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Topic: Zener Diode not Zenering at all ;-( ... (Read 2625 times) previous topic - next topic

Docedison

Just a question but how do you know that the signal you see when you turn on the lamp isn't due to a ground 'artifact' or false indication. Frequently when I need to see anything like that I need an isolation transformer to verify that it (the spike) is from my measurements and not from the measuring equipment.
You mentioned that a zener diode was used in a test that failed...
Yes?
Did you measure the device within it's specifications?
I think Not.
If you compare your measurements against the data sheet you will find the part is OK and your understanding of how it "should" work needs some revision.
If you are asking about a clamp for a supply line or source or for an input then you will likely fare better by asking Mr Google about a "Voltage Clamp".
I did and this was my first observation for the search for "Voltage Clamp".
"About 3,240,000 results (0.23 seconds)"
and this:
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&ved=0CDcQFjAA&url=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FVoltage_clamp&ei=jNfpUPH1NdDVigLliYH4Bw&usg=AFQjCNEXwkyJXaou9eNdA7R9PO4cW8VmmQ&sig2=0IXYGyApBAuRqaTtUHX5lw&bvm=bv.1355534169,d.cGE was the first return from the search.
Wiki is generally the expert, having been written by the experts for the general public. Try reading it first. It helps a great deal to know which questions to ask before trying to address your concerns.

Bob
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

lemming

There is this tutorial by Grumpy Mike:

http://www.thebox.myzen.co.uk/Tutorial/Protection.html

I don't know if his previous comments detract from this?

oric_dan

I didn't see anyone mentioning Tranzorbs, they are specifically made for such pin protection,
and very common on industrial embedded controllers. Kind of a low-inductance, fast-acting
zener, with large power dissipation capability.

http://en.wikipedia.org/wiki/Transient-voltage-suppression_diode

On my own boards, I've been using simple 330 ohm [or so] series-Rs for years, and had
pretty good luck along the way.

DROBNJAK

How do you use these Tranzorbs? I've just had a look on Farnell.uk and all the listed ones have voltage protection in 30-60V range. Not exactly the voltage one uses with Arduino components.

Grumpy_Mike

You wire them across the supply. However they are not for the sort of spikes you have, they are for mich bigger ones with more area under the curve.

SirNickity

Some of the replies here seem a little harsh.  Certainly there's a misunderstanding on how zeners work, but honestly I've been there too.  Many of the introductory tutorials sort of paint a zener as a cheap and easy regulator, with very little mention of gradual knees and current dependence.  I had a sense that nothing in life is ever that simple, so there must be more to it.  Turns out there is.  Between "This is what a zener diode looks like" and the graphs in the latter pages of a datasheet, there's quite a void.  The information is there, you just have to know to look for it.

So, it seems to me if you're going to take the time to post a reply criticizing someone's lack of understanding, at least take the time to suggest a correct approach.  If you can't be bothered, just move on.  Thanks to everyone here that takes that extra step, though.  I for one appreciate it greatly.

oric_dan

#21
Jan 08, 2013, 11:30 pm Last Edit: Jan 08, 2013, 11:32 pm by oric_dan(333) Reason: 1
You can see here that transzorbs go all the way down to 3.3V.

http://www.digikey.com/scripts/dksearch/dksus.dll?vendor=0&keywords=transzorb

Download the datasheet, and read up. As already mentioned, they work similar to a
low-inductance, fast-acting zener, and the low-voltage devices are made specifically
for absorbing transients on data lines.

http://www.digikey.com/product-detail/en/SA5.0A-E3%2F54/SA5.0A-E3%2F54GICT-ND/2880343

DROBNJAK

#22
Jan 09, 2013, 03:33 pm Last Edit: Jan 09, 2013, 03:37 pm by DROBNJAK Reason: 1

Some of the replies here seem a little harsh.  Certainly there's a misunderstanding on how zeners work, but honestly I've been there too.  Many of the introductory tutorials sort of paint a zener as a cheap and easy regulator, with very little mention of gradual knees and current dependence.  I had a sense that nothing in life is ever that simple, so there must be more to it.  Turns out there is.  Between "This is what a zener diode looks like" and the graphs in the latter pages of a datasheet, there's quite a void.  The information is there, you just have to know to look for it.

So, it seems to me if you're going to take the time to post a reply criticizing someone's lack of understanding, at least take the time to suggest a correct approach.  If you can't be bothered, just move on.  Thanks to everyone here that takes that extra step, though.  I for one appreciate it greatly.


@SirNickity: Thanks. The original purpose of this forum is for newbies to ask questions. Even if one knows answer to some questions, there is no room for arrogance, because he/she doesn't know the answer to all the questions in the universe.

Googling around doesn't always answer the questions, particularly if one is only guessing what is the right jargon to use.

DROBNJAK


There is this tutorial by Grumpy Mike:

http://www.thebox.myzen.co.uk/Tutorial/Protection.html

I don't know if his previous comments detract from this?


@lemming: pure gold! Thanks for that.

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