Zener Tester




Introduction: Zener Tester

About: My channel is interested in electronics and doing projects at home with recycled gadgets


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?

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

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:

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


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3 years ago

Note that in the instructable schematic based on a LiIon cell, the
typical 3-wire voltmeter display should be capable of being powered
directly from the LiIon - you can delete the 12V linreg, and the two filter caps, running the OUT from the boost to the resistor, and the ground to the zener. Red lead for the voltmeter should connect at the IN+ to the boost (so after the on/off switch). The regulator and capacitors appear to be leftover components from the higher voltage transformer design, but are unnecessary when you have a convenient 3-4V battery supply. Those voltmeter displays have an onboard LDO.

I am unclear on the purpose of the LM317 in this circuit - out of curiosity, I even watched the video, but outside of the names of some components, it appears to be entirely in an Arabic language, so I couldn't parse an explanation. Thing is, the 4.7K resistor should do a fine job of limiting current. With a 30V supply for instance, Ohms law dictates I = V/R, so 30/4700 = 0.006382A (6.4mA).

The 50V cap used in the schematic would be fine for the 30V transformer supply version, but 1000uF is entirely too much capacitance for this purpose.

For charging a capacitor bank from a low voltage source through a boost circuit, I use a zener in series with an LED as both a regulator and as an indicator that the zener voltage has actually been reached. With a lower capacitance capacitor of sufficient voltage instead of the large bank, the same circuit can be used to characterize a zener by measuring the voltage across the zener itself (or being sure to account for the Vf of the LED, which leads to an output voltage (at the capacitor) about 3.0-3.4 V higher than the zener voltage, depending on LED type).

Without an indicator like this, you might measure a voltage that is close to your max supply voltage, which could still be lower than your unknown Zener voltage - which doesn't mean that the Zener voltage has actually been reached. If the LED illuminates, it will do so only because the Zener is conducting - if it isn't illuminated, then the Zener is not conducting, and either the Zener is failed open, the Zener rating is higher than your voltage, OR, you're dealing with a non-zener diode with a high reverse breakdown voltage.

Attached image shows a compact 16x21mm PCB I made for cap bank charging - the indicator LED gets press fit into a snug hole in the faceplate of the cap bank (so no need for mounting screws) and the board incorporates the boost circuit capable of producing voltages of about 60V for testing. The zener needn't be soldered in place - that could have wires with clips or whatever soldered for clipping to a component needing measurement, or a PCB with pads to seat a MELF SMD resistor on.


3 years ago

What size in Watts is the 4.7k ohm resistor?


Question 3 years ago on Introduction

I built this nice construction and it works like a charm. Thanks for sharing.
I just want to know the role of LM317 in the circuit, when the output pin is shorted to Adjust pin.


5 years ago

nice and cnstructive project thanking you for shearing


5 years ago

Works like a charm! Thanks for sharing.


5 years ago

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