[Elecraft] diode polarity

[Rick Shindley]

Someone was asking about the banded end of diodes and how to identify it.
Usually the cathode (banded end) is marked in an obvious manner. However, I
have a few small zener diodes that have colored bands allover them!

In case you just can't figure it out, don't despair! Just grab your favorite
Ohmmeter and measure the "resistance" of the diode in both directions.  In
one direction the resistance reading will be much lower.  In that case, the
BLACK Ohmmeter probe indicates the cathode (banded) end of the diode!  Note:
you may have to select a higher range to make this work, like R X 100 or
greater.  It depends on the design of the Ohmmeter.

Many modern multimeters have a diode test function.  The meter will indicate
the diode's forward conducting voltage drop on the display when the black
probe is connected to the cathode (banded) end of the diode (and, of course,
the red lead connected to the anode end of the diode). The forward voltage
drop indicates the type of diode under test, 0.4 V representing a Schottky
diode, for example. (0.2 V for germanium, 0.6V or 0.7V for "regular" silicon
diodes.)

Not to belabor the point, but zeners can be tested with an Ohmmeter as well,
but not for their zener breakdown voltage.  Zener diodes are silicon diodes
that have been made less "pure" so-to-speak, so they have a much lower, but
precise, reverse breakdown voltage characteristic. If they are "good", they
test like any other diode would.  That is, they conduct in the forward
direction like other diodes, so their banded (cathode) ends can be
identified by the black Ohmmeter probe when the meter indicates the lowest
resistance reading or a valid forward drop voltage (0.6V).

Rick KC0OV
K2 1360