Zener diode failure modes-difference between Open diode and short or shorted diode

This page describes zener diode failure modes viz. open and short. It compares open diode vs shorted diode and mentions difference between open diode and shorted or short diode failure conditions.

Introduction: • As we know zener diode is specially designed highly doped p-n junction diode.
• Unlike normal diode, it is designed to operate in reverse biased region.
• Zener diode appearance and symbol are shown in the figure-1.

• Zener diode characteristic is shown in the figure-2 below. Zener diodes are designated based on its zener voltages and are available in various ranges 3.9, 5.1, 6.2, 9.1 etc.

Some of the parameters which are tested during zener diode measurements include zener voltage (Vz), current @ Vz, zener resistance (Rz) etc.

Zener diode test | Open diode test

There are two ways open condition of the zener diode can be checked or verified viz. resistance test and voltage test.
➤Resistance Test: In this test, set the multimeter in resistance test mode. Now connect the Positive or red cable of multimeter to anode and negative or black cable to cathode of the diode. In this test, multimeter should read low resistance (about 450 KOhm). When the diode is open, it reads high resistance in both the directions. Normal healthy diode should never read high resistance in forward biased condition.
➤Voltage Test: In this test, set the multimeter in voltage test mode. Now connect red cable with anode and black cable with cathode of the zener diode. In this test, multimeter should read voltage approx. near to zener voltage (Vz, say 5.1 V) of the diode. This condition is healthy condition of the diode. When the diode is open, multimeter reads high voltage or near to supply voltage (say 9 V).

Zener diode test | short diode test

There are two ways short condition of the zener diode can be checked or verified viz. resistance test and voltage test.
➤Resistance Test: In this test, set the multimeter in resistance test mode. Now connect the Positive or red cable of multimeter to cathode and negative or black cable to anode of the diode. In this test, multimeter should read high resistance (about 2.2 MOhm). When the diode is shorted, it reads low resistance in both the directions. Normal healthy diode should never read such low resistance in reverse biased condition.
➤Voltage Test: In this test, set the multimeter in voltage test mode. Now connect red cable with anode and black cable with cathode of the zener diode. In this test, multimeter should read voltage approx. near to zener voltage (Vz, say 5.1 V) of the diode. This condition is healthy condition of the diode. When the diode is shorted, multimeter reads much low voltage (about 0V) compare to rated voltage. This is defective condition of the diode.

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