The polarity test is designed to determine the orientation of thediode safely and quickly prior to performing functional testson the device.
The breakdown characteristics of the diode areused to generate an indication of the diode’s polarity.
By properly choosing a test current level and voltage compliance limit, it’s possible to distinguish a correctly oriented forward-biaseddiode from an incorrectly oriented reverse-biased diode.
If apositive current is sourced through a properly oriented diode,the diode will be forward-biased and the resulting forward voltage will generally be small (typically less than 1V).
If the sametest current is forced through a diode with reversedorientation,then the diode will be reverse-biased and the resulting reversevoltage will be much higher than the forward voltage and willeasily exceed the compliance limit.
Thus, by simply checking the compliance state of the instrument, it’s possible to determine if the diode is in the forward or reverse orientation.
If compliance is reached, the diode is in reversed orientation; otherwise, it’s in forward orientation. It would be possible to perform this test by actually measuring the voltage drop across the diode and comparing it to forward- and reverse-biased limits, but simply checking for compliance is generally faster.
