一般开关电源供应器的测试仪器及其特性精.docx

1、一般开关电源供应器的测试仪器及其特性精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 probe.- 数字式电压表 /DVM.- 有效值表 /RMS meter.- 功率表 /Power meter.- 温度测量表 /Te

2、mperature 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 of one or more rapidly varying electrical quantities

3、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 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

4、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(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

5、/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 in memory, then the content of the memory

6、 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。Digital storage scope, monitor display (Tektronix TDS3012): The display i

7、s 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.2.2 重要的控制 /Important control2.2.1垂直 /Vertical.- 垂直增益(伏/格) /Vertical gain (V/div).- 垂直位置 /Vertical position- 直流耦合 /DC coupli

8、ng- 交流耦合 /AC coupling2.2.2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 the waveform on every screen is the same, otherwise no stable waveform can be seen on the display.- 源CH1, CH2, Lin

9、e 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 th

10、e 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-CH2。To measure the voltage waveform across 2 swinging node (e.g. forward converter rectifi

11、er), 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。然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 circuit other than ground provided the circuit under test is floating. However, 2 probe ground must not be connected to 2 differe

12、nt 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,

13、 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 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 scre

14、en. 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. TDS3012/3014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 scre

15、en. 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 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 p

16、robe3.1 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 impedance 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

17、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 capacitance 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

18、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。 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 pF. Input 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

19、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 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

20、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 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 b

21、eing 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 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

22、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 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

23、 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 P602110mA/mV文件3dB的截止频率点为120Hz2mA/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/mV, 450Hz at 2mA/mV). 对于P6021电流波形峰值不能超过15Amp。Current waveform shall no

24、t exceed 15 Amp peak for P6021.5. 数字式电压表 /DVM5.1 直流电压测量 /DC voltage measurement 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 required, 3 1/2 digit, 4 1/2 digit, 5 1/2 digit di

25、splay 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.5.2 直流电流测

26、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 voltage measurement, an rms converter ci

27、rcuit 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. The other is average responding but cali

28、brated 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 is accurate from 50 Hz to 10 KHz only f

29、or 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 lead is included. For high resistanc

30、e 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, 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 als

31、o 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 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

32、earth. However, there is high capacitance between black terminal and earth. So the black terminal shall not be connected to nodes with high 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