Thursday, February 7, 2013

How to test a diode


Diodes can be tested using a multi meter. It is normally the resistance of the diode in both forward and reverse directions that is tested. There are however a number of points to remember when testing diodes.
The diagram below (Figure 1) shows how to connect a digital meter to test the diode. There are a number of things to remember:

  • Make sure you are using the diode range.
  • Using a digital meter, connect the black lead to the cathode and red to the anode (forward bias - around 1kΩ).
  • Reverse the meter connections (reverse bias - infinity reading).
MUST BE REMEMBER!

If you are using an analogue meter the above polarities are reversed.

SOME METERS give a reading of the junction potential (in volts) CHECK YOUR METER INSTRUCTIONS.


Figure 1. How to test a diode


Bad Diode:
In the case of a bad diode, you will have one of two situations. First, if the meter
indicates ZERO (as it will if the probes are touched together) both ways, the diode has
shorted. Or, second, the meter indicates INFINITY (as it will if the meter probes are not
touched together) both ways, meaning the diode is open.



Reference:

[1] http://www.learnabout-electronics.org/diodes_05.php 
[2] http://www.lesterelectrical.com/techservice/servicedocs/diodetesting.PDF