Author Topic: What are schottky diodes?  (Read 1576 times)

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What are schottky diodes?
« on: August 19, 2010, 02:05:05 PM »
I pulled some out of a board I salvaged from what dead electronics I don't even remember. The board had the part code so I looked it up online and there was the name. They look strange and I've not come across them in a part roster for anything I've ever built. Are they even intended for an audio path?


oldschoolanalog

Re: What are schottky diodes?
« Reply #1 on: August 19, 2010, 02:58:41 PM »
Google is your friend.
Check it out...
(Link)
« Last Edit: August 19, 2010, 03:06:41 PM by oldschoolanalog »
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edvard

Re: What are schottky diodes?
« Reply #2 on: August 19, 2010, 03:01:36 PM »
They're pretty much like normal diodes, except the forward voltage is in the range of 0.15 -0.45 volts depending on what kind you have.
Compare to Silicon at 0.6-1.7 volts and Germanium at 0.3 volts.
I hear the reverse leakage is worse than regular diodes, though.
All children left unattended will be given a mocha and a puppy

Re: What are schottky diodes?
« Reply #3 on: August 19, 2010, 04:16:06 PM »
From what that link says, they seem to be described as the universal purpose diode.
Wth is "leakage" though??


newfish

Re: What are schottky diodes?
« Reply #4 on: August 20, 2010, 12:39:44 AM »
Try 'em.

Why not build a Distorion + on a breadboard and spend a happy hour or two substituting the clipping diodes?

Last Op-Amp distortion box i built had some non-standard diodes in, and sounded excellent.

EDIT : Yes, i used 'whatever sounded best out of the drawer' - and they *are* the blue / black Schottky type.
To my ears <subjective alert here...>, less 'fizzy' than when compared to the usual 1N4... Silicon types, without the massive volume drop of Ge devices.
« Last Edit: August 20, 2010, 03:19:50 AM by newfish »
Happiness is a warm etchant bath.

edvard

Re: What are schottky diodes?
« Reply #5 on: August 20, 2010, 02:08:46 AM »
Leakage is current that goes the 'wrong' way in a diode or transistor.
All semiconductor devices leak to some degree, especially older germanium devices.
Apparently Schottky diodes work like they do because they are built like MOSFET gates.
That gets you lower forward voltage and very fast recovery, but it's leakier than a straight P-N junction.

Homework:
http://en.wikipedia.org/wiki/Schottky_diode

Like newfish said, try 'em, maybe you'll like 'em...
All children left unattended will be given a mocha and a puppy

Re: What are schottky diodes?
« Reply #6 on: August 20, 2010, 04:41:40 AM »
Ah ok, I thought leakage meant they were leaking power or signal bandwidth.
The explanation still adds another question to my mind.
Do parts that leak have a shorter lifespan in contrast to parts that don't?


newfish

Re: What are schottky diodes?
« Reply #7 on: August 20, 2010, 04:55:23 AM »
i wouldn't imagine there's any issue with component longevity at the voltages we as stomp-boxers are dealing with.

I have a 15-year old hybrid pre-amp on my bench.  The Op-Amp / buffer side of things is great - it's the valve power supply that's failed.
Happiness is a warm etchant bath.

R.G.

Re: What are schottky diodes?
« Reply #8 on: August 20, 2010, 05:15:17 AM »
Shottky diodes are literally half a normal diode. They are a metalization layer put on a doped semiconductor region in a way that causes a similar forward/reverse diode operation. The advantage is very low forward drop and very low capacitance and stored charge, so they are also very fast at turning off. They were first popular for switching power supplies where their low forward drop and fast turn off ate up less wasted power.

Leakage is another issue. In a perfect capacitor or diode, there is absolutely zero reverse current flow. It's just like a faucet - leakage is stuff dripping through where it's not theoretically supposed to. And like a faucet, leakage is primarily a waste. A certain amount of leakage can be tolerated, just as you can usually wait a few days to get a new faucet washer. But low leakage is good (with the notable exception of the Millenium bypass!  :icon_lol: ) in almost all cases.

Leakage per se does not shorten life. The secondary effects of leakage, like heating, may do that. Leakage which is notably worse than you expected in the device is an indication that the device is damaged in some way. Leaky capacitors may fail soon. Leaky diodes may fail and also waste the power  you're using. Leaky transistors the same. But if you have expected the leakage and provided in the design for the expected amount, leakage does not necessarily shorten device life.

HEAT shortens device life. Thermal cycling (hot-cold-hot-cold....) shortens device life. Leakage only as it contributes to those two.
R.G.

The music world seems to be a three-way race between the princess and the pea, the blind men and the elephant, and the emperor's new clothes.