Zener Diode Checker




Introduction: Zener Diode Checker

About: Why would i buy something ready made when i can make it myself with half the features for twice the money? DIY!

If you are like me and your and your parts storage is less than perfect, you may have more than one Zener diode in the same compartment.

A Zener diode is like a one way check valve,with a twist. Unlike a regular diode that is just a on way check valve the Zener is also a voltage regulator. What ever the preset voltage is, that is the regulated voltage that will be allowed to pass through. If hooked up in the other direction then the check valve part of the diode comes into play, no voltage gets through.
I realize this is a simplified explanation and more factors come into play. But for the most part this is what they do.

Thats why if there is more than one Zener stored in the same place and they are not marked as to what voltage they are. It is impossible to know.

So, if this the case for you then you need a Zener diode checker.

To operate this checker is very simple. You put the Zener on the checking lugs that have the magnets. Hook up the power on the back lugs. Turn on the power to the back lugs. Turn sw on on the checker. Adjust pot to get the highest voltage on the meter. That is your Zener voltage.

I do not have pic's from the start of this build. It was started before i joined Instructables. So these build pics are just the last part.  

Step 1: The Schematic

The schematic i ended up using wasn't the first one i tried and i didnt pick it because it was the simplest. It is the one that worked the best for me in the end.
I think the first checker was affected by the charging and discharging of the cap. Made it difficult to get a steady readout. I am not really sure but it was hard for me to use.  

The hand drawn schematics are just from my reference book that i use. They are the same as the previous 2 schematics. 

Step 2: Assembly

There is some extra wires left here from the first build that have not been removed yet.

I soldered the 22K resistor from the wiper on the pot to the pos line as per the diagram. One end of the pot i will call the neg post goes to the neg line. It was easiest to attach at the volt meter, as was the pos but on the pos line. Neg from the meter went to the gnd post on the outside power connection.  The other end of the pot i will call the pos lug goes to the pos post also on the outside power connection.
You can see all the extra wires have been removed and the wiring has been cleaned up.
For the 12v dc power lugs, I started by soldering the leed on the lug then bend it around just under the head and finish by soldering it complete. All the way around.

I choose a location that was as out of the way as possible yet convenient to attach the 12vdc power. I choose the back of the box. Marked the holes, drilled 1/8 holes. Attached the lugs with the soldered wires attached from inside out and secured with a nut. I used a black felt pen and colored the neg black and left the pos natural color.      

The power source comes from my power supply 12v dc. Just hook it up with alligator clips.

Step 3: Testing

Previously i had installed several components.The test lugs, I added small magnets at the top to attach the Zener to for ease of checking. The 100k pot, switch and the volt meter. 

If you attach the Zener backwards it will read just above 0.

This is 6.2v Zener i am testing. You see it shows around 6v. An analog gauge may not be as accurate a digital read out.. An analog readout has some room for interpretation due to viewed angle ect, but it can get you close.
I have noticed on lower voltage Zeners such as 2.8 volts the reading is lower that the rated voltage. Even with that incorrect lower voltage it is still better that not knowing what the voltage it is. 

If anybody decides to make this or some version of it i would love to see what you came up with.

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    4 Discussions


    8 years ago on Introduction

    Good, useful stuff, but about your low / inconsistent readings, it may be due to the following:

    1. Analog meters have a fairly low impedence, usually in the 10-100k range. What this means is that a large percentage of the current is going through the meter and not the Zener. Digital meters have impedences around 1Meg and so will not load the circuit much.

    2. Zeners require upwards of 5mA going through them to work reliably. Most are rated at 0.5 or 1-watt so this is only a fraction of their peaks.

    Maybe by changing the resistors 10x smaller (10k and 2.2k), things will be more stable.


    Reply 8 years ago on Introduction


    Thanks for your comment. I will look into it.



    8 years ago on Introduction

    Good one. I had not heard that b4.


    8 years ago on Introduction

    True story. Broken down on the side of the highway, Joe W. futzed with the old BSA. As he was doing a little rewiring, a state trooper pulls up and asks Joe what the problem is, to which Joe replies, "The Zener Diode is shot." The trooper gives Joe the dagger eyes and says "Just fix the thing and get a move on. I'm not stupid. Zener Diode my ...".