Author Archives: Teefactor

I am an electrical and electronics enthusiast; with decades of experience in the field. I love teaching what I know and hope to be of help to as many as I come across.

Testing Diodes With A Digital Multi Meter

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In this post I will describe in simple terms a concise process required to test a P-N junction diode. I hope you find this helpful.

Diodes are small electronic devices that allow electric current to flow through in only one direction. It works by having low resistance in one direction and high resistance on the other. You’ll have to occasionally test a diode—which is typically made from a semiconductor material to make sure it’s working properly. You can check the health of a standard diode with either a digital or analog multimeter, which will measure in ohms (Ω) or volts. This post will describe how you can test it using a digital multimeter. There are different types of diodes—-Zener Diodes, light emitting diodes(L.E.D’s), P-N junction diodes, etc. We’ll however talk only about P-N junction diodes in this post.

The first shows the circuit symbol of P-N junction diodes. The other two below shows the 3 dimension representation.
This shows a P-N junction diode sitting on a prototype board. The left side is the anode and the right is the cathode—which has the silver line.

Take these simple steps to test a P-N junction diode:

Shut off the power source if the diode is in a circuit.

Switch the meter to diode test. You should see a diode symbol on the screen for most multimeters. Connect the positive probe(Red probe) to the anode and the negative probe(black probe) to the cathode. You should get a reading ( Somewhere around the number you see on my multimeter). Note also that this gives you an idea of the voltage drop that the diode would produce when connected correctly in a circuit.
Now reverse the probes. If you notice, this time the positive probe is connected to the cathode and the negative to the anode. This time you shouldn’t get any reading.
If in any of the position, you get this reading, it means that the diode is shorted and is bad, also if you don’t get any reading at all in both positions, the diode is open circuited and is bad.

I hope this helps. Feel free to ask your questions in the comments section. Thanks.