌握电磁兼容基本实验仪器使用二实验设备•频谱分析仪GSP-827•线阻抗稳定网络LISN•分离网络DN•开关电源（型号为KR0960AA 24V 40A）•EMI滤波器•负载电阻盘•线缆•50Ω匹配阻抗三实验内容及步骤1、传导性电磁干扰诊断与抑制原理图图1是传导性电磁干扰诊断与抑制系统示意图。
在主测量装置的输出端获取被测设备（EUT）的EMI噪声后，输入到共模CM/差模DM分离网络进行模态分离。
而后由诊断软件对从频谱分析仪传送到计算机上的信号进行处理。
该智能系统不仅可利用硬件提供独立的共模及差模分量，同时也利用软件为滤波器设计提供了有益的诊断信息。
本实验只要求学生利用频谱分析仪检测到噪声信号，及了解加入滤波器后噪声明显降低，满足EMC标准。
图1 传导性EMI智能测试系统示意图2 、实物接线图及各部分功能介绍将开关电源接一组（3个）500W，5Ω并联的电阻盘用作被测设备即噪声源，在测试系统中加入自制的功率滤波器以此作为我们全智能测试系统的检测对象。
该系统由由线阻抗稳定网络LISN，AC/DC，24V 960W直流输出开关电源接一组（3个）500W，5Ω并联的电阻盘，由功率合成器combiner构成的噪声分离网络DN及GSP-827频谱分析仪构成的EMI噪声智能诊断系统，由EMI滤波器构成噪声抑制系统，供电电源来用单相三线220V交流工频电源。
实验装置如图2所示。
图2 以开关电源拖带阻性负载为被测设备的实验装置图⑴线阻抗稳定网络LISN：目前国际标准进行的传导性电磁干扰测量系采用线阻抗稳定网络LISN，，其核心是通过电感、电容和标准50 阻抗构成的测试网络（前一节已做介绍），作为获得被测设备EUT所产生的传导干扰信号的接受器。
⑵噪声分离网络DN：，LISN只能测量到传导性EMI噪声的混合信号而不能从中检测出CM 和DM分量，但EMI滤波器设计却分为共模和差模滤波器两种。
技术难点1：EMI问题探讨(一)、在灯具闭态条件下，EMI-传导测试中150K~2M频段有频点超标，一般原因为闭态取电电路的差模噪声较大。
针对这类现象，可尝试如下方法进行改善：(1).若通过增加X电容抑制差模噪声来优化EMI-传导性能，则X电容会导致闭态待机电流增大，对低功耗单火开关方案来说，该对策会恶化”鬼火”现象，一般不建议采取该对策；(2).建议优化缩短火线L、灯线L1输入端到整流桥之前的PCB layout走线，尽量避免输入端交叉走线；如下图粗红色输入走线所示；(3).建议闭态取电电路中采用桥堆作为输入整流器件，缩短整流环路，尽量避免使用分立二极管搭建；(4).闭态取电电路中输入大电容电路可预留LC或π型滤波电路作为EMI对策。
设计注意点：此对策器件选型、参数可能会对待机功耗有影响，调试过程中须留意待机电流的变化；(二)、在灯具开态条件下，开态取电电路选取合适的GATE驱动电阻。
此GATE为低频开关信号，驱动电阻R4建议选取20~30K，让MOSFET开启更缓。
若R4不够大或MOSFET的结电容偏小，EMI会比较差，可根据EMI情况调整。
下图为驱动电阻R4电路图示以及不同驱动电阻R4阻值传导测试对比结果：驱动电阻R4电路图示不同驱动电阻R4阻值传导测试对比技术难点2：支持大功率单火取电开关的探索随着智能家居产品的多元化、多样化，市面上出现带触摸屏、语音交互、音乐、网关等更多功能的智能开关产品，这类智能开关产品的功耗都在5V/0.5A 以上，且基本上都是采用零火线供电方案，传统单火取电方案不能满足需求。
为满足这类产品可直接应用在单火线布线场景中，需要开发一款可以支持大功率取电的单火开关。
这类产品应用在单火场景会碰到的技术难点：无论在灯具关态还是开态，其功耗都在5V/0.5A以上，这对单火取电技术提出了更高的要求。
在此列举其中一种支持大功率单火取电的解决思路，其电路框架示意图如下：在灯具两端并联设计一款分流电路，配合单火智能开关的取电电路输出不小于5V/0.5A功率给智能开关系统电路供电。
《EMI对症分析-EMI整改》第一篇：emi对症分析-emi整改1mhz以内----以差模干扰为主1.增大x电容量；2.添加差模电感；3.小功率电源可采用pi型滤波器处理（建议靠近变压器的电解电容可选用较大些）。
1mhz---5mhz---差模共模混合，采用输入端并联一系列x电容来滤除差摸干扰并分析出是哪种干扰超标并以解决，1.对于差模干扰超标可调整x电容量，添加差模电感器，调差模电感量;2.对于共模干扰超标可添加共模电感，选用合理的电感量来抑制；3.也可改变整流二极管特性来处理一对快速二极管如fr107一对普通整流二极管1n4007。
5m---以上以共摸干扰为主，采用抑制共摸的方法。
对于外壳接地的，在地线上用一个磁环串绕2-3圈会对10mhz 以上干扰有较大的衰减作用;可选择紧贴变压器的铁芯粘铜箔，铜箔闭环.处理后端输出整流管的吸收电路和初级大电路并联电容的大小。
对于20--30mhz，1.对于一类产品可以采用调整对地y2电容量或改变y2电容位置；2.调整一二次侧间的y1电容位置及参数值；3.在变压器外面包铜箔；变压器最里层加屏蔽层；调整变压器的各绕组的排布。
4.改变pcblayout；5.输出线前面接一个双线并绕的小共模电感；6.在输出整流管两端并联rc滤波器且调整合理的参数；7.在变压器与mosfet之间加beadcore；8.在变压器的输入电压脚加一个小电容。
9.可以用增大mos驱动电阻.30---50mhz普遍是mos管高速开通关断引起，1.可以用增大mos驱动电阻；2.rcd缓冲电路采用1n4007慢管；3.vcc供电电压用1n4007慢管来解决；4.或者输出线前端串接一个双线并绕的小共模电感；5.在mosfet的d-s脚并联一个小吸收电路；6.在变压器与mosfet之间加beadcore；7.在变压器的输入电压脚加一个小电容；8.pcb心layout时大电解电容，变压器，mos构成的电路环尽可能的小；9.变压器，输出二极管，输出平波电解电容构成的电路环尽可能的小。
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theyclock.yInytheory,ytheypresenceyofythey commonymodeychokeyshouldyforceycurrenty toyreturnythroughytheyreturnywire,ytheyoney thatypassesythroughytheycommonymodey choke,yinsteadyofythroughytheyreturnyplane.y Evenyifytheyreturnyplaneywasyinductiveybecauseyofytheypresenceyofyanyopeningysuchy asyayslit,ylittleyvoltageywouldybeydroppedy acrossytheyreturnyplaneysimplyybecauseythey RFycurrentydoesynotypassythroughyit.y WeyusedytheycircuityofyFigurey6.yTheyy returnyplaneywasygapedyasyinyFigurey4.yy Aytwistedypairyconsistingyofy24yAWGy magnetywireywasypassedythroughytwoyy Fair-Ritey2643000801yNo.y43ytypeyferritey beadsy1y1/2ytimesyandywasythenyconnectedy theyclockyandytheyload.yTheyreturnywireywasy connectedytoytheygroundyplaneyimmediatelyy adjacentytoytheyclockyandytheyload.yEmissionsyfellydramaticallyyaty125yMHz,yytoy38.7ydBuv/myaty10ymeters.yFigure 5Figure 6: One unorthodox method of suppressing radiation is to use acommon mode choke in the drive circuit�Test Conditions Figure Measured Emissions (dBuV/m at 10m)Predicted Emissions (dBuV/m at 10m)Solid Return Plane Figure 2 39.4 40.2 Slotted Return Plane Figure 4 59.8 63.0 Holed Return PlaneFigure 5 40.2 ~ 41 Slotted Return Plane with CM Choke Figure 6 38.7 -Solid Return Plane with CM Choke N/A 32.7 -Clock Running Alone with No Wires AttachedN/A29.7-Table 1: Radiation detected at 125 MHz is shown under varying conditions�EMI: Why Digital Devices RadiateEmissionsywereythenymeasuredyusingyay circuitythatyemployedybothyaycommonymodey choke,yasyshownyinyFigurey6,yandytheysolidy groundyplaneyofyFigurey2.yEmissionsyfelly onceyagain,ythisytimeytoy32.7ydBuV/m.yy Asyayfinalytest,ytheyconnectionybetweenythey clockyandytheyloadywasyremovedysoythatythey clockyoscillatorycouldyrunybyyitselfywithouty anyywiresyattached.yAty125yMHzytheyclocky oscillator,yoperatingyaloneyandyfedypowery throughysolidyV+yandyV-yplanes,yproducedy 29.7ydBuv/myofyemissions,yonlyy3ydBylessy thanytheyemissionsyproducedybyytheyuseyofyay combinationyofyaycommonymodeychokeyandy aysolidyreturnyplane.yDatayisysummarizedyy inyTabley1.ySoyfar,ysoygood.yTheoryyworksywellyatyy125yMHz.yButytheoryydoesynotyworkywellyaty theyninthyharmonic,y225yMHzy(Tabley2).yy Inyfact,ywhatyisyremarkableyaboutythey 225yMHzydatayisythatyitywasyseeminglyy unaffectedybyyanythingythatyweydid.yThey logicalyconclusionytoybeydrawnywasythatyemissionsyatytheyhigheryharmonicsywereyFigure 7: Variously called I dd Delta, Idd Noise or “Shoot Through” current, aspike in supply current drawn occurs as a MOS gate changes state�notysoymuchydueytoycurrentyonytheydrivenywireybutywerey dueytoysomeyinternalymechanismyinytheyintegratedycircuitsy themselves.yTheyintegratedycircuitsyusedywereyofytheyMOSyfamily.yFigurey7y showsytheybasicystructureyofyayMOSydevice.yPychannelyandyy Nychannelydevicesyserveyasyswitchesyalternatelyyconnectingy theyoutputytoyV+yandyV-,ydependingyonytheyinputyvoltage.yVeryy littleycurrentyflowsyfromyV+ytoyV-ywhenyaygateyisyeitheryinyitsy highyorylowystate.yForyexample,ywhenytheyinputyofyaygateyisy inyitsyhighystate,ytheyNychannelyFETyisyturnedyonyconnectingy theyoutputytoyV-.yTheyPychannelydeviceyisyinyitsyoffystateyandy presentsyayveryyhighyimpedanceybetweenyV+yandytheyoutput.y Therefore,ylittleycurrentyflowsybetweenyV+yandyV-.yTheysamey situationyisytrueyinyreverseywhenyinputyisylowyandytheyoutputy isyhigh.yInytheytransitionyregion,yhowever,ycurrentydoesyflowy fromyV+ytoyV-.yThisycurrentyisyayfunctionyofyinputyvoltage,yandy isyshownyinyFigurey7.yItypeaksysomewhereyinytheymiddleyofythey inputyvoltageyrange,yandyisyknownyasy“I ydd yDelta,”y“I ydd yNoise”y orysometimesyasy“shootythrough”ycurrent.yTheyeffectyofyI ydd yDeltayisytoyproduceyay veryybriefycurrentypulseyeveryytimeythey gateychangesystate.yTheynetyresultyisyay currentypulseyonytheysupplyyplanesyofy approximatelyy1ymilliampypeakyandyabouty 1ynanosecondyinywidthyeachytimeyaytypicaly 74HC02ygateyswitches.yUnfortunately,ytheyamountyofyradiationywey canyexpectydueytoyI ydd yDeltaycanybeydifficulty toypredict.yForyoneything,ymanufacturersy rarelyyciteyI ydd yDeltayinytheirydataysheets.y Foryanother,yI ydd yDeltayisyhighlyyvariable.y Amongyotherythingsyityisyayfunctionyofythey supplyyvoltage,yvaryingyasyayfunctionyofyy V cc ytoythey2.2ypower.y[7].Figurey8yshowsyhowythisycurrentypulseyturnsy intoyayvoltageyacrossytheyreturnyplane.yy I ydd yNoiseycurrentymostlyypassesythroughy anyybypassycapacitoryimmediatelyyadjacenty toytheyintegratedycircuit.yHowever,ythey impedanceyofythatycapacitoryisyfinite,yandy someyofytheycurrentyisyfedybackythroughythey supplyyplanes.yThisycreatesyaynoiseyvoltagey dueytoytheyimpedanceyofytheyreturnyplane.yTest Conditions Figure Measured Emissions (dBuV/m at 10m) Solid Return Plane Figure 2 50.2 Slotted Return Plane Figure 4 51.2 Holed Return Plane Figure 5 50.1 Slotted Return Plane with CM Choke Figure 6 49.6 Solid Return Plane with CM ChokeN/A50.1Table 2: Radiation detected at 225 MHz under varying conditions is shown� Unlike the radiation detected at 125 MHz, the changing conditions did notaffect the radiation at 225 MHz significantly�Figure 8: The spike in supply current caused by I dd Delta creates a current flowthrough the return plane� Frequency (MHz)Circuit of Figure 4Circuit of Figure 9bReduction (dB)75 41.3 27.3 14.0 125 59.8 31.2 28.6 175 53.4 34.3 19.1 225 51.2 33.6 17.6 275 33.8 27.8 6.0 325 48.4 22.7 25.7 375 48.4 <20 >28.4 425 39.4 <20 >19.4 475 37.3 <20 >17.3 52531.7<20>11.7Table 3: Reductions in Emissions (dB/uV at 10m)Figure 9: A small pi filter on the supply of the 25 MHz clock as shown in (b) dramatically reduced radiation at 225 MHz� Even a short length of wire as shown in (c) significantly reduced radiation by forming an LC filter�The filter works by reducing IDelta�ddAs mentioned, our test circuit already had wafer type capacitors placed immediately below the ICs. So as a further experiment, we isolated the V+ pin (pin 14 on both devices) from the V+ plane. A wire was connected as shown in Figure 9c. Although identical on a schematic, this configuration provided some filtering because of the wire’s inductance. Test results show a reduction of 9 dB at 225 MHz. The next step was to add a second bypass capacitor as shown in Figure 9b (a 1000 picofarad surface mount multilayer type) and to replace the wire with a surface mount device designed to increase series impedance over a wide frequency range.A TDK MMZ2012S301 was chosen which, according to the manufacturer’s data sheet, exhibits an impedance of greater than 300 ohms at the frequencies of interest. An additional reduction of more than 19 dB was noted.Table 3 demonstrates the results of our efforts. Note that improvement was achieved without using any filtering near our “I/O” (telescoping elements) or shielding. nREFERENCES1. F. Leferink, “Inductance Calculations: Methods AndEquations,” 1995 IEEE International Symposium onElectromagnetic Compatibility, Page 16.2. D. Hockanson, J. Drewniak, T. Hubing, T. Van Doren, F.Shu, C. Lam, L. Rubin, “Quantifying EMI Resulting from Finite-Impedance Reference Planes,” IEEE Transactions on Electromagnetic Compatibility, Nov. 1997, Page 286.3. G. Dash et al, “Computational Methods Aid inUnderstanding Antennas,” Conformity Annual 2001,Page 126.4. R. Hill, T. Van Doren, T. Hubing, J. Drewniak, and F.Gisin, “Common Mode Currents Induced On WiresAttached To Multilayered Printed Wire Boards WithSegmented Ground Planes,” 1994 IEEE InternationalSymposium on Electromagnetic Compatibility, Page 116.5. G. Dash et al, “Designing for Compliance. We Put Theoryto the Test,” Conformity, March 1998, Page 10.6. F. J. Tilley, “Reducing Radiated Emissions on High SpeedSignal Lines Using Common Mode Choke Coils,” IEEE Symposium on Electromagnetic Compatibility, 1995.7. High Speed CMOS Designer’s Guide, Signetics/Philips,Feb. 1986, Page 2-18.Glen Dash is the author of numerous papers on electromagnetics. He was educated at MIT and was the founder of several companies dedicated to helping companies achieve regulatory compliance. Currently he operates theGlen Dash Foundation which uses ground penetrating radarto map archaeological sites, principally in Egypt.Copyright Ampyx LLC。
EMI滤波器的应用及选择指南一、EMI滤波器的电路结构形式（右图所示）：1、C型滤波器C型滤波器由三端电容和穿心电容构成，适合于抑制高频。
C型滤波器两端均可视为低阻抗，接高阻抗源和负载。
2、L型滤波器由一个电感器和一个电容器组成。
这种滤波器可以提供高的输入阻抗，也可提供低的输入阻抗，取决于电路的安装方向。
LT电路适用于高阻抗负载，低阻抗源的情况。
LB电路适用于低阻抗负载，高阻抗源的情况。
3、π型滤波器π型滤波器由一个电感器两个电容器构成。
它的输入端和输出端都呈低阻抗性，因为元件比L型或C型多，故抑制性能要好的多。
但在开关电路中有时会出现“振铃”现象。
4、带瞬变抑制器的π型滤波器这种π型滤波器在其输入端增加了一个瞬变抑制器，它具有较好的高频抑制性能，同时可以防止电压尖峰。
5、T型滤波器这种滤波器包括两个电感器和一个电容器，它的两端都是高阻抗，其插入损耗性能和π型滤波器相似。
但它不易出现“振铃”现象，可用在开关电路中。
6、双T型滤波器（多级滤波器）多级滤波器是为源和负载都为低阻抗的电路设计的高性能滤波器，它们也可用在要求高插入损耗的其他情况。
在滤波器的输入端用一个电感器，有利于与美军标MIL-STD-461D（国军标GJB-151A）的测试装置匹配。
二、各种滤波电路的衰减特性：不同的滤波电路有着不同的滤波特性（见右图）。
一般而言，C 型电路的滤波衰减曲线较平坦，没有明显的拐点，适用于大多数电子设备；L 型电路Pi 型电路和T 型电路的滤波衰减曲线较C 型电路拐点明显，适用于抑制的干扰信号与有用信号频率接近的的场合。
但当工作频率为方波时，要注意这些电路的感性和容性器件的量值要选用恰当，避免一味追求滤波衰减性能，而把有用信号的波形部分衰减，导致设备工作反而不正常。
各种滤波电路滤波特性图一、 E MI 感性和容性器件的选择：滤波电容EMI 滤波器所用电容一般为穿芯式陶瓷电容，穿芯式的结构可有效防止高频信号在输入输出端之间直接耦合，且寄生电感小自谐振频率较高，这种同轴性的、低通高阻的设计组合，在1GHz 的频率范围内，可以提供高效的EMI 抑制。
批准： 日期： 第 1 页 共 3 页 连接仪器电源及被测负载电源的连接线；将待测样品的负载按要求接入。
分钟稳定后连接测试仪器数据线；当电脑通讯正常，打开电，打开测试界面。
测试完毕后，保存测试数据记录，关闭仪器及被测物电源。
电源端子骚扰电压测试： 线对电网的骚扰电压应不超过GB17743-2007表2a 限值；接收机、ENV216 人工电源网络（如下图）； 连接人工电源网络后，连接接收机与人工电源网络的数据线； 键新建文件，然后点击Configure 配置，在limit （QP ）选GB17743-2007 QP ，limit(AVG)选择（CE ）GB17743-2007 AVG ，Antenna Conduction 键后点击SET 即可完成测试设定； Trace 追踪键，则接收机开始扫描测试； 11 10 12 13 14 15 16 17。
