I do not have a magnifier glass handy. And many a times I saw Diode Numbers get wiped out after reusing the diodes. Is there an easy way to distinguish between DO-35 packaged Switching diodes like the very popular 1N4148 and 0.5Watt Zener diodes using multimeter?

Even a simple circuit would also work for me. It would be awesome to keep the circuit handy as a tester and use it everytime I need.

  • \$\begingroup\$ 9 V battery comes to mind to reverse bias the zener. \$\endgroup\$ – winny Aug 11 '16 at 20:48
  • \$\begingroup\$ @SpehroPefhany Of course you are right, complete brain fade :) Removing my comment. \$\endgroup\$ – John D Aug 11 '16 at 21:34

How about two or three 9V batteries in series with a 10K resistor. Connect the diode in a series circuit both ways, and measure the voltage across the diode each way.

The diode and zener will both measure about 0.6V in the forward direction, and the diode will show the battery voltage when reversed, while the zener will show the zener voltage, if less than the battery voltage, otherwise it will look like the diode.

If the zener happens to be (say) a 200V zener you would need 200V to test it, which would be dangerous.

  • \$\begingroup\$ '200V' would not be my case! I work with 24V zener max :) Thanks Spehro. the solution looks great to me! \$\endgroup\$ – sribasu Aug 13 '16 at 6:24

You could try something like this. If you want to make it more robust, use the voltage across the diode into a transistor amplifier (driving the LED).

LED (red thing on the right side of circuit) is on if it's a zener, off if it's a diode.

simple zener tester


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