开关电源供应器的测试仪器及其特性

1、Equipment for switching power supply testingFile: AC003.docPage 1 of 11Date: 28-Dec-2001弓 |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.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

3、 of 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.示波器类型 /Type of

4、 oscilloscope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，

5、矢量显示(Tektronix 2232):对于非存储模式，类似模拟示波 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 wit

6、h A/D and stored 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(类似电脑 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 似模拟示波器的功能。Equipment fo

7、r switching power supply testingFile: AC003.docPage 2 of 11Date: 28-Dec-2001Digital 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 fu

8、nction as an analog scope.重要的控制 /Important control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水平 /Horizontal-时间 /格 /Time/div.-水平位置 /Horizontal position.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 po

9、int of the 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，TVO /Coupling : DC, AC, HF Rej, TV触发延迟时间。/Trigger hold time.使用注意事项 /Precaution in use.接地问题 /Earthing prob

10、lem.通常，示波器的地是与安全地相连，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

11、转换整流器)，必须用相减的方法， 例如 CH1-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他直流电平处。然Page 3 of 11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 ground may be connected to other DC level in the ci

12、rcuit 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.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，其他纹波成份会被掩盖。Digital osc

13、illoscope 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 amplitude spikes. In peak-detect mode, it will

14、 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 different on consecutive waveform.TDS3012/30

15、14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 varying between waveforms, then t

16、he spike width must be very narrow, the horizontal time/div shall be set faster to obtain consistent spike amplitude.电压探头 /Voltage probe电压探头的类型 /Type of voltage probeX1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 impedance follow that of scope input imp

17、edance (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 of 1 Mohm input impedance, input c

18、apacitance around 13pF. 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。Page 4 of 11X100 probe : e.g. Tektronix P6009, attenuation of 100:1, input impedance 10Mohm when used with a scope of 1

19、Mohm input impedance, input capacitacne 2.5 pF. Input voltage limited to 1500V for DC and low frequency.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 a scope/probe combination for X10 and X100 probe changes. Recalibrate the high frequency response of the probe with

20、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 ground 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

21、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 lower 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 p

22、robe to hot parts, e.g TO-220 metal plate, or components lead that are being soldered.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。AC current probe act as a current transformer which the core can be opened and clamped on a current carr

23、ying conductor. A voltage will be developed at the termination at certain ratio. Only AC current above certain frequency can be measured accurately.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。(例如Tektronix P6021，10mA/mV档 3dB的截止频率点为120Hz，2mA/mV档为450Hz)。AC current probe shall not be used to measure lo

24、w freqeuncy current wavform. (e.g. Tektronix P6021, 3dB point is 120Hz at 10mA/mV 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.数字式电压表/DVM直流电压测量 /DC voltage measurementPage 5 of 11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 fu

25、nction is to convert a DC voltage into a digital display which can be read easily. Depending on accuracy required, 3 1/2 digit, 4 1/2 digit, 5 1/2 digit display or more is available.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

26、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 measuring high impedance circuit.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

27、convert the current to a DC voltage signal.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 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

28、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. The 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 switchi

29、ng 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 is accurate from 50 Hz to 10 KHz only for general purpose DVM.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 measuremen

30、t, the DVM will pump out a small current and measure the voltage across the 2 terminals, so the resistance of the 2 lead is included. For high resistance measurement, the lead resistance is negligible.数字式电压表在测量低于20欧姆的电阻时，会因为引脚的电阻而使测量不准 确。除非它是一个四线欧姆表。DVM is not accurate in measuring resistance below

31、20 ohm due to the lead resistance,Page 6 of 11unless 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 calcul

32、ate the resistance.使用注意事项 /Precaution 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 not be connected to nodes with hi

33、gh voltage swing.最大电压限额的处理，例如GDM8135。Take 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 th

34、e black terminal to any voltage higher than 500Vrms with respect to safety earth.)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.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 convert

35、er, frequency response can be very high, up 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.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。

36、For Fluke 8921A, both the red and black terminal are floating with respect to earth.However, there is high capacitance between black terminal and earth. So the blackEquipment for switching power supply testingFile: AC003.docPage 7 of 11Date: 28-Dec-2001terminal shall not be connected to nodes with h

37、igh voltage swing.最大电压限额的处理，例如Fluke 8921A。Take care 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 M

38、Hz when AC+DC is selected (3-5% error).-当选择交流，从20 Hz到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)功率表 /Power meter功率表用来测量开关电源的以下四个参量。Power meter can be used to measure following 4 parameters to a switching power supply.输

39、入电压的有效值/RMS input voltage.输入电流的有效值/RMS input current.真实的输入功率/True input power.输入功率因数/Input power factor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 averag

40、ed out.通常有四个端口：两个为输入电压，两个为输出负载(全测试中的开关电源)Usually 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, t

41、he Lo terminals of input voltage and output load are connected by a current measuring resistor inside power meter. Thus both the voltage and current can be measured.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

42、-type thermal couple is used.Page 8 of 11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，那幺会产生一个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 force) is developed, the great

43、er 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 device to be measured, the ot

44、her 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 = temperature difference

45、 + digital thermometer temperature.使用注意事项 /Precaution in use热电偶的测试末端应对风屏蔽。The measurement end of thermal couple shall be shield from wind.如果测量设备很小，热电偶的热传导效应显着，则测量的温度会较低。If the measure device is small, the heat conduction effect of thermal couple significant, measured temperature will be lower.热电偶必须连

46、续的连接在测量设备与温度计中。如果中间有其他节点，则该节点 的温度必须与数字温度计本身的温度相同。Thermal couple must be continuous from the measured device to the digital thermometer. If other junctions are inserted in between, those junctions must be at same temperature as the digital thermometer.电子负载 /Electronic load电子负载是用来作为一个可调负载。/Electronic

47、load is used as an adjustable load.操作模式 /Mode of operation电子负载可以设置为恒流，恒阻和恒压模式。Electronic load can be set for constant current, constant resistance and constant voltage operation. 恒流模式(CC) : /Constant current mode (CC):通常能够调节两个电流。从一个电流转换到另一个电流只需简单的一个按钮，或 者在一个可以调节的频率下自动切换。这种模式很方便用来开关电源的动态负载 测试。当开关电源处于

48、恒流模式，则不可以使用电子负载的恒流模式。否则，电 子负载只能是完全导通或完全截止，直到开关电源改变到恒压模式。Page 9 of 11Usually 2 currents can be preset. Changing from one preset current to another can be simple as pressing a button, or switch automatically at an adjustable frequency. This made it very convenient for testing performance of switching

49、power supply at step load. CC mode cannot be used when power supply under test is operating in CC mode. Otherwise electronic load will be either fully on or fully off until power supply change to constant voltage mode. 恒压模式(CV) : /Constant voltage mode (CV):在这种模式中，电子负载相当一个可变的稳压管。当开关电源处于恒压模式，则 不可以使用电

50、子负载的恒压模式。否则，电子负载只能是完全导通或完全截止， 直到开关电源改变到恒流模式。Prodigit的电子负载没有恒压模式。In this mode the electronic load behave as a variable zener. CV mode cannot be used when power supply under test is operating in CV mode. Otherwise electronic load will be either fully on or fully off until power supply change to consta

51、nt current operation. Prodigit electronic load do not have constant voltage mode. 恒阻模式(CR) : /Constant resistance mode (CR).在这种模式中，电子负载相当一个可变电阻。恒阻模式的设置可以是用来测试工 作于恒压模式或恒流模式的开关电源，柏怡自制的电子负载无恒阻模式。In this mode the electronic load behave as a variable reistor. Constant resistance setting may be used to te

52、st power supply that work in either CV and CI mode. PI built electronic load do not have CR mode.输入电压的范围/Input voltage range.Kikusui的电子负载，最大输入电压是在直流60伏。对于最小输入电压，当输入 电压大于1.8伏时，它会在一定延迟后导通；如果输入电压低于1.4伏便截止。For Kikusui electronic load, the maximum input voltage is 60Vdc. For minimum input voltage, it wil

53、l start to conduct after some delay when Vin is above 1.8 V and stop conduct when Vin is below 1.4V.Prodigit的电子负载，最大输入电压是在直流60伏。对于最小输入电压，当输 入电压大于1.2伏时，它会导通；如果输入电压低于0.4伏便截止。For Prodigit electronic load, the maximum input voltage is 60Vdc. For minimum input voltage, it will start to conduct when Vin i

54、s above 1.2V and stop conduct when Vin is below 0.4V.使用注意事项 /Precaution in use9.3.1电子负载不适用于测试开关电源的起机特性。Electronic load is not suitable to test the start up capability of switching power supply.对于Kikusui的电子负载，从输入电压加入到拉预设值电流，期间有10毫秒的 延迟。在这10毫秒期间并不拉电流。这种负载对开关电源来说要比电阻负载容 易启动。For Kikusui electronic load,

55、 there is a 10 msec delay from applying input voltage to drawing presetted current. During that 10 msec no current is drawn. This load is easier for power supply to start up than resistor load.Page 10 of 11移除输入电压后，如果在90毫秒内输入电压重新加入，电子负载会拉一个比预 设值大很多的电流。(例如，预设值为0.2A,但是电子负载会在1毫秒内拉3A的 电流。)After removal o

56、f input voltage, the electronic load is ready to sink a much larger current than the preset one if voltage is re-applied within 90 msec. (e.g. preset 0.2 A, but the electronic load can draw 3A for about 1 msec and than resume 0.2A when voltage is re-applied within 90 msec).如果电压移除大于90毫秒，电子负载会照例在输入电压后10毫秒才拉电流。If the voltage is removed for more than 90 msec, the electronic will start to sink current 10 msec after the application of voltage as usual.对于Prodigit电子负载，在输入电压到有拉电流期间并无延迟。这种负载对开关 电源来说，比电子负载更难启动。For Prodigit electronic load, there is no delay from applying input voltage to drawing prese