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Choosing the right diode for a given function

Choosing the right diode for a given function

(OP)
When making a bridge, it's obvious that I have to choose a diode based on their current and voltage ratings.

But for other functions, like
Logic
Safety
Switching
Etc

What is a germanium diode for ?
Shottky barrier ?

How do I choose a diode to put next to a relay, and why ?
When exactly do I use switching ? And why not other types

I don't see that on books: a full comparison chart showing type and function. Can't find useful tips by long age engineers around the web...

RE: Choosing the right diode for a given function

'germanium diode'
E.g. 1N34A, low Vf, about 0.3v. Ideal for 'crystal radios'.

'Schottky'
Fast.

'switching'
E.g. 1N914 1N4148. General purpose. Logic circuits.

You could browse the catalogs (e.g. Digikey) for diode PNs, and then review the data sheets. This should lead to some very good info about the characteristics and applications.

RE: Choosing the right diode for a given function

And, of course, Zener Diodes. Used as (crude) voltage stabilizers and overvoltage protection/limiters. Please note that the German word Zehn (meaning "ten") has nothing with Zeners to do. Zeners are available over a wide voltage range - typically from 3.9 V up to 47 V or higher. Best dynamic performance at around 5 or 6 V. Rather low tempco there also.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Choosing the right diode for a given function

You can by bridges instead of building one yourself. Search Digi-Key for them.

RE: Choosing the right diode for a given function

Wait until you have to pick a ferrite bead... or even worse, properly select a capacitor sadeyes

Dan - Owner
http://www.Hi-TecDesigns.com

RE: Choosing the right diode for a given function

If I want to build a hammer - what material shall I use? There are different metals, different plastics - or should I use some ceramic material - and lots of natural stuff like bone, wood, perhaps concrete? I need a book that gives me some guidance on the matter. Is there such a book?

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Choosing the right diode for a given function

The diode is put next to the relay to protect the drive circuit from the voltage spike that can result when the coil is deenergized. V=Ldi/dt.

Z

RE: Choosing the right diode for a given function

(OP)
Many of you might be reading "Mechanical" on my profile. I'm trying to change that to Control Engineering, currently emphasizing on power circuits, like transistor or triac based switching supplies
I've got a lot to learn, but I'm not THAT noob.


Quote:

TO: mcgyvr,
I've enjoyed both articles. They answer the germanium and schottky questions, and give many application examples. Despite that, they seem oriented to those who Already know the diodes they want. I'm looking for something different. As if I had a target application, and I need the tool. And more important: common usages

Quote:

'germanium diode'
E.g. 1N34A, low Vf, about 0.3v. Ideal for 'crystal radios'.
'Schottky'
Fast.
'switching'
E.g. 1N914 1N4148. General purpose. Logic circuits.

Very good answer. I like that you gave a couple of examples and an ideal application on the first matter


Quote:

The diode is put next to the relay to protect the drive circuit from the voltage spike that can result when the coil is deenergized

This answers the "Why" part of the question. Keep going.

Quote:

TO: Skogsgurra,

Thanks for the Zener clarification. That responds a part of my quest. And I think it's enough about zeners. Curious examples of zener usages are abundant on the web

Your book question is a valid question. An intelligent one, in my opinion (although I don't know if you were sarcastic).
There may not be a book detailing the materials (for that there's google), but a table telling the basics of the available materials and their quirks should exist. That's what I'm looking for.



So, looking at the following areas, what diodes should I look for:

-Logic
-Safety
-Switching
-AnythingIMightBeMissing

Safety and switching may already be answered, but enriching the answers is welcome.

I'm also looking for those 'tips' that old cougars from the electrical world might add

I repeat the question:
When exactly do I use switching ? (A brief list with examples would be great as an answer)

What is the practical difference between schottky and german ?

ALSO IMPORTANT: Personal notes regarding practical usages and your experiences are welcome

RE: Choosing the right diode for a given function

german? Do you mean germanium verse silicon?

Germanium are an older type of diode that sports a much lower forward voltage drop at the expense of being much slower and more temperature sensitive.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Choosing the right diode for a given function

Schottky diodes are the silicon alternative to germanium.

As for books, there are design books. This is not a tutorial site. Anyone who goes into this much detail about diodes might as well have written a book chapter. No one starts off knowing what all the diodes are and when to use them. This is something that you learn on the job, as each design invariably has unique requirements, which is why there are dozens of different diodes.

TTFN
I can do absolutely anything. I'm an expert!
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

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