Component Testing - Diode

Diode is a two terminal semiconductor device that allows current to flow in only one direction. Its terminal was called Anode and Cathode.

fig1. diode terminals Cathode and Anode

DIODE TESTING
Diode testing is very easy if you know some basic things about it such as biasing and meter polarity. As you can see in fig1, when a diode is connected in forward biased the flow of current will allow while on the other hand it oppose the flow of current. This only means that diode should be connected in forward biased so that the flow of current is possible. This biasing plays vital role in diode testing.

fig2. Forward and Reverse Biased

Multimeter polarity is another factor that we need to consider in testing diodes. Most of the analog multimeters have a leds that was reversed in polarity. The black led is positive (+) and the red led is negative (-). In this article we treat the red led as positive (+) and black led as negative (-) to show how diode biasing play its role in diode testing.

To test diodes please follow the steps below:

1. Set your multimeter in low resistance range.
2. Connect the positive probe to anode and negative probe to cathode. The diode will conduct and the meter will display a low resistance.
3. Reverse the connection. The meter needle should not deflects at all because the diode is not conducting.

fig3. Meter display a low resistance value because the diode is conducting

fig4. Meter needle is not deflecting because the diode is not conducting

Indication of Bad Diode

There are two possible indications of bad diode, shorted and open. A Shorted Diode when test using a multimeter will give a zero ohms resistance reading even the diode was connected in both forward and reverse biased.

fig5. Diode is connected in Forward biased but the meter display zero ohms resistance reading

fig6. Diode is connected in Reverse Biased and the meter still displaying zero ohms resistance reading

An Open Diode gives infinity resistance reading even the diode is connected in both Forward and Reverse Biased.

fig7. Diode is connected in Forward biased but the meter display infinity resistance reading

fig8. Normally, when diode is in reverse biased the meter will not deflect at all.