| MurrayP |
HI,
can anyone here point me toward a fast recovery bridge rectifier in the same package as the standard 25A/35A metal packages please?
thanks
Murray |
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| Dr. Apathy |
| What is the purpose of a rectifier recovering quickly, and what does it recover from? |
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| MurrayP |
| 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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| Nigel Goodwin |
| quote: | Originally posted by MurrayP
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. |
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. |
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| MurrayP |
| 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. |
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| Nigel Goodwin |
| 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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| lgreen |
| quote: | Originally posted by Nigel Goodwin
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?. |
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. |
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| cherhit |
MurrayP, this part may be what you are looking for:
http://www.diotec-usa.com/35dbps.PDF
Problem is, though, I don't think you can buy these through regular distributors, and their minimum order is probably more than one person would be willing to buy. |
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| Lee1234 |
| 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. |
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| Lee1234 |
| Makes a big difference in preamps. Never tried it in power Amps so I don't know there. |
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| Dr. Apathy |
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. |
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| Lee1234 |
| 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. |
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| testlab |
| I just finished a board with HEXFRED's in a bridge configuration. It is going to fab this week. |
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| MurrayP |
| quote: | | MurrayP, this part may be what you are looking for: |
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 |
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| Lee1234 |
| Mike percy has them now. You guys made me look. |
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| Dr. Apathy |
| 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? |
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| MurrayP |
4 film caps - say 0.047uF 200V - one in parallel with each diode of the rectifier. It's pretty standard practise,
M |
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| sbrads |
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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| Duck-Twacy |
I have these Ixys VBR 55-06N07 for my Aleph amp.
http://www.ixys.com/l363.pdf
Is it still benificial to put caps (snubbers) on them? The PS also has a pi filter (88 mF - 2,2 mH - 132 mF) |
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| crippledchicken |
| i've had good luck using the stealth diodes from Fairchild building rectifiers also. ;) |
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| dmfraser |
If you're getting rectifier noise in the audio your ground layout is bad. I design amps over 1000W with 100db and better signal to noise ratios and never get rectifier noise in the audio. None. Nothing but the hiss from the electrons bumping into each other.\
You have to make sure that the loop of rectifiers/capacitors is a separate loop from capacitors/audio. If the ground between the amp and the filter caps shares any conductor with the rectifiers, you will get rectifier noise.
In a bi-polar power supply, the transformer center tap must go directly to the common point between the two filter caps. And this common point must be very, very heavy. Then the ground from the amplifier connects there. This makes it so you have separate paths for the current that charges the capacitors and the path that supplies power to the amplifier.
Any deviation from this will degrade the s/n ratio. |
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| Menno Keizer |
Dan Fraser,
Can this be solved by using two separate bridges and separate transformer windings? (in the bi-polar case)
Menno |
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| dmfraser |
No, the configuration must be correct. The current path from the rectifiers to the filters cannot share any conductors with the current path from the filters to the audio circuitry. The only place where this cannot be avoided is between the ground pins of the two capacitors assuming you are doing a balanced power supply. In this case, the conductor between the ground leads has to be very heavy. Like 8 gauge wire or a PCB trace at least 12mm wide.
To this conductor the center tap connects. The audio ground will connect between these two filters as well.
This point is also where the "ground" lead of your speakers must connect. Not at the amplifier.
I sometimes also put .01 uFd caps across each diode in thebridge to soften the spikes though in reality, if the grounding is done right you won't need them.
Also, the wires from the bridge must go directly to the capacitors. Then the power wires to the audio circuit comes from the capacitor. This forces all the rectifier current through the capacitors. DO NOT connect the bridge output to your circuit then run wires to the cap. Because that would end up with audio power sharing a conductor with rectifier current.
The simple rule is that the rectifier/filter current loop cannopt share any conductors with the filter/load current loop. Similarly, the speaker ground current must NOT share any conductors with the lower level audio signals. If they do, you will get spurious oscillation and coloration of the sound. |
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| Dr. Apathy |
| Caps across the DC side of the rectifier are common as mud (and I agree with using a few in parallel, for better temperature dispersion, among other things), but are the original posts talking about putting caps over the AC side of the rectifier? I always thought caps on the DC side were just for voltage smoothing, that's all. Maybe noise is another word for it... |
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| dmfraser |
I mean on a bridge 4 caps, one in parallel with each diode. About .01µFd at twice the DC output voltage of the power supply. Say 200V caps. Ceramic disc are file as they absorb RF better than film caps.
By filter caps I mean the big electrolytic caps. |
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