# Zener Diode Pointless Fun

Discussion in 'General Electronics Chat' started by beeson76, Mar 12, 2012.

1. ### beeson76 Thread Starter Senior Member

Apr 19, 2010
193
2
I am trying to understand Zener Diodes, so I decided to make a simple circuit, with several different diodes in place.

I never really understood the zener voltage and zener diodes: whenever someone tries to explain it, they always get in too deep for me, so this was why I decided to do a simple hands on experiment.

Does this experiment look to be correct: am I using the zener diode the way was was meant to be used. I kept with one resistor to keep things simple.

Any other help with understanding zener diodes, there use, and etc. would be greatly appreciated. Even some simple experiments would be beneficial too.

The reason for this experiment is just to see how a zener voltage affects in this case the brightness of the LED.

Thanks for the help and suggestions.

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2. ### Sparky49 Well-Known Member

Jul 16, 2011
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I would say, link them up to a multimeter and just take measurements of everything!

Consider using a variable resistor, see what changes and what doesn't.

Up until a month or two ago, I firmly believed that I could learn it all by reading books... Now I fiddling with everything, and taking measurements seeing what real effects things have.

You might find that after taking the measurements that everything that you've read/been told 'clicks' into place.

3. ### nigelwright7557 AAC Fanatic!

May 10, 2008
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A zener doesnt work until there is sufficient current through it to reach the working zener voltage.

4. ### Markd77 Senior Member

Sep 7, 2009
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There's something going wrong with your measurements or calculations.
If you calculate the current from the voltage across the resistor it is a wildly different value from the LED current you have noted.

5. ### jtrent New Member

Mar 11, 2012
26
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You can read my comments here where I have provided a pretty clear explanation of what is going on in your circuits. You did a good job. It just seems you are not understanding what is going on.

6. ### beeson76 Thread Starter Senior Member

Apr 19, 2010
193
2
I appreciate the replies. Yes I was noticing the different current values. I am reading books too, but I fell that reading is not the same as "experimenting" Im kinda glad I did this and I was going to go further with higher rated zeners, but the LED just won't light anymore with the next highest zener.

When you mention that zener voltages try to keep a constant voltage across it, what do you mean? For example the 1n4728 has a zener voltage of 3.3--so it will not allow voltage through until it reaches 3.3v right or has a voltage source above 3.3v. Or will it allow voltage up to 3.3v and nothing above 3.3v?

And current is what controls zener voltage right. Can someone explain that for me.

Thanks again for the help.

7. ### kubeek Expert

Sep 20, 2005
5,584
1,093
It will not allow CURRENT through it until the voltage across it reaches ~3.3V. Above that, the voltage will stay at 3.3V and current will increase.

Let say you have just a 9V battery, a 3.3V zener and 1K resistor all in series. Since you have enough voltage to open the zener, there will be 3.3V drop on it regardless of current. Then the current will be (9V-3.3V)/1K =5.7mA.

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8. ### kubeek Expert

Sep 20, 2005
5,584
1,093
Actually if you know how a forward drop of an LED works, then it is almost the same for a zener. The only difference is that zener shows the zener voltage when reverse-biased, whil LED shows forward drop when forward biased, and that zener when forward bisased has forward drop like a standard diode, ~0.65V

9. ### beeson76 Thread Starter Senior Member

Apr 19, 2010
193
2
Thanks Kubeek.

I like the simple explanation, thats what I wish I could get more of. Now I will go through each circuit and figure out all the measurements to see if everything looks good. I will post anything I find here.

Any other information that you guys seem like a new person who is learning about zener diodes in general would be interested in...that would be great too. Like sample circuits, simple reading material, examples...

Thanks again for the help. Appreciate it very much.

10. ### pilko Senior Member

Dec 8, 2008
213
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The most common zener configuration is a voltage regulator as shown in the schematic.
Try different value load resistors and also vary the input voltage and see what happens.
The chart will give you an idea what to expect. the red line is the input voltage and the green line is the voltage across the load.(and accros the zener).

pilko

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11. ### libra Member

Jul 27, 2012
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I am also read the zener diode in VOL.III-Semiconductors. I attach the circuit in that circuit, supposed the zener diode get damaged then can we get the voltage across R(load).

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12. ### kubeek Expert

Sep 20, 2005
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Second, is there any question you wanted to ask?

13. ### libra Member

Jul 27, 2012
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Yes i want to ask a question. i ask this question in this thread because it is related to my question, if not then i will start the new thread.

14. ### kubeek Expert

Sep 20, 2005
5,584
1,093
Then why don´t you ask it? You posted lots of declarative sentences, but not a single question.

15. ### Ron H AAC Fanatic!

Apr 14, 2005
7,012
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He asked a question. He just omitted the question mark.
The phrase in red is a question.
The answer is, if the zener is open-circuit, then what remains is a simple voltage divider. The voltage will be 45V*500/(500+1k)=15V.

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16. ### ScottWang Moderator

Aug 23, 2012
6,763
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The attachment is edited to explain for someone that how a Zener diode work when using diode, it's more easy to understand, I hope it can help you some more.

The Equivalent Circuit of Zener diode Using Diode and LED Protection

• ###### ZenerAndDiodeEquivalentCircuitProtectionLED.gif
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17. ### ramancini8 Active Member

Jul 18, 2012
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Get a copy of the Motorola Zener Diode Manual and read chapters 1,4,6, and 7 to obtain a useful knowledge base. Playing in the lab is fun, butit is not a well rounded education.

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18. ### Evil Lurker Member

Aug 25, 2011
116
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Hook an LM317 configured as a constant current source using a low value trim pot, adjust your current to the specs on the datasheet, and you can then see just how far off your zener is by measuring the voltage drop across the diode under test. Generally a "safe" value from what I have seen is around 10ma, with lower voltage ranked zeners depending on their wattage being tested at currents up to 50ma or more. It should be noted that a zener's "heel" varies with the amount of current applied and can vary quite a bit.

19. ### libra Member

Jul 27, 2012
62
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Thank you ScottWang. I will do this in LAB for more clarity.

20. ### MKCheruvu Member

Nov 20, 2012
30
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We have to ensure/check for the following conditions:
1) Vbattery > (V led+ Vz)
2) R series <= [Vbattery - {V led+ Vz}]/Izk - {Izk Knee Current from Zener data Sheet-(say 1mA)}
3) Izener(operating/test) > Izk - ( Zener Test CurrentFrom Device data Sheet).
4) Ensure Max -I led/ Iz(which ever is less) - as Series current rating is not crossed.