[silent:arts]

Benefit of schottky rectifiers in linear PSUs ???
« on: August 27, 2009, 02:53:31 AM »
Svart?  :) :) :)


[silent:arts]

Re: Benefit of schottky rectifiers in linear PSUs ???
« Reply #1 on: August 27, 2009, 03:03:36 AM »
GDIY51PSU Schematic

The power supply looks like it will require a transformer with multiple windings, not easy for most folks to get unless you have a source for those too.  I know it's too late for change suggestions however.  I would suggest that people use schottky(or any soft/fast) rectifiers and not use the caps parallel with the diodes.  Attempting to snub the diode snap will just shift it's power to a higher frequency making it harder to shield and more prone to leakage.

any suggestions / links for your preferred rectifiers? I'm new to schottky.

Schottkys are majority carriers so they have a much faster recovery and they have much lower forward voltage drops.  Standard P-N junction diode's reverse recovery current when snapping off causes EMI(the reason for the capacitor shunts).  Schottkys don't have this and are much more EMI quiet.

out of interest:
we are talking about a linear PSU, 50 / 60 Hz frequency at the rectifier.
all I could find about Schottkys the last hour via google / wikipedia etc is they are good for switching PSUs at high frequencies  ???
is there really an advantage in the schematic I posted?

Lower frequency=more power generally.

Tubemooley

Re: Benefit of schottky rectifiers in linear PSUs ???
« Reply #2 on: August 27, 2009, 05:07:05 AM »
This is off-topic but I think you will want to know..... I have it on good authority that the TL783 device is horrible and to not use it. I can put you in touch with the engineer who has told me this. It is Steve Hogan, former VP of Engineering at Jensen Transformers until about 1993. I just met with him in July in California. We were looking at a 2-channel mic pre box he was "fixing" for a client. It was a discrete transistor design. They used the TL783 regulator in there. He says it sucks. And he said why but I can't remember that part. He can be reached by e-mail but it may take him a couple of days to reply. Please contact me if you want to look into this further. E-mail me at tubemooley_at_yahoo.com. Just trying to help. DANA.

[silent:arts]

Re: Benefit of schottky rectifiers in linear PSUs ???
« Reply #3 on: August 27, 2009, 05:15:20 AM »
Hi Dana,

the TL783 sucks when doing a short while measuring  ;D
it is in the D-AOC high voltage supply, like in Gyrafs G9 - haven't heard of any problems yet.

Tekay

Re: Benefit of schottky rectifiers in linear PSUs ???
« Reply #4 on: August 27, 2009, 05:55:20 AM »
Audiofools are using schottky's like BYV27 in their psu's. It's all about spikes. 10nF in parallell with standard diodes will also lower the spikes. Don't use caps over the schottky's as it will be worse instead. BYV26E is a high voltage schottky.
Thomas "TK" Kristiansson
----------------------------------
"The Sound Is In The Iron"
www.vintagedesign.se  www.tkaudio.se

tv

Re: Benefit of schottky rectifiers in linear PSUs ???
« Reply #5 on: August 27, 2009, 06:07:00 AM »
Audiofools are using schottky's like BYV27 in their psu's. It's all about spikes. 10nF in parallell with standard diodes will also lower the spikes. Don't use caps over the schottky's as it will be worse instead. BYV26E is a high voltage schottky.
Wasn't MUR860 the "one"?
If you sprinkle when you tinkle, please be neat and wipe the seat.

Kingston

Re: Benefit of schottky rectifiers in linear PSUs ???
« Reply #6 on: August 27, 2009, 06:10:01 AM »
BYV26E is a high voltage schottky.

In this supply we're not really interested in high voltage as a limitation, but high current.

A tried and tested schottky, and most importantly cheap option would be:

100V, 3A, MBR3100RLG or for lesser currents,
100V, 1A, MBR1100G

I think most stores have them.

[silent:arts],
If you remove those useless (or even harmful) rectifier caps, there's easily room for those in the PCB. That would also allow the use of simple 1N400X or 1N540X alternatives for the less fussy folk.
« Last Edit: August 27, 2009, 06:11:48 AM by Kingston »

[silent:arts]

Re: Benefit of schottky rectifiers in linear PSUs ???
« Reply #7 on: August 27, 2009, 06:31:42 AM »
[silent:arts],
If you remove those useless (or even harmful) rectifier caps, there's easily room for those in the PCB. That would also allow the use of simple 1N400X or 1N540X alternatives for the less fussy folk.
mhm, wouldn't give enough space, and I can't reduce the trace width there.
could be possible to add more solderpads for mounting different diodes verticaly instead of the bridge rectifier.
we will see. but the PCB is already near 300 holes, if it gets more it gets more expensive.

more opinions please :) - not only for this PSU, in general.

Moby

Re: Benefit of schottky rectifiers in linear PSUs ???
« Reply #8 on: August 27, 2009, 07:41:50 AM »
I used BYV27/400 (without smoothing caps) and I was pleased with results
For microphone transformers,  BV.8,  Bv.11,  Bv.12, etc.. contact me at mobyelectronics at gmail dot com

sahib

Re: Benefit of schottky rectifiers in linear PSUs ???
« Reply #9 on: August 27, 2009, 08:52:16 AM »

I used  BYV29 on my psu. I did not make any listening test therefore I can not comment on its sonic effects, if it makes any at all.
I used it simply because it is there and I do not have to worry about the cost as it is a diy stuff. Same thing applies to all the other components that I use. However, the views vary on this issue among the well established designers/writers who also do subjective tests. While Douglas Self says it would make no effect on the sonic performance, Morgan Jones highly recommends fast rectifiers for valve amp designs.


burdij

Re: Benefit of schottky rectifiers in linear PSUs ???
« Reply #10 on: August 27, 2009, 09:31:16 AM »
The rectifier diodes in high current areas should be at least fast recovery. This prevents the very narrow spikes of current at zero crossings when both rectifiers are conducting. We used MR851s in the 5 volt and memory drive power supplies in an instrument we built at Tracor Northern.

I am curious why you selected an LM350 instead of an LM338 for your voltage regulator. The LM338 goes up to 5A.

The diodes across the rectifiers themselves are okay but your values are a bit high. More is not better here. These diodes are to suppress line transients from destroying the diodes. You should also have one across each secondary.

You should have a small, low inductance noise suppression cap across each electrolytic. I use .1uf monolythics usually.

I don't think using a positive regulator to build a negative supply, the way you are, is optimal. This will have some detrimental effects on the servo loop. One of the problems with packaged regulators for negative supplies is that they don't have as high a rating as their positive voltage counterparts. You do have enough margin to use a negative regulator and pass transistor, though. There are some circuits in the National datasheets.

I would consider using pre-regulators to bring the +24V supply down to feed to the +16V regulators but that is just because I'm allergic to paying for a power transformer with five secondaries. Also, you could feed the +48v supply from a full wave voltage doubler, eliminating the need for another secondary. The +48 power consumption is going to be less than one amp for an 11 slot chassis even with mike pres in every slot.

Svart

Re: Benefit of schottky rectifiers in linear PSUs ???
« Reply #11 on: August 27, 2009, 04:39:29 PM »
Sorry guys, I didn't notice the thread until now!

Burdij just mentioned the most important thing, the reverse recovery currents.  Schottkys don't have this.  It's this burst of power that emits EMI.

I've used the MUR820 and 860 in some linear designs and they seem to work just fine.  I've tried some others but I don't remember what the model was.  I'll try to find out.
« Last Edit: August 27, 2009, 04:46:53 PM by Svart »
Welcome to the GroupDIY leper colony! when something falls off, we just replace it with a tube!
occupation: General Electron Mayhem

Alesis X2 information repository:
http://www.theopiumdenproductions.

ChrioN

Re: Benefit of schottky rectifiers in linear PSUs ???
« Reply #12 on: August 27, 2009, 04:47:28 PM »
[silent:arts]: I feel for you. This is not easy. Good luck!
"All PCB traces are curved to emulate the electrical response of point-to-point wiring" -Drip

[silent:arts]

Re: Benefit of schottky rectifiers in linear PSUs ???
« Reply #13 on: August 27, 2009, 05:44:28 PM »
[silent:arts]: I feel for you. This is not easy. Good luck!
thanks ;D

it easy for the GDIY51PSU since the prototype is working clean and good.
but if it can be easily improved why not?

this is more an educational topic, and very interesting for future "designs" (I'm far away from being a circuit designer, I follow the data sheets and the knowledge from this forum).

Svart

Re: Benefit of schottky rectifiers in linear PSUs ???
« Reply #14 on: August 27, 2009, 10:31:35 PM »
Another happy side effect of using Schottkys or fast/soft diodes like the HexFreds is that the recovery curve is easier on smoothing caps.  This can generally allow you to use less bulk capacitance or use a lighter duty cap if you wanted to.

Welcome to the GroupDIY leper colony! when something falls off, we just replace it with a tube!
occupation: General Electron Mayhem

Alesis X2 information repository:
http://www.theopiumdenproductions.


 

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