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Many tests require sourcing a known current and measuring a voltage; others require sourcing a voltage and measuring the resulting current. Therefore, high speed test instrumentation with integrated, synchronized sourcing and measuring capabilities is ideal for these types of tests.

很多测试需要提供已知的电流然后测量电压，而另外一些测试需要提供电压然后测量产生的电流。因此，具有集成的、同步的源和测量功能的高速测试仪器[1]对于这类测试是非常理想的。

Forward Voltage Test
In an LED test sequence, the forward voltage (V_F) test verifies the forward operating voltage of the visible LED. When a forward current is applied to the diode, it begins to conduct. During the initial low current source values, the voltage drop across the diode increases rapidly, but the slope begins to level off as drive currents increase. The diode normally operates in this region of relatively constant voltage. It is also quite useful to test the diode under these operating conditions. The V_F test is performed by sourcing a known current and measuring the resulting voltage drop across the diode. Typical test currents range from tens of milliamps to amps, while the resulting voltage measurement is typically in the range of a few volts. Some manufacturers use the results of this test for binning purposes because the forward voltage is related to the chromaticity (the quality of color characterized by its dominant or complementary wavelength and purity taken together) of the LED. 

正向电压测试

在LED 测试[2]序列中，正向电压[3]（V_F）测试检验的是可见光LED上的正向工作电压。当在二极管上加载一个正向电流时，它就开始导通。刚开始在低电流下，二极管上的电压降快速上升，但是随着驱动电流的增加，电压斜率开始变平。二极管一般工作在这个电压相对恒定的区域。在这些工作条件下对二极管进行测试也非常有用。V_F测试需要提供一个已知的电流然后测量二极管上产生的电压降。典型的测试电流范围从几十毫安到几安，而产生的电压大小通常在几伏的范围。有些制造商利用这种测试的结果进行器件分拣，因为正向电压与LED的色品（由色彩的主要或者补色波长及其纯度共同表征的色彩品质）相关。

[1]高速测试仪器：http://www.keithley.com.cn/products/dcac/currentvoltage/highcurrent/?mn=2651A

[2] LED测试 实验室：http://www.keithley.com.cn/re/cel

[3] 正向电压测试应用：http://www.keithley.com.cn/products/localizedproducts/currentvoltage/2400