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Old 24th March 2003, 09:02 PM   #101
rljones is offline rljones  United States
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Have any of you compared the sonic differences between GaAs Schottky Diodes, regular Schottky Diodes, FREDs, and HiPerFRED Epitaxial Diodes? Would one type be better for rectifying a power supply?

(such as those at http://www.ixys.com/appasp/newparts.asp )

Also, I see data that shows the HiPerFRED Epitaxial Diodes turn on at 30 to35 nS. Are the Schottky's as fast (I don't seem to see speeds typically listed for them)?

Thanks, Robert
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Old 24th March 2003, 10:58 PM   #102
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Default IT'S A GaAs.

Hi,

Quote:
Have any of you compared the sonic differences between GaAs Schottky Diodes, regular Schottky Diodes, FREDs, and HiPerFRED Epitaxial Diodes?
Interesting point you raise here.

Personally I never tried the GaAs (Gallium Arsenide, I think) Schottkys, most of the time I prefer the common Schottkys though..they seem to exhibit the best behaviour for audio use and are the best sounding I tried so far.

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Old 24th March 2003, 11:12 PM   #103
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Speed isn't relevant in linear power supplies, except that it may exagerbate ringing effects in the inevitable inductances in the cicuits. Soft recovery is more important; Schottky rectifiers should be inherantly 'soft', but there may be other issues.
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Old 25th March 2003, 09:26 PM   #104
rljones is offline rljones  United States
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I came across data on the Vishay web site that indicated their Schottky diodes had speeds of 5ns as compared to typical HiPerFREDs wtih 30 to 40ns.

I have no idea whether speed is any issue; but I am curious as to the sonic differences among the various types of devices.

Another related question is, are snubber circuits necessary for these 'soft recovery' types as compared to standard silicon diodes?
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Old 26th March 2003, 12:57 AM   #105
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Hi,

Quote:
I have no idea whether speed is any issue; but I am curious as to the sonic differences among the various types of devices.
Your general assumption that Schottky diodes are superior to Freds and hexFreds seems correct to me.

Quote:
I have no idea whether speed is any issue; but I am curious as to the sonic differences among the various types of devices.
Generally speaking, I think speed always is an issue.
One reason I stick with vacuum state devices is their inherent speed.

Quote:
Another related question is, are snubber circuits necessary for these 'soft recovery' types as compared to standard silicon diodes?
Considering only the forward fed signal I wouldn't care about that too much, you can make them dissapear easily.
Howerver, if you care about what is thrown back into the mains (and you should) , snubbers are a godsend.

So to answer your question, I would put them in.

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Old 26th March 2003, 01:46 AM   #106
rljones is offline rljones  United States
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Next question, if snubbers are a good idea, a capacitor or an RC style snubber for soft recovery types?

Another piece of data I'm noticing from the spec sheets are junction capacitance. Most of the Schottkys are 40-50V seem to have about 115pF; many of the FREDs (like BYV32 have about 45pF); the GaAS Schottky from IXYS has 22pF for the 15A/180V device. So, is this capacitance significant? (Please excuse my ignorance; I'm not EE educated.)

Thanks, Robert
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Old 26th March 2003, 01:56 AM   #107
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Hi,

Quote:
So, is this capacitance significant? (Please excuse my ignorance; I'm not EE educated.)
I don't think so.

Please feel free to ask to your heart's content, you may not be aware of it but it often advances the state of the art more than talking to anchored engineers...

Cheers and thank you for being an investigating individual,
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Old 26th March 2003, 04:00 AM   #108
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Default About Shottky diodes......

The reason that they do not have the reverse recovery problem is that they do not use any minority carriers. There are lots of other ways semicon makers come up with to shorten the lifetime of the charge held by the minority carriers.

Comparing capacitance figures between Shottky diodes and soft-recovery types might not be a fair comparison.

Jocko
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Old 1st April 2003, 07:27 PM   #109
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Default high speed diode data

Some more info on high speed diodes. These are written from the standpoint of switching power supplies but the use of snubbers is relevant to reduction of RF noise in 60 Hz power supplies.

http://www.e-insite.net/ednmag/archi...97/03DI_03.htm

http://www.maxim-ic.com/appnotes.cfm...mber/849/ln/en
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Old 2nd April 2003, 08:38 PM   #110
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rtjones
Quote:
the GaAS Schottky from IXYS has 22pF for the 15A/180V device.
Are you talking about the DGS20 series rated at 17A? Has anyone any thougths on the newer higher voltage parts? What is the consensus on the dual unit diodes and bridges as compared to the discreet single units, is there any benefit to having the parts on the same silicon as opposed to matching them? Will the heat be an issue in a typical Class A application with sufficient heatsinking?
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