Ultrafast rectifiers ?

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youyoung21147

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Joined 2005
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#1
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 🙂
 
#2
youyoung21147 said:
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 ?
Click to expand...

Not only fast, but also soft-recovery.
---
They are in fashion 😀
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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.)
 
#3
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???????

Tony.
 
#9
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 ??
 
#11
Sch3mat1c said:
I'm missing something, what exactly is it about 8.33mS pulses that needs switching 10^5 times faster?

Tim
Click to expand...


Tim,

The Trr is REVERSE recovery time, it has no bearing on the forward conductance. Diodes that have no fast recovery take some time to turn of after the voltage across them reverses, this is the recovery time. The recovery often behaves oscillatory and that generates hf pulsels that can get into the supply. However, when you have a fast recovery, you can get one single sharp turn-off pulse which is also bad. Unless they are soft recovery: smooth, fast turn off is best.

This is the theory, and in smps applications, when the signal to be rectified is 100's of kHz or even a Mhz, this is measurable. Some people apparently feel they can HEAR it in audio as well, one more piece of audio folklore...

Jan Didden
 
#13
janneman said:


Some people apparently feel they can HEAR it in audio as well, one more piece of audio folklore...

Jan Didden
Click to expand...

Jan, did you never do the simple comparison tests ? Even I hear differences in power supply diodes. Differences, no more no less. I feel it is slippery to contribute the differences to the speed of the diode though....
 
#14
forr said:
I think Nelson Pass recomands the use of standard diodes.
Click to expand...


Not anymore 😉


Nelson Pass said:
We are currently using the ST Micro BYW99W-200, which is
a dual "high efficiency, fast recovery" 35 amp diode at 200
volts, and have been very happy with it.

It's remarkable for us to have converted to exotic rectifiers,
as we previously were very sceptical, but we did find a distinct
sonic improvement, and they also made it easier to meet
RF noise emission standards. 😎
Click to expand...

http://www.diyaudio.com/forums/showthread.php?postid=321830#post321830


And Mr. Carr suggests that "sonic differences are caused not only by the category of rectifier diode, but the manufacturer as well"

http://www.diyaudio.com/forums/showthread.php?postid=102326#post102326
 
#15
I think that using fast diodes put some requirement on all capacitance. Better do similar connection like following sheme example:
transformer -> ultrafast diodes bridge -> capacitance 24000uF -> capacitance 7500uF -> capacitance -> 2200uF -> amplifier itself

Reggards
Niki

EDIT: hehe, Peter Daniel like i say before - using of BYW or BYV fast Philips diodes are great advantage for sheme itself! 😉
 
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