Why not Schottkys ?

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OK I am being thick. The silicon diode will drop say 1V x 5A = 5W of heat. The Schottky will drop say 0.7V x 5A = 3.5W of heat, a saving of 1.5W. Plus I will see a slightly higher rectified voltage at the filter capacitors.

Maybe the leakage current? I have looked at the datasheet and unless you heat them up to 125C or subject them to high PIV with respect to their ratings, the leakages are quite small. For example the MBR10100 would leak about 3uA at 25C and at 50V PIV, which is surely negligible?

Something tells me I am missing something.
 
Actually, I used the MUR820 model. I did not have any 6A diodes in "Tina"(TI).
Anyways... One purpose of the CRC filter is to get rid of possible noise from the mains. What is your opinion on the added diode in this context?
Firstly, I think that you can answer a lot of that question by deleting the resistor in your simulation and see that the filtering continues.

Secondly, It might be fun to spot all 6 crc-like filters in that schematic (hint, some of the capacitors are on the amplifier boards, not shown, and some of the filters aren't using resistors as series element).

And, thirdly, if the crc bypass diode is on, we may assume that the system is probably attempting loud replay, in which case stiff rails are important for quality.

Basically, a power amplifier covers a wide range of current and just one crc resistor value is not perfect in all conditions; however, a crc bypass diode can give you additional options.

P.S.
If my supply were simplified, I'd rather remove the filter from the input of the reservoir/tank capacitance and keep the series elements at the output of the reservoir/tank capacitance.
 
But the lower forward voltage drop alone will have a beneficial effect? For example I am using 4 1N5402 in a bridge configuration to rectify 25VAC. When I draw say 5A DC they heat up so much that they have melted nearby components (5mm away). Now I know the 5402 is only rated at 3A without some cooling, but still, is it not true if I had used the SB3100 instead I would experience less heat?

I don't see any obvious benefit from using Schottky's in this application just to save a couple of watts or a slight improvement in voltage headroom for the regulator. Schottkys are also more prone to thermal runaway and conventional Schottkys have a limited PIV and could be blown by a large line transient. You shouldn't ever allow components to run so hot, just on general principle of reliability. Just use larger parts and heatsink as necessary.

A tuned RC snubber across the transformer secondary will reduce ringing/RFI no matter what type of diode is installed.

Whatever benefits a Schottky rectifier brings to >most< designs are marginal and most benefits low voltage/high current switching supplies.

Mind you, I did use Schottky rectifiers when I modified my Hafler SE100 preamp to use the Jung Superregulator. But only because I thought they might induce less RFI; I found the RC snubber was still necessary and had to to 'tune' the values using an oscilloscope (a RF spectrum analyzer would have been preferable) to observe the reduction in ringing. The exact snubber component values will depend on the specifics of the components used in a given design.
 
But the lower forward voltage drop alone will have a beneficial effect? For example I am using 4 1N5402 in a bridge configuration to rectify 25VAC. When I draw say 5A DC they heat up so much that they have melted nearby components (5mm away). Now I know the 5402 is only rated at 3A without some cooling, but still, is it not true if I had used the SB3100 instead I would experience less heat?

25vac, about a 23 watt amplifier. How does it draw 5A?
Is it a stereo amplifier or a bridge amplifier or driving 4 ohm speakers?

Something tells me I am missing something
This is more easily demonstrated with an LED, because at beyond half current capacity, you don't get a lot more light but you do get a lot more heat. Anyway, we could expect the 3A power diode to have a lot of trouble at 5A.

See the diode forward voltage drop vs current graph in the datasheet. Diodes have a sweet spot for current and once that has been exceeded, they get extremely hot and are at risk of breaking. Sometimes a change in the graph curve indicates that point (of when more power is not healthy at all), such as the 1n540X graph.

So, standard silicon, fast silicon and schottky, if a 3A part, would all get extraneously hot at 5A. A 16A schottky could indeed run cooler, if indicated by its datasheet. The larger physical size would also help. The KBPC2504 standard silicon bridge rectifier is also physically large and could dissipate heat gracefully.

P.S.
A bridge rectifier's only means to work, involves a very huge noise, because if it were silent, there wouldn't be any voltage. Therefore, all of schottky, fast silicon or standard silicon, if used for bridge rectifier, could also make use of RC snubbers across the transformer secondaries.

P.P.S.
Power supply rail thickness might need checked and braced up considerably--the heat really should have dissipated a little better.
 
Hmm, the Fairchild diode that Mouser-USA sells for USD 1.60, are on the Farnell UK website for GBP 1.09. (link). At today's exchange rate that's 14% higher, although I'm the first to admit I have no idea how V.A.T. affects the comparison. And, what do I know, perhaps Farnell UK also tacks on hidden fees, after-the-fact fees, government fees, and imported-goods fees, even on items that have "624 in UK stock for next day delivery", like these Fairchild diodes.

The Farnell UK website is what you see plus 20% VAT added at the checkout. No other taxes or charges, if the order exceeds 20 UKP you get free shipping, typically next day.
 
25vac, about a 23 watt amplifier. How does it draw 5A?
Is it a stereo amplifier or a bridge amplifier or driving 4 ohm speakers?
/QUOTE]

It is not an amp, but a 30V/5A PSU.

I do not understand why I used the 1N5402, it is only 3A, completely underspecced. I have redrawn the schematic now using the MBR10100. It is larger with much lower C/W it should be perfect.
 
A tuned RC snubber across the transformer secondary will reduce ringing/RFI no matter what type of diode is installed.. . . Mind you, I did use Schottky rectifiers when I modified my Hafler SE100 preamp to use the Jung Superregulator. But only because I thought they might induce less RFI; I found the RC snubber was still necessary and had to to 'tune' the values using an oscilloscope (a RF spectrum analyzer would have been preferable) to observe the reduction in ringing. The exact snubber component values will depend on the specifics of the components used in a given design.
That's normal.

Some opinion:
Snubbing the AC side is because of the transformer, and that snubbing works fine with any sorts of diodes for bridge rectifier. . . and needed because of using a transformer with a bridge rectifier.
However, snubbing the DC side is because of the diode and if that is a soft switch diode which already has a poor attempt (better than no snubber but inferior to doing a good job with the snubber), in that case, the patchwork job with the shunt RC is far more difficult, therefore I'd much rather use series filters for the DC side whenever the bridge rectifier is made of soft switch diodes.

I was comparing high voltage schottky for power supplies against the KBPC3502 standard bridge rectifier. Of course the standard silicon has a little more voltage drop. That isn't nearly as important as the forward voltage drop versus current, graph pattern, which for the high voltage schottky is like a sag inspiring upslope but for the KPBC3502 standard silicon is more like a straight up wall that is far more attractive for audio power amp, so on that parameter (is regulation the term?) the win goes to. . . KBPC3502.
 
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... the forward voltage drop versus current, graph pattern, which for the high voltage schottky is like a sag inspiring upslope but for the KPBC3502 standard silicon is more like a straight up wall that is far more attractive for audio power amp, so on that parameter (is regulation the term?)
Semiconductor people call it "series resistance". If you've got an exponential diode in series with an (unwanted, but very real) 0.02 ohm resistor, when the current thru the series combo is 2 amps, the resistor "robs" the diode of 40 millivolts of forward voltage. The exponential I-V curve starts to bend over, eventually becoming linear rather than exponential.

Here's a representative SPICE model, created by Diodes Inc and supplied to its customers. Notice the parameter "RS", the diode's series resistance.
*SRC=MURS160;DI_MURS160;Diodes;Si; 600V 1.00A 50.0ns Diodes Inc. Super Fast Rectifier
.MODEL DI_MURS160 D ( IS=17.1n RS=20.6m BV=600 IBV=2.00u
+ CJO=45.0p M=0.333 N=1.73 TT=72.0n )
Series resistance arises from the bulk resistivity of the doped silicon in the anode and cathode; the contact resistance of the metal-to-silicon welds; and the wire resistance of the anode and cathode leads. You can reduce series resistance by using a larger "bar" of silicon to build the diode, and by mounting it in a larger package with less series resistance (like this one)
 
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