How to Test a Zener Diode

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Hey guys, I am gonna describe the procedure how to test a zener diode. This article helps you to detect a zener diode whether it is good or defective. This test is much more effective to identify a zener diode that is soldered in your PCB is actually working good or not.
It can be done in two ways.....
  1. Using a Ohmmeter;
  2. Using a Voltmeter.
Let's see how to do that.

Zener diode Testing Using a Ohmmeter: 
Take your Multimeter. Set the knob to ohmmeter at higher range.Connect your multimeter positive lead to zener diode cathode and negative lead to the zener diode anode(See figure 1. Don't connect your body or finger with the diode or multimeter leads.Your body resistance will affect the test).However, you should get a large resistance value. For example, a few mega ohms.

Fig:1
Now, set the knob at a lower range. Connect your multimeter positive lead to zener diode anode and negative lead to zener diode cathode (See figure 2). At this point, you should get the value of resistance moderately low. For example, a few handred of ohms or a few kilo ohms. 

Fig:2
*If your observations are really like above, make sure that your zener diode is good.

*If you observe that the resistance you measured is very high for both (anode to cathode & cathode to anode) direction, make sure that your zener diode is opened. Because, a good zener diode never shows the very high resistance at forward biased direction (anode to cathode) compared to reversed biased direction(cathode to anode direction). You should replace your zener diode with a new one.


*If you observe that the resistance you measured is low for both (anode to cathode & cathode to anode) direction, make sure that your zener diode is shorted. Because, a good zener diode never shows the  low resistance at reversed biased direction(cathode to anode direction) compared  to forward biased direction (anode to cathode). You should replace your zener diode with a new one.

Zener diode Testing Using Voltmeter:
For this test, you should have (a) A DC voltage source such as battery, rated higher than your zener diode rated voltage or normally you can take a voltage supplier that will supply you a higher voltage than your zener diode rated voltage; (b) A resistor (1k ohms will be best); (c) A voltmeter or multimeter. 
Take your voltmeter or set your multimeter knob at voltage measurement point.Connect the resistor and zener diode in series(battery positive to one leads of resistor, another resistor lead to zener diode cathode and zener diode anode to battery negative).See figure 3. Zener diode should be connected in reverse biased direction with resistor. Measure the voltage across zener diode(multimeter positive to zener diode cathode and negative to zener diode anode). Multimeter should show the value of voltages almost the zener diode rated voltage. If  you observe like that, your zener diode is good.

Fig:3
*If you get a voltage that is below the rated voltage (may be zero) of zener diode, make sure that your zener diode is shorted. It should be replaced with a new one.

*If you get a voltage that is above the rated voltage of zener diode or almost the supply voltage. Make sure that your zener diode voltage is open. It should be replaced with a new one.

Now, start Testing your faulty circuit. Keep with this Blog. I will post how to test all other circuital elements.

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