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Old 11th October 2005, 07:07 PM   #1
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Question Ultrafast rectifiers ?

Hello,

I'm planning to build a PSU for my future chip amp (surely a GainClone) and I am wondering which rectifiers I should use.

I plan to order some samples from OnSemi to compare but I ask here what kind of rectifier I should use :

I know they need to be fast, 35ns is a good value.

But concerning the rest I don't know. Why do people like MUR860 diodes more than the other ones ?

I was thinking that 8A for 2 amplifiers isn't enough.

So why not use 16A or 30A ? Are small ones more "refined" ? Or is bigger better ?

Concerning the rating, should it be adapted to the circuit or is it better to use higher voltage ratings ? (eg. 200V or 600V)

Finally are there any other parameters to take into consideration when a choice has to be made ???

I'm a little lost so every comment is welcome
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Old 11th October 2005, 07:40 PM   #2
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Default Re: Ultrafast rectifiers ?

Quote:
Originally posted by youyoung21147
Hello,

I know they need to be fast, 35ns is a good value.

But concerning the rest I don't know. Why do people like MUR860 diodes more than the other ones ?
Not only fast, but also soft-recovery.
---
They are in fashion
-----
Why not use schotky-diodes. ? Faster than ultrafast and absolutely soft-recovery. plus low-losses. OK, if you need more than 100V rated diodes then schotkies are not first choice. (altough 200v ones are becoming more availlable and 600&1200V SiC-schotkies are also availlable.)
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Old 11th October 2005, 09:35 PM   #3
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The MUR860's are 50ns but have very high (600V) ratings... go to www.farnell.com and do searches on soft recovery and ultra fast recovery, you should get a large selection some as fast as 20ns whilst still handling the 8A of the MUR860's..... not sure on the voltage.....pobably 200V max for that speed...

as for which ones work well???????

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Old 11th October 2005, 10:51 PM   #4
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Default ok, check these:

Check BYW29E-150, BYW29E-200, BYV-series etc.
Right now I'm with first type on my Gainclone and with similar for my DeathOfZen-Class-A amp and I'm very satisfied with results.
Great diodes - ultra fast, fast recovery etc.

Best Reggards
Niki / Bulgaria
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Old 12th October 2005, 07:24 AM   #5
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Default Re: Re: Ultrafast rectifiers ?

Quote:
Originally posted by mzzj
also soft-recovery.
That is actually the important bit.


Quote:
Why not use schotky-diodes. ? Faster than ultrafast and absolutely soft-recovery. plus low-losses
Any time your required voltage is low enough these are hard to beat...

dave
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Old 12th October 2005, 11:00 AM   #6
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Default Re: ok, check these:

Quote:
Originally posted by bezobraznia
[snip]- ultra fast, fast recovery etc.

Best Reggards
Niki / Bulgaria

... which is the same of course. Ultra-fast refers to the recovery, NOT to the forward path.

Jan Didden
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Old 12th October 2005, 11:46 AM   #7
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Default Re: Re: Ultrafast rectifiers ?

Mmmm Interesting !

: Not only fast, but also soft-recovery.


==> How do you quantify "softness" of diodes ?

Is it worthy to use some 16A or 30A for more "safety" ?
Is it better to use 600V instead of 200V ?
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Old 12th October 2005, 11:50 AM   #8
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10x for correction... but You follow my point
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Old 12th October 2005, 07:37 PM   #9
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I found some "Ultrasoft" rectifiers at OnSemi : the MSR1560.

Rated 600V 15A
They are said to be ultrasoft, and have a pretty good 45ns Trr.

I assume they are good candidates aren't they ?


I also found some Shottky rectifiers : MBR40250.

They have a good 35ns Trr and are rated 40A 250V

They are oversized, but I assume it doesn't matter.


Apart from price, what model would you recommend me between those ?

Are there measurable parameters apart from Trr that would help me guess which or which part is the best ??
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Old 12th October 2005, 07:56 PM   #10
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I'm missing something, what exactly is it about 8.33mS pulses that needs switching 10^5 times faster?

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