:lol:
hi guys Im experiencing between the two diodes. Im confuse about them how do they differ in physical appeareances? and how to check a schottky diode using an analog meter?

And how they are used in a circuit? thanks.

POST PLS. GOD bless you all

 

Schottkey didodes have an much lower forward breakdown voltage.Thats all.They act as an nomal diode.And you check it the same way too.

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And the scottky is fast recovery, so useable in switchmode PSU as rectifier up to about 1MHz. (depending from type)

 

Schottky vs "standard" silicon diode

Schottky generally has lower reverse voltage max. You can easily find silicon diodes with 200-1400v ranges, while commonly schottky is 20v-60v.

Schottky is extremely fast recovery, even faster than so-called "fast recovery" silicon diodes. So you can use them in high frequency SMPS.

Forward voltage drop is lower. In silicon you get 0.6v-0.7v at rated current. In schottky you can get 0.3v which is great for SMPS.

Most schottky diodes look exactly the same is a regular diode.

if you want to test a schottky with an multimeter, set it to measure forward drop and measure the drop of the diode if its 0.3-0.4 its a working schottky. (or a burned silicon....)

 

Silicon diode: Use of P-doped silicon and N-doped silicon to make a P-N junction that causes the blocking effect

Schokky diode: Use of (normally) P-doped silicon bonded to metal. The junction effect is at the metal connection and it is because only one doped-tpye of silicon is used you end up with the lower on-state

seems everyone is champion Schokky's her, there is a slight disadvantage with them with nice high-power electronics in that their reverse recovery is alot higher then a standard diode when operated as a free-wheel diode.

This comes from their ohmic connection

Saying that though Schokky (SiC devices) are comming in, although the reverse recovery is worse the lower on-state losses is very attractive

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I think i have an scottkey rectefier someware.Its two powerful diodes in an TO-220.There is much less heating than an normal diode.I cod run 10A trough it and it only got slitly warm.

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Il give you shocking experience.

 

Styx, I think I have heard this same statement from you in the past. Can you cite evidence for this claim? My understanding is the exact opposite (and a Google search confirms this).

__________________
Ron

 

Sure will do.
I am not allowed to use Schokky diodes anywhere in my control cct at work for one thing.

But the power electron side of thing's is in my power-electronic book on my desk at work.


The only exception to the rule of "no schokky diodes in free-wheel" is with SiC since there are some extra benefits from SiC

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Once a problem is realised, the rest is just details

 

Here's a quote from International Rectifier:
"This explains the Schottky diode's lack of reverse recovery, making it ideal for high frequency applications."
A Google search for "schottky reverse recovery" yields several similar hits. Make sure you spell "Schottky" right, or you won't find anything.
I don't think a decree from your boss is a "cite". How about one from your power-electronic book on your desk at work?

__________________
Ron

 

Schottky diodes typically have a higher reverse leakage current.

Typically Schottky diodes have a forward voltage which rises more in response to current than a std rectifier. But it's a bit of an apples-to-oranges comparison, it depends on the junction area.

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Power Electronics: Converters, Applications and Design. 2nd Edition
Mohan/Underland/Robbins
ISBN: 0-471-58408-8

Ch20: Power diodes – Schottky diodes.

Not quoted but summarised

Advantage:
Speed (thus lower switching losses)
Low forward volt drop (thus lower on-state losses)
Low voltage overshoot at turn-off

Disadvantage:
Silicon based Schottky’s limited to 200V reverse blocking (a P-N can block 1200V for a doping of 10^4 cm-3)
The reverse recovery is comparable to the reverse-recovery of a P-N diode (extreamly unexceptable)
Ther reverse leakage is worse for a comparable P-N diode



SiC have solved the reverse blocking (can now get 1200V) but that is only due to the SiC being able to support kV’s of voltages

--EDIT--
corrected a mistake

__________________
Nothing is impossible.
Once a problem is realised, the rest is just details

 

Styx, reiterating: this is the statement I am questioning. You seem to be sidestepping it. I totally agree about all the other properties of Schottky diodes that you listed. Can you support the above quote with something from the book on your desk, or some other source?
What does this mean? Leakage is measured in amperes, and reverse recovery is measured in seconds.
Styx, I'm not picking on you - I just don't think we should be disseminating misinformation here. If I am wrong, I'll be happy (but not too happy) to admit it.

__________________
Ron

 

Errr post above yrs my me full book refernce ISBN provided an all.
Well reverse recovery is actually measureed in AMp-seconds

That aside tho.
The full quote is

Thus I stand by the fact that Schottky's have a reverse-recovery problem just like a standard diode. The only difference is the source of this reverse -recovery charge.

in a PN it is the stored charge (ie hte diode acting like a capacitor) and in a Schottky it is behaving like a short-cct while the volts across the device a building up[/quote]


This has been taken from the 2nd edition of the "power electronics bible" and I have also confirmed it is in the 3rd edition (which is less then a year old)


So The fact that they do exibit reverse-recovery (that is comparable to the reverse recovery of a standard PN) means no advantage or dissadvantage.

The on-state losses gives a fantastic advantage, but the increase reverse leakage will increase the losses during the portions where the Schottky is blocking

Yes in the last few post mixing terminology a bit (soz) but that is the definitive statement that backs my 1st post in this thread abt the reverse-recovery of Schottky diodes

__________________
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Once a problem is realised, the rest is just details

 

I experimented using some in a distortion effect, I thought that they sounded better than silicon as clipping diodes, though i'm sure they can do more in other situations :lol:

Mine appear quite differently actually, they are blue with a white stripe on them, but i'm sure a lot of them look like ordinary diodes.

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Will have to make do with myspace now I guess...

 

Just checking:

So by styx's assertion Schottky diodes should not be used as freewheeling diodes because their internal parasitic capacitance is actually GREATER than the equivalent reverse recovery loss of a standard silicon.

i just want to make sure of this point for myself. I'll start ripping them out of my SMPS if its true.