Comments on National Semiconductor Power Supply Design??

[Ron AKA]

I'm interested in any comments you may have on the design of this power supply. They seem to have thrown everything but the kitchen sink at it, especially in the way of capacitors. Your thoughts on which capacitors are of value (aside from the obvious big filter caps), and which may be fluff?

Audio Amplifier Power Supply Design - Troy Huebner/John DeCelles

My interest is in upgrading an older amp with the hope of reducing noise some, and improving channel separation. Will replace the main caps, but after that wondering what else is of value...

[DF96]

A quick look suggests to me that they don't really understand power supplies, beyond elementary textbook level. On the other hand, they seem to have followed every possible audio fad. They don't talk about the need for mains-related capacitors for C1-C4, and I'm not sure all these are needed anyway. They don't appear to have given much thought to proper grounding. The PCB design appears to assume that a thick trace can be regarded as zero ohms - not true when charging pulses are around! Other capacitors seem to appear on the basis that caps must be added between every pair of circuit nodes (well, almost!).

I am surprised. NS application notes used to be much better than this. Maybe this is the new generation of engineers?

[noSmoking]

hi Ron,
Found your post while searching the same thing,I have found a cap .1uf across the primary,a inrush current limiter inline 10ohm, fuse,secondary with a .1 cap,to a bridge with .1 film across each diode ,10000uf cap .1 cap 100uf to a reg in,out the reg to a .1 cap and found 3 different caps here 220uf,or100uf,or 47uf, also it is suggested to bypass at each opamp and major digital chips 10 to 47 uf at the opamp and .1 and 10 uf at the digitals,I also read a .33 across the + and _ on the opamps help the sonics,Now this is just what I have found PLEASE add to it or any Ideas are welcome,I haven't tried this ALL out yet. I have put the .33uf on some opamps and noticed better sound on the op amps(bass and mids improved), seems to be some talk about the kinds of caps too Solid polymers (Nicholson web site) show more ripple rejection,so should this be our .1 cap to use?
I have a bunch of elna's and cerafines and there ez to get so I use them for the middle values and rubycons for the big electrolytic s, I have 10 tantalum in bypass places, can the polymers replace those?I have had that type of cap short(tant) and burn in just a few years old, from what I have found on transformers the E type seems to be most use and recommended,the torrid are smaller and maybe more efficient but also more nosier than the E types I am not a GURU I just read DIY audio alot,Happy hunting!
Cheers!

[noSmoking]

Hi Ron,
Alot of this info is from Nelson Pass thread, his power supplies don't change much so He's on point with what is needed or working like it should, He has a ZERO return rate over 10 years in this business,I'd say he knows!
Regards,

[!]

All caps used are legit for noise filtering, the purpose of some if not all is listed in the app note. You could say that with each added the return becomes less and less but so it goes with capacitors. They generally design for components easy to source (substitutions will be ok, no exotic or especially high performance parts per their kind/type are used).

If your particular transformer, bridge rectifier, incoming mains AC power, wiring, etc does not have or introduce as much noise as someone else's does, you may achieve similar or better results without all the capacitors. Which you omit depends on which portions of your power supply have less noise introduced.

It's an arbitrary amount of components, you could add more and different types of filtering or remove some of what is there, making it increase or decrease in complexity, size and cost. Then consider the amp, this PSU is proposed for powering some of their amp chips but your amp may not meet or might exceed noise rejection of those chips.

[DF96]

If they were really worried about noise they would have used a proper mains filter (which would include the correct capacitor type) rather than a single cap across the mains supply. Some of their bypass caps might actually inject noise into the ground connection. They admit that their component values were not carefully chosen but they simply copied everyone else. No, IMHO this PSU was intended to push audiophile buttons rather than be an example of good design.

[!]

^ It's a better design than most people on DIYaudio are using (or perhaps I should write, "more complete" since we can view the PSU as modular so some will think you only have two modules being PSU or Amp while others will just consider these the only two PCBs present along with other external circuitry) with the exception of higher impedance from use of only a single 20,000uF bulk cap per rail, so I don't see your point.

It isn't valid in the discussion that caring about noise means using a line rated capacitor - less safe perhaps, but no less effective filtering noise. I do not see this design as dependent on specific component part #s, line rated caps can be chosen as well as other parts' substituted as designed. While a full blown mains filter would do better, I also consider the possibility that since these can be purchased as modules and often include a handy IEC socket with chassis mounting ears for a chassis power cord connection, that it isn't necessarily considered part of the power supply itself.

Pushing audiophile buttons would almost certainly include use of audio grade capacitors, certain models of soft recovery diodes.

We might say it's a "generic" PSU example, in that it leverages component types common world wide so in countries where access to parts isn't so good it might provide good performance : price ratio.

Of course if you feel another design is better for that parameter, please do share a schematic...

[noSmoking]

Hi !,
do you know a good mains filter that's buildable a schematic maybe.
Thanks

[abraxalito]

Originally Posted by DF96

I am surprised. NS application notes used to be much better than this. Maybe this is the new generation of engineers?

They shipped out Bob Pease. Its not only the app notes which have taken a dive, the datasheets equally have been going downhill. Be interesting to see if acquisition by TI continues the slide.

<edit>

do you know a good mains filter that's buildable a schematic maybe.

I have a schematic on my blog

[noSmoking]

Hi abraxalito,
I'll try that and see,I also went to the felix project and looked around some good ideas there too!
Thanks,