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Old 20th September 2006, 10:42 PM   #1
novec is offline novec  Norway
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Default Schottky or ultrafast soft recovery diodes?

I'm putting together a 60V PSU for a classD amp, using 1kVA toroid and dual bridges. But what's best - Schottkys or ultrafast soft recovery diodes? (FRED?) The ones I'm looking at are the 43CTQ100 Schottky and the 60EPU02 FRED.

From the datasheets, all I can find is that the Schottkys have much higher junction capacitance and reverse leakage current, but I have to admit that doesn't tell me much. All I've picked up is that while FREDs have a fast recovery time (35 us for the 60EPU02), Schottkys have none at all, which makes them more suitable for very high frequencies. Is that right?

When that's sorted, there's the issue with bypass caps, snubbers and all that, which can get pretty complicated... But as far as I've understood, there's a substantial difference between the two types of diodes, in the way of filtering them.

EDIT: I'm planning on running BHC or Jensen 4-pole caps.
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Old 20th September 2006, 10:46 PM   #2
BWRX is offline BWRX  United States
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Try both and see which you like better.
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Old 20th September 2006, 10:50 PM   #3
novec is offline novec  Norway
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That's probably the best solution, but that means twice the designing work and twice the component cost... Which, considering I don't have any low cost electronics supplier nearby, will be atleast a couple of Benjamins. I know there are no absolutes in audio design, but I figured some of you have some experiences to share.
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Old 21st September 2006, 12:22 AM   #4
cerrem is offline cerrem  United States
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Some key questions ...
What is the current demand on this power supply?????
What value Caps/filtering is involved???

Chris
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Old 21st September 2006, 01:55 AM   #5
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Isn't there a problem with parelleling diodes, I thought that if you parellel two or more diode the one with the lowest on voltage will be the one doing all the work (basicly not sharing current with the other diodes)?
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Old 21st September 2006, 02:02 AM   #6
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I've had very good results from the ultrafast soft recovery diodes. I have used the HFA08TB60 diodes from International Rectifier, and the MBR860 from On Semiconductor. Both are very good, but I prefer the HFA diodes myself. Either work quite well and don't ring significantly even without bypassing or snubbing.

Cheers, Terry
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Old 21st September 2006, 02:18 AM   #7
Bare is offline Bare  Canada
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I'm under the understanding that one can simply use the "Diode 'of the week" downstream from yer Bridge
Thereby gaining ALL of that particular diodes benefits and only having to pay for ONE 'special' diode.

It's about using yer brain .. not just paying for unecessary parts :-)
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Old 21st September 2006, 02:36 AM   #8
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Hi Novec,

The HFA series diodes from IRF have soft recovery and fast recovery characteristics...
Meanwhile I do prefer EP series schottkys because I have seen the results better than HFA series in some high current applications, where switching noise was a significant contributor..and schottky's produce less switching noise than any of the high current UFR diodes during high current operation. The reverse leakage current of schottky's doesnot degrade any performance form in the application.

regards,
K a n w a r
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Old 21st September 2006, 05:54 AM   #9
Eva is offline Eva  Spain
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Any power diode will do for 50/60Hz rectification. Schottky and ultrafast diodes are strictly required for SMPS applications only, where they are driven from very low source inductances and are forced to commutate within 100ns or faster at very high dI/dt rates.

In 50/60Hz applications, the huge leakage inductance of the transformer and the mains line results in a very slow commutation process lasting 100us or so, thus the 1us reverse recovery period of a slow conventional diode is not enough to produce any reverse current peak (as opposed to what happens when commutation is forced in SMPS circuits, where you usually get a 50% 'If' reverse peak even with the best diodes). Read also about snubbers, there is a thread where I posted very interesting oscilloscope captures somewhere.
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Old 21st September 2006, 11:01 AM   #10
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Quote:
... posted very interesting oscilloscope captures somewhere ...
For the searchwise challenged: Fast Recovery rectifier diodes
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