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Zener Diode Checker

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Picture of Zener Diode Checker
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.  
 
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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. 
qs2 years ago
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.

WWC (author)  qs2 years ago
qs

Thanks for your comment. I will look into it.

WWC
WWC (author) 2 years ago
Good one. I had not heard that b4.
dreamberry2 years ago
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 ...".
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