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Old 12th October 2005, 08:04 PM   #11
jan.didden is offline jan.didden  Europe
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Quote:
Originally posted by Sch3mat1c
I'm missing something, what exactly is it about 8.33mS pulses that needs switching 10^5 times faster?

Tim

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
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Old 12th October 2005, 09:22 PM   #12
forr is offline forr  France
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I think Nelson Pass recomands the use of standard diodes.

~~~~~~~ Forr

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Old 12th October 2005, 10:19 PM   #13
jean-paul is offline jean-paul  Netherlands
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Quote:
Originally posted by janneman


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

Jan Didden
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....
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Old 12th October 2005, 10:58 PM   #14
Peter Daniel is offline Peter Daniel  Canada
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Quote:
Originally posted by forr
I think Nelson Pass recomands the use of standard diodes.

Not anymore


Quote:
Originally posted by Nelson Pass
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.
http://www.diyaudio.com/forums/showt...830#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/showt...326#post102326
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Old 12th October 2005, 11:07 PM   #15
bezobraznia is offline bezobraznia  Bulgaria
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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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Old 13th October 2005, 09:21 AM   #16
Nordic is offline Nordic  South Africa
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Hi I'm looking through my rummage bins for diodes to rectify 6Vac 1A supply, to drive a .1A fan and some LEDs...

Only ones I can find 4 of is FR104...
I looked up the datasheet but it confuses me...
It says maximum reverse voltage 400V but maximum forward voltage 1V, does this men one cn only use these diodes on 1Vac?
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Old 13th October 2005, 12:02 PM   #17
analog_sa is offline analog_sa  Europe
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does this men one cn only use these diodes on 1Vac?

Of course not. It means that the forward biased drop will not exceed 1v at max current.
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Old 15th October 2005, 07:46 PM   #18
jan.didden is offline jan.didden  Europe
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Quote:
Originally posted by analog_sa



Of course not. It means that the forward biased drop will not exceed 1v at max current.

... or, said in another way, they need up to 1V across them before they start to conduct into a load that draws an amp...

Jan Didden
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Old 15th October 2005, 07:47 PM   #19
jan.didden is offline jan.didden  Europe
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Quote:
Originally posted by janneman



... or, said in another way, they need up to 1V across them before they start to conduct into a load that draws an amp...

Jan Didden


... or said in yet another way, the dynamic forward resistance may be up to an ohm..

Jan Didden
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Old 16th October 2005, 05:52 AM   #20
Nordic is offline Nordic  South Africa
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Yep, I noticed they dropped the power quite a bit (well by a large margin considering the total value of this small winding)...
Don't know if its them or the fan, but it is makeing noise on the amp windings.... tried connecting a 100R and 100ufd cap in parallel with it.. no difirence..
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