zener diode Testing | zener diode Test and Measurement

This article on zener diode testing covers various test and measurement parameters used to evaluate zener diode. It mentions test setup used for various measurements during zener diode testing.

What is zener diode?

Introduction: • Zener diode is specially designed highly doped p-n junction diode.
• It operates in reverse biased condition. Current flows from anode to cathode once zener voltage is reached. The zener diode operates in breakdown region unlike normal diode.
• The figure-1 depicts zener diode appearance and symbol.

• It is made to be used in breakdown region as long as series resistor limits the current.
• The figure-2 depicts zener diode characteristic. As shown, As V_R increases, reverse current is negligible until V_R reaches breakdown voltage V_Z. Beyond this, I_R increases suddenly. V_Z is known as zener voltage or reference voltage. If V_R decreases below V_Z, I_R becomes negligible once again.
• zener diodes are available in various ranges e.g. 3 V, 3.9V, 5.1V, 6.2V, 9.1V, 10V, 15V etc.

zener diode Measurements

Typical test parameters of the zener diode are as follows.
• Zener voltage (Vz)
• Current at Vz
• Power rating
• Zener resistance (Rz)
• Voltage tolerance
• Temperature stability
• Junction Temperature
• Package type

zener diode testing youtube video

Test Setup for zener diode Testing

Following diagram shows test setup used during zener diode testing. Following are the common failures observed in zener diode. Zener diode tests are useful to determine whether zener diode is good or defective.
• Open diode
• Shorted diode (anode to cathode)
• Conduct current at voltage level below ratings

Zener diode resistance test using multimeter

During these tests, multimeter is placed in simple resistance mode or diode test mode.
➤Positive probe cable is connected to anode of zener diode where as negative probe cable is connected to cathode of diode. In this setup, multimeter should read low resistance (About 450 KOhm).
➤When the above probes are reversed, diode is reverse biased. In this test multimeter should read high resistance (about 1 MOhm).

• When diode is open, it reads high resistance in both the directions.
• When diode is short, it reads low resistance in both the directions.

Zener diode voltage test using multimeter

During these tests, multimeter is placed in voltmeter mode.
➤In this test, zener diode is connected in reverse biased mode as shown with series resistor. If zener diode measures voltage near to rated zener voltage (Say 5.1 V) it is considered to be in good condition.
• When diode is open, it reads very high voltage or voltage having value near to supply voltage. This diode should be replaced.
• When diode is short, it reads much low voltage than rated voltage (near 0v). This diode is defective and should be replaced.

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