Introduction: Zener Tester

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We will create an electronic device to test the zener diode voltage.

First , Theoretically we will learn how the Zener diode work?

Let's get started

Step 1: How the Zener Diode Work?

Picture of How the Zener Diode Work?

The first thing to know is that the circuit symbol for zener diodes looks very similar to other diode symbols.

Make sure you don't get them confused because they behave very differently, and they are used for very different things! So what's special about zener diodes?

Regular diode VS Zener diode:

Step by step we will learn how it works and how Zener diode current passes in two directions?

Zener diodes work exactly like a standard diode, with the exception of one thing.

When the zener is on in the forward direction, we say it is "forward biased".

The diode won't even turn on and allow current to flow unless you have at least 0.7 volt with silicon diode and 0.3 volt with germanium diode.

But going the other way, In reverse biase.

Since current is flowing backwards, we say the Zener diode is "reverse biased". This property of having a predictable voltage drop is what makes Zener diodes useful.

Step 2: Three Ways to Measure Zener Diode Voltage

Picture of Three Ways to Measure  Zener Diode Voltage

This simple circuit show you how to measure the Zener diode.

•The easiest way to measure the Zener voltage as shown by connecting 1K Ohm in series with the Zener diode.

•The battery or power supply must be larger than the voltage rating of the diode.

I have used 30 volts as a power supply to the circuit.

The second circuit i used a 30V transformer as a power supply.

the third circuit i used ( 3.7 Li-Ion battery + charger + DC-DC boost converter) as a power supply

Step 3: Step by Step How to Make a Device Measuring Zener Diode Voltage:

Picture of Step by Step How to Make a Device Measuring  Zener Diode Voltage:

With photos and videos you can understand the steps of how to make a device measuring Zener diode voltage



kamil47 (author)2017-03-07

Very nice project.

7812, 12V regulator is used to power voltmeter, but LM317 function is not clear. What is LM317 for?

Voltage for Zener diode is slightly dependant on diode current. I suggest to measure voltage drop on resistor 4k7 and calculate current or measure current directly. Or the best solution is to alternatively switch two resistors in series with Zener diode and measure Zener voltage for two current. (Small current Zener diodes and more powerful Zener diodes.

medhatko made it! (author)kamil472017-03-07


According to LM317 data sheet

LM317 by connecting (adj+out) legs to limit the current throw the Zener diode


kamil47 (author)medhatko2017-03-07

Hallo, thanks for explanation. You are right, there is current limitation done by LM317 for about 1.5A. But LM317 is in this case useless. There is resistor

4700ohms in series with Zener diode and protecting this diode. Assuming that input voltage is about 47 V and and points for Zener diode are shorted, there is maximum current 10 mA.

indika154 (author)2017-03-07

nice and cnstructive project thanking you for shearing

MichaelB1098 (author)2017-03-05

Works like a charm! Thanks for sharing.

3366carlos (author)2017-03-05

very good.

BeachsideHank (author)2017-03-04

This can be a very useful device, thanks for sharing your concept. ☺

About This Instructable




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