fast bridge rectifier

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#4
MurrayP said:
it's to do with how fast it stops reverse conduction when reverse biased. Fast rectifiers create less noise in audio power supply rectifier circuits.
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Do they? - I would have imagined just the opposite?.

They are usually used in switchmode PSU's and line output fed supplies - anything that runs at a higher frequency. Generally you don't see them used as normal mains rectifiers.
 
#5
oops - please excuse my looseness with words - most fast rectifiers these days are also soft recovery. I equated fast with soft recovery. With fast soft recovery you don't tend to get the snap off effect that you do with conventional rectifiers. That can be beneficial even at 50Hz in reducing what is often heard as buzz in power supplies from the rectifier noise. That is the same noise that the small cap often placed across the bridge diodes similarly suppresses. I hope I'm not going to regret prolonging this - I wasn't after an argument - just a direction to any such diode pack.
 
#7
bridges

Nigel Goodwin said:
No argument, I was just asking - I'd never heard that before. I also thought the small capacitors across the rectifiers were to help prevent them being damaged by mains borne spikes?.
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Nope, I think the mains borne spikes are suppressed by line rated capacitors across the AC mains. The caps across the rectifiers are to supress the noise generated by the switching of the rectifier diodes and need not be mains rated.

Can't help you with the same package-- but for something that is relatively close check out the IXYS VBE models (figures 24, 74) here.
 
#9
The background of the music is much quieter with the fast rectifiers-it seems to make a sharper contrast(dynamic range) in the music.More difference between loud and soft passages. An old Audio Am article explained it. Less Rf floating in the curcuits.
 
#11
If it works, that's fine. I would have thought a normal bridge would only have to worry about switching 50-60 times a second. 🙂 Even in high/fast loading, I thought think a (or a few) decent sized cap(s) would do the job admirably. Are you still using it immediately downstream of an AC source/transformer, or somewhere else in the circuit?
Again, not criticising or arguing, but I'm curious because I'm a few weeks off requiring a bridge in a little project I'm doing; if a fast recovery bridge is going to help it, I'll get one.
 
#12
I was of the same opinion a long time ago. That capacitors would take care of most noise. Generally used .1 in parallel with .01 uf for minimal bypassing with a bigger electrolytic.Then I read Corey Greenbergs article on his preamp where he changed his diodes so I tried it on the Line Amp made by audio Alchemy and it sounded much quieter in the backgroundwith the other changes I've mentioned. Since then I've modded preamps and even a sony receiver and the effects are always the same. Kinda hard to find those types of diodes to use for Power Amp, which is why I've never tried.
 
#14
MurrayP, this part may be what you are looking for:
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Cherhit - that's exactly what I was after - many thanks! Now I just have to find a source!


Yes the caps are targeted to do the same job I think but it's always better to avoid creating the problem rather than supressing it afterwards I think,

best

Murray
 
#17
Well, sounds like you're onto a good thing; I will have to investigate. Just out of curiosity... were we all talking about caps on the AC side of the bridge, or the DC? I guess you could call sinewave voltage on the DC side noise, where the cap buffers it to close to rail (which is obviously the traditional approach), but are you guys talking about putting a cap on the AC side of the bridge? If you are, that's good... and I can see the benefit of a fast/soft bridge. I would think you'd need a cap on the DC side anyway. Yes? No?
 
#19
The caps will be even more effective if a suitable value resistor is used in series with each cap, probably in the 1 to 100ohm region, best set up with a scope more max damping of the RF ringing but it can be hard to trigger on. A cheaper method is a single series RC across the secondary winding as it's the RF ringing of the transformer leakage inductance/diode capacitance that you're really trying to stop. Four caps/resistors is probably better though.

A detailed view........http://www.hagtech.com/pdf/snubber.pdf
 
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