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1、Equipment for switching power supply testing File:AC003.doc Page 1 of 11 Date:28-Dec-2001 1.引言/Introduction 此文件描述一般开关电源供应器的测试仪器及其特性。This document describes general equipment used in switching power supply testing and their characteristics.-示波器/Oscilloscope.-电压探头/Voltage probe.-交流电流探头/AC current prob
2、e.-数字式电压表/DVM.-有效值表/RMS meter.-功率表/Power meter.-温度测量表/Temperature measurement.-电子负载/Electronic load.-交流电源/AC source.-台式直流电源/Bench top DC power supply.2.示波器/Oscilloscope 是用来显示一个或多个随时间快速变化的电量的设备。这个电量通常是指开关电源 测试中的电压或电流。大多数示波器是用 CRT(阴极射线管)显示的数字存储型示 波器也有用液晶显示的。An instrument that produce a visible image o
3、f one or more rapidly varying electrical quantities with respect to time.The quantities are usually a voltage or current in switching power supply testing.The most usual type of oscilloscope use CRT(cathode ray tube)display,LCD display is also available for digital storage type.2.1 示波器类型/Type of osc
4、illoscope 模拟示波器不能存储。水平扫描是在示波器内部产生的(除用 XY 模式)。射线 束在垂直方向的位置随 CH1 或 CH2 的输入信号而变化。Analog scope:No storage.The horizontal sweep is generated internally in the oscilloscope(except in XY mode).The vertical position of beam on the display will vary according the input signal to VERT(CH1 or CH2).数字存储示波器矢量显示(
5、Tektronix 2232)对于非存储模式类似仿真示波 器。对于存储模式首先输入信号经模/数转换并存储在存储器中存储后的 信号再经数/模转换然后调整光束的垂直位置。这种类型的示波器现在已经逐 步被淘汰。Digital storage scope,vector display,(Tektronix 2232):In non-store mode,this kind of scope is same as an analog scope.In storage mode,the input signal to VERT is first converted with A/D and stored
6、in memory,then the content of the memory will be converted back to analog signal with D/A and modulate the vertical position of the beam.This type of scope is phasing out now.数字存储示波器监控显示(Tektronix TDS3012)这种显示是监控显示(类似计 算机显示)。首先输入信号必须由模/数转换并存储在存储器中。这类示波器没 有类似仿真示波器的功能。Equipment for switching power sup
7、ply testing File:AC003.doc Page 2 of 11 Date:28-Dec-2001 Digital storage scope,monitor display(Tektronix TDS3012):The display is a monitor display(similar to computer display).The input signal must be converted with A/D and stored in memory first.This kind of scope cannot function as an analog scope
8、.2.2 重要的控制/Important control 2.2.1 垂直/Vertical.-垂直增益(伏/格)/Vertical gain(V/div).-垂直位置/Vertical position-直流耦合/DC coupling-交流耦合/AC coupling 2.2.2 水平/Horizontal-时间/格/Time/div.-水平位置/Horizontal position.2.2.3 触发/Trigger 为了使波形的起点在每个屏幕的位置相同使用触发是必要的否则不能显示稳 定的波形。Tigger is required so that the start point of t
9、he waveform on every screen is the same,otherwise no stable waveform can be seen on the display.-源CH1,CH2,Line 等。/Source:CH1,CH2,Line,Ext.-电平/Level.-沿+-。/Slope:+-.-偶合直流交流高频滤除 TV。/Coupling:DC,AC,HF Rej,TV.-触发延迟时间。/Trigger hold time.2.3 使用注意事项/Precaution in use.2.3.1接地问题/Earthing problem.通常示波器的地是与安全地相
10、连而测试电路中的地对于对安全地来说是必 需浮动的。In general,the scope ground is connected to safety earth,while the ground of circuit under test shall be floating with respect to safety earth.示波器的地不能接到任何高压变动的一端。Scope ground shall not be connected to any node with high voltage swing.测量两个变动端之间的电压波形(例如前置转换整流器)必须用相减的方法 例如 CH1-
11、CH2。To measure the voltage waveform across 2 swinging node(e.g.forward converter rectifier),differential method shall be used,i.e.CH1-CH2.如果测试电路是浮动的示波器的地也可以接到除地以外的其它直流电平处 Equipment for switching power supply testing File:AC003.doc Page 3 of 11 Date:28-Dec-2001 率表温度测量表电子负载交流电源台式直流电源示波器是用来显示一个或多个随时间快速
12、变化的电量的设备这个电量通常是指开关电源测试中的电压或电流大多数示波器是用阴极射线管显示的数字存储型示波器也有用液晶显示的示而变化数字存储示波器矢量显示对于非存储模式类似仿真示波器对于存储模式首先输入信号经模数转换并存储在存储器中存储后的信号再经数模转换然后调整束的垂直位置这种类型的示波器现在已经逐步被淘汰数字存储示波器监控真示波器的功能重要的控制垂直垂直增益伏格垂直位置直流耦合交流耦合水平时间格水平位置触发为了使波形的起点在每个屏幕的位置相同使用触发是必要的否则不能显示稳定的波形源等电平沿偶合直流交流高频滤除触发延迟时间而两个探头的地不可以接到两个非隔离的不同直流电平的地方。Scope gr
13、ound may be connected to other DC level in the circuit other than ground provided the circuit under test is floating.However,2 probe ground must not be connected to 2 different non-isolated DC level.2.3.2数字示波器问题/Digital scope problem 数字示波器不是很适合测量纹波。模拟示波器的亮度调节可以让你区分 100HZ 的纹波开关纹波及尖峰。对于数字示波器如果尖峰很高在取样模
14、式中尖 峰会被显示成随机幅度的尖峰。在峰值检测模式中其它纹波成份会被掩盖。Digital oscilloscope is not very suitable for ripple measurement.The intensity modulation in analog scope let you distinguish 100Hz ripple,switching ripple,and spike.In digital scope,if the spike is high:In sample acquisition mode,it will be shown as random ampli
15、tude spikes.In peak-detect mode,it will mask all other ripple component.TDS340 每个屏幕取 500 个样。很多细节会在取样模式中丢失。对于有尖峰的波 形尖峰的幅度是随机的并且在连波中会不同的。TDS340 captures 500 samples per screen.Many details may be lost in sample acquisition mode.For waveform with spkies,the magnitude of spike will be random and differe
16、nt on consecutive waveform.TDS3012/3014每个屏幕取样 10,000个。TDS340 中对于有尖峰的波形尖峰的 幅度会更加稳定。如果尖峰幅度依然变化尖峰的宽度必定很窄水平时间/格 必须设定很快才能得到其稳定的尖峰幅度。TDS3012/3014 capture 10,000 samples per screen.For waveform with spikes,the magnitude of spike will be much more consistent than with TDS340.If the spike amplitude is still
17、varying between waveforms,then the spike width must be very narrow,the horizontal time/div shall be set faster to obtain consistent spike amplitude.3.电压探头/Voltage probe 3.1 电压探头的类型/Type of voltage probe X1 探头没有衰减输入阻抗跟示波器输入阻抗一样(通常是 1 兆欧)。由于对测 试电路有很大的负载影响所以很少使用这种探头。X1 probe:no attenuation,input impeda
18、nce follow that of scope input impedance(usually 1 Mohm).This type of probe is seldom used because of heavy loading effect on circuit under test.X10 探头衰减 10 倍当使用的示波器的输入阻抗为 1 兆欧其输入阻抗为 10兆 欧输入电容大约为 13pF。对直流和低频输入电压的峰值上限为 600 伏。X10 probe:attenuation of 10:1,input impedance 10 Mohm when used with a scope
19、 of 1 Mohm input impedance,input capacitance around 13p.F Input voltage peak limited to 600V for DC and low frequency.X100探头例如 Tektronix P6009衰减 100倍当使用的示波器的输入 阻抗为 1 兆欧其输入阻抗为 10 兆欧输入电容约为 2.5pF。对直流和低频输入电压的峰 值上限为 1500 伏。Equipment for switching power supply testing File:AC003.doc Page 4 of 11 Date:28-D
20、ec-2001 X100 probe:e.g.Tektronix P6009,attenuation of 100:1,input impedance 10Mohm when used with a scope of 1 Mohm input impedance,input capacitacne 2.5.p IFnput 率表温度测量表电子负载交流电源台式直流电源示波器是用来显示一个或多个随时间快速变化的电量的设备这个电量通常是指开关电源测试中的电压或电流大多数示波器是用阴极射线管显示的数字存储型示波器也有用液晶显示的示而变化数字存储示波器矢量显示对于非存储模式类似仿真示波器对于存储模式首先
21、输入信号经模数转换并存储在存储器中存储后的信号再经数模转换然后调整束的垂直位置这种类型的示波器现在已经逐步被淘汰数字存储示波器监控真示波器的功能重要的控制垂直垂直增益伏格垂直位置直流耦合交流耦合水平时间格水平位置触发为了使波形的起点在每个屏幕的位置相同使用触发是必要的否则不能显示稳定的波形源等电平沿偶合直流交流高频滤除触发延迟时间voltage limited to 1500V for DC and low frequency.3.2 使用注意事项/Precaution in use 无论何时 X10和 X100的探头与示波器组合改变都需要用示波器上的方波校正 探头的高频响应。Whenever
22、 a scope/probe combination for X10 and X100 probe changes.Recalibrate the high frequency response of the probe with the square wave on the scope.对于低频和逻辑测量如有任何从示波器的地到电路地的连接探头的地就可 以不接。For low frequency and logic measurement,any ground connection from scope ground to circuit ground is OK,the probe grou
23、nd may be left open.对于高频或低幅值测量探头的地应接到测试电路中的适当位置。For high frequency,or low amplitude measurement,probe ground shall be connected to appropriate points in the circuit under test.探头的电容会对测试电路有影响例如当测量振荡器的时候电容会降低振荡 频率。The probe capacitance may affect the circuit being measured,e.g.the capacitance may lowe
24、r the oscillating frequency when measuring an oscillator.探头不要接触热的部位例如 TO-220 金属板或正在焊锡中的零件脚。Do not clip probe to hot parts,e.g TO-220 metal plate,or components lead that are being soldered.4.交流电流探头/AC Current probe 交流电流探头是利用电流变压器的原理来测试电流的它的中心部分可以打开和 卡紧在有电流流过的导线上。电压会按照某个比率产生在端口。只有高于某些频率 的交流电流才能被准确的测到。
25、AC current probe act as a current transformer which the core can be opened and clamped on a current carrying conductor.A voltage will be developed at the termination at certain ratio.Only AC current above certain frequency can be measured accurately.4.1 使用注意事项/Precaution in use 交流电流探头不能用来测量低频电流波形。(例
26、如 Tektronix P6021 10mA/mV 文 件 3dB 的截止频率点为 120Hz 2mA/mV 档为 450Hz)。AC current probe shall not be used to measure low freqeuncy current wavform.(e.g.Tektronix P6021,3dB point is 120Hz at 10mA/m,V 450Hz at 2mA/mV).对于 P6021电流波形峰值不能超过 15Amp。Current waveform shall not exceed 15 Amp peak for P6021.5.数字式电压表/
27、DVM 5.1 直流电压测量/DC voltage measurement Equipment for switching power supply testing File:AC003.doc Page 5 of 11 Date:28-Dec-2001 基本功能是将直流电压转换成容易读出的数字显示。根据精密的需求分为三位 半四位半五位半数字显示或更多位显示的。The basic function is to convert a DC voltage into a digital display which can be read easily.Depending on accuracy re
28、quired,3 1/2 digit,4 1/2 digit,5 1/2 digit display or more is available.率表温度测量表电子负载交流电源台式直流电源示波器是用来显示一个或多个随时间快速变化的电量的设备这个电量通常是指开关电源测试中的电压或电流大多数示波器是用阴极射线管显示的数字存储型示波器也有用液晶显示的示而变化数字存储示波器矢量显示对于非存储模式类似仿真示波器对于存储模式首先输入信号经模数转换并存储在存储器中存储后的信号再经数模转换然后调整束的垂直位置这种类型的示波器现在已经逐步被淘汰数字存储示波器监控真示波器的功能重要的控制垂直垂直增益伏格垂直位置直流
29、耦合交流耦合水平时间格水平位置触发为了使波形的起点在每个屏幕的位置相同使用触发是必要的否则不能显示稳定的波形源等电平沿偶合直流交流高频滤除触发延迟时间有相对较高的准确性例如三位半数字显示精确度 0.1%四位半的为 0.03%。Accuracy is relatively high,e.g.0.1%for 3 1/2 digit,0.03%for 4 1/2 digit.数字式电压表通常有 10兆欧的输入阻抗。当测量高阻抗电路时可能会有影响。DVM usually got an input impedance of 10 Mohm.There may be loading effect when
30、 measuring high impedance circuit.5.2 直流电流测量/DC current measurement 对于直流电流测量在电流通道串联一电流分流器将电流转换成直流电压信号。For DC current measurement,a current shunt is place in series in the current path and convert the current to a DC voltage signal.5.3 交流测量/AC measurement 对于交流电压测量利用有效值转换电路或精密整流器电路将交流信号转换成 直流电压。For AC
31、 voltage measurement,an rms converter circuit or a precision rectifier circuit convert the AC signal into a DC voltage.有两种类型的交流电压表。一种是真正的有效值响应例如 GDM8145。另一种 是平均值响应但显示为正弦波的有效值例如 GDM8135。这种平均值响应特 性不适合于开关电源稳压器的交流输入电流的测量因为电流并非是正弦波。There are 2 kind of AC voltmeter.One is true RMS responding,e.g.GDM8145.T
32、he other is average responding but calibrated to display RMS reading for sine wave only,e.g.GDM8135,this average responding characteristic is not suitable for measurement of switching power supply input AC current which is not sinusoidal.通常一般用途的 DVM 表只有测量从 50Hz到 10KHz 的交流较为精确。Usually AC measurement
33、is accurate from 50 Hz to 10 KHz only for general purpose DVM.5.4 电阻测量/Resistance measurement 对于电阻的测量数字式电压表会送出一个小电流并且测量表笔两端的电压 因此电阻的引脚电阻也被包含在内。对于大阻值电阻其引脚电阻是可忽略的。For resistance measurement,the DVM will pump out a small current and measure the voltage across the 2 terminals,so the resistance of the 2
34、lead is included.For high resistance measurement,the lead resistance is negligible.数字式电压表在测量低于 20 奥姆的电阻时会因为引脚的电阻而使测量不准 确。除非它是一个四线奥姆表。DVM is not accurate in measuring resistance below 20 ohm due to the lead resistance,Equipment for switching power supply testing File:AC003.doc Page 6 of 11 Date:28-De
35、c-2001 unless it is a 4 wired ohm meter.低阻值的测量也可以通过流过的电流并且用 Kelvin 接触法测量电压用电压 除以电流的方法来计算阻值。Low resistance measurement can also be done by pumping a current through the resistor and measure the voltage across it with Kelvin contact method,then use V/I to calculate the resistance.5.5 使用注意事项/Precaution
36、 in use 通常红黑端对地来说是浮动的。然而在黑端与地之间有高电容。因此黑端不 能接在有变动高电压的点上。Usually both the red and black terminal are floating with respect to earth.However,there is high capacitance between black terminal and earth.So the black terminal shall 率表温度测量表电子负载交流电源台式直流电源示波器是用来显示一个或多个随时间快速变化的电量的设备这个电量通常是指开关电源测试中的电压或电流大多数示波器是
37、用阴极射线管显示的数字存储型示波器也有用液晶显示的示而变化数字存储示波器矢量显示对于非存储模式类似仿真示波器对于存储模式首先输入信号经模数转换并存储在存储器中存储后的信号再经数模转换然后调整束的垂直位置这种类型的示波器现在已经逐步被淘汰数字存储示波器监控真示波器的功能重要的控制垂直垂直增益伏格垂直位置直流耦合交流耦合水平时间格水平位置触发为了使波形的起点在每个屏幕的位置相同使用触发是必要的否则不能显示稳定的波形源等电平沿偶合直流交流高频滤除触发延迟时间not be connected to nodes with high voltage swing.最大电压限额的处理例如 GDM8135。Ta
38、ke care of maximum voltage limit,e.g.GDM8135.直流电压最大为 1200V。/DC voltage:1200 V maximum.交流电压最大为 1000V。/AC voltage:1000 V maximum.共模电压峰值为 1200V 或者最大有效值为 500V。(不要将黑端接到和安全地超 过 500Vrms 的电压上)Common mode voltage:1200 V peak or 500 Vrms maximum.(do not connect the black terminal to any voltage higher than 50
39、0Vrms with respect to safety earth.)6.有效值表/RMS meter 有效值表用来测量高频的交流电压(10KHz)在该频率上普通数字式电压表会不 准确。RMS meter is used for measuring high frequency AC voltage(10KHz)which ordinary DVM becomes inaccurate.6.1 原理/Theory 热效应有效值-直流转换器频率响应可高达 10MHz。Thermal RMS-DC converter,frequency response can be very high,up
40、to 10MHz.模拟计算方法利用对数-平方-反对数。频率响应较差这种类型的 IC 较为普 遍。Analog calculation method,use log-square-antilog.Frequency response is not so good.This type of IC is more common.6.2 使用注意事项/Precaution in use 对于 Fluke 8921A红黑两端对大地来说是浮动的。然而黑端与地之间有很大 电容。因此黑端不能接到有变动高电压的一端。For Fluke 8921A,both the red and black terminal
41、are floating with respect to earth.However,there is high capacitance between black terminal and earth.So the black Equipment for switching power supply testing File:AC003.doc Page 7 of 11 Date:28-Dec-2001 terminal shall not be connected to nodes with high voltage swing.最大电压限额的处理例如 Fluke 8921A。Take c
42、are of maximum voltage limit,e.g.Fluke 8921A.-差模电压最大为 700Vrms。/Differential voltage:700 Vrms maximum.-共模电压最大为 500Vrms。/Common mode voltage:500 Vrms maximum.适合有效值表测量的范围/Suitable for true RMS measurement from,-当选择交流+直流从直流到 20MHz(3-5%的误差)。/DC to 20 MHz when AC+DC is selected(3-5%error).-当选择交流从 20 Hz 到
43、20 MHz(0.5-5%的误差)。(误差跟频率和振幅有关)/20 Hz to 20 MHz when AC is selected(0.5-5%error).(error depend on frequency and amplitude)7.功率表/Power meter 功率表用来测量开关电源的以下四个参量。率表温度测量表电子负载交流电源台式直流电源示波器是用来显示一个或多个随时间快速变化的电量的设备这个电量通常是指开关电源测试中的电压或电流大多数示波器是用阴极射线管显示的数字存储型示波器也有用液晶显示的示而变化数字存储示波器矢量显示对于非存储模式类似仿真示波器对于存储模式首先输入信号经
44、模数转换并存储在存储器中存储后的信号再经数模转换然后调整束的垂直位置这种类型的示波器现在已经逐步被淘汰数字存储示波器监控真示波器的功能重要的控制垂直垂直增益伏格垂直位置直流耦合交流耦合水平时间格水平位置触发为了使波形的起点在每个屏幕的位置相同使用触发是必要的否则不能显示稳定的波形源等电平沿偶合直流交流高频滤除触发延迟时间Power meter can be used to measure following 4 parameters to a switching power supply.-输入电压的有效值/RMS input voltage.-输入电流的有效值/RMS input curre
45、nt.-真实的输入功率/True input power.-输入功率因子/Input power factor 7.1 原理/Theory 功率表是通过将瞬间的输入电压和输入电流相乘然后取平均值来得到真实的 输入功率。Power meter measure true power by multiplying(analog multiplication)the instantaneous input voltage and input current,the product is then averaged out.通常有四个端口两个为输入电压两个为输出负载(至测试中的开关电源)Usually
46、there are 4 terminals:2 for input voltage,2 for output load(to switching power supply under test).输入电压和输出负载的高端在功率表内短接输入电压和输出负载的低端在功 率表内部通过一个电流测试电阻连接在一起。因此电压和电流都能测量。The Hi terminals of input voltage and output load are shorted inside power meter,the Lo terminals of input voltage and output load are c
47、onnected by a current measuring resistor inside power meter.Thus both the voltage and current can be measured.8.温度表/Thermometer 温度表用来测量温度。大多数的数字温度表都配用 K 型的热电偶。Thermometer is used for temperature measurement.In most case a digital thermometer plus K-type thermal couple is used.Equipment for switching
48、 power supply testing File:AC003.doc Page 8 of 11 Date:28-Dec-2001 8.1 原理/Theory 热电偶是由末端相连的两块不同材质的金属组成。如果两个连接点维持不同的温 度那么会产生一个 emf(电动势)温度差别越大产生的 emf 就相应越强。A thermocouple is made of 2 different metals joint at each end.If the 2 junctions are maintained at different temperatures an emf(electromotive fo
49、rce)is developed,the greater the temperature difference the higher the emf generated.实际应用中热电偶的一个末端扭在一起粘于被测设备上另一端分开连接 到数字温度计上。数字温度计本身保持在一个已知的温度上(有个内部的部件可 以测量这个已知的温度)。测量到的 emf 转换成温度差别。这样设备温度=温 度差别+数字温度计自身温度。In practice one end of the thermocouple is twisted together and attached to the body of a devic
50、e to be measured,the other end is separated and connected to a digital thermometer.The digital thermometer is maintained at a known temperature(there is an internal component to measure this known temperature),the emf measured is converted into a temperature difference.Then,device temperature=temper