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Old 5th April 2004, 07:50 PM   #1
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Default schottky vs. soft/fast recovery diodes

Hi,

Are schottky diodes always preferred to soft/fast recovery or stealth diodes in rectifiers as long as there are available schottky diodes with required maximum repetitive reverse voltage ?

Thanks...

MB
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Old 6th April 2004, 01:14 AM   #2
ClassD is offline ClassD  Australia
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Schottky diodes:

+ Low forward voltage
+ Fast recovery time
- Not available in ratings higher than about 60V
- high leakage current

Soft/Fast Recovery diodes:

+ Fast Recovery Time
+ High voltage rating
+ Low leakage current
- High foward voltage

Choose whichever is going to be more efficent in your circuit.
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Old 6th April 2004, 01:19 AM   #3
Magura is offline Magura  Denmark
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There is a noise aspect to this as well. Wich makes more noise?? It seems to differ from application to application.


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Old 6th April 2004, 04:38 AM   #4
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Seems that there are manufactureres who have managed to get round the low voltage limitation with Schottky diodes :

www.cree.com

I bought some 600V 1A ones from an online retailer a while back but have not tried them out yet.

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Joe Ling
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Old 6th April 2004, 05:14 AM   #5
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Are they expensive??

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Old 6th April 2004, 07:03 AM   #6
ClassD is offline ClassD  Australia
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Quote:
Originally posted by Magura
There is a noise aspect to this as well. Wich makes more noise?? It seems to differ from application to application.


Magura

Well the 'Soft Recovery' diodes were specifically designed to reduce switching noise. They have a gradual turnoff which rounds off the switching current waveform. This results in a lot less RF noise, with a small sacrifice in efficency.

However if you are using the diodes in a standard 50Hz bridge rectifier then there will really be no diffrence because the frequency is so low.
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Old 6th April 2004, 07:27 AM   #7
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Quote:
- Not available in ratings higher than about 60V
MBR10100

Quote:
Well the 'Soft Recovery' diodes were specifically designed to reduce switching noise. They have a gradual turnoff which rounds off the switching current waveform. This results in a lot less RF noise, with a small sacrifice in efficency.
And in my understanding the schottky does this even better
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Old 6th April 2004, 11:28 AM   #8
ClassD is offline ClassD  Australia
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Oops, meant to write "generally not available over 60V".
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Old 6th April 2004, 12:11 PM   #9
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Default soft turnoff.

Quote:
Originally posted by ClassD
However if you are using the diodes in a standard 50Hz bridge rectifier then there will really be no diffrence because the frequency is so low.
I used to think so too. Get your scope out and have a look at the transformer secondary voltage under load. Zoom in to where the waveform is just starting to move away from the flattened peak and head toward zero again. As a slow diode recovers it will "snap" the reverse recovery current off suddenly, causing the transformer winding to ring somewhat. Fast, ultrafast and schottky diodes (and vacuum tube rectifiers for that matter) turn off more cleanly and don't "twang" the transformer winding and generate noise in the process.
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Old 6th April 2004, 12:46 PM   #10
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600V 1A ones cost USD1.60

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Joe Ling
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