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Old 8th February 2013, 02:01 PM   #11
tent is offline tent  Germany
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ok, will do..

but what makes me also think is that I see very same reasonings and implementations (a la CarlosFM) also in other, let's say professional, or not DIY, style PSUs, like for instance this one from TexasInstruments: http://www.ti.com/lit/an/snaa057a/snaa057a.pdf

it is basically exactly same.. 0.1uF snubbers, 0.1uF+1R snubbers, etc.. ok there is an additional 1uF snubber.. but ok.. and no R3/ resistor here as well..

tent:wq

PS: I speak of unregulated PSU of course..
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Last edited by tent; 8th February 2013 at 02:03 PM.
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Old 8th February 2013, 02:59 PM   #12
JMFahey is offline JMFahey  Argentina
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Yes, I see it.
In fact, they state
Quote:
CS7, CS8 act in conjunction with RS1 and RS2 to decouple the large electrolytic capacitors and reduce impedance
which is true as a concept.
Now I'd love to know what's the measurable or audible effect of that.
As in:
What's the impedance difference between a 10000uF cap and a 10000.1uF one?
What's the ripple difference between a 10000uF cap and a 10000.1uF one?
and so on.

Before you tell me "what about high frequencies"?
Well, I already see a .1uF cap in parallel.
What improvement might make adding a 1ohm resistor in series is beyond me.

Mind you, we are talking *this* , line frequency PSU ; in SMPS it's a whole different World.

As a side note, even if that PSU design "comes from TI", it might very well be the pet idea of somebody working there.
I found it strange, to say the least, their specifying the *Brand* of all components, up to specifying "Panasonic 1 ohm resistors". ??????????????

That said, TI themselves add the following statements, which match my concerns and then some:
Quote:
Many of the capacitors used may not be commercially necessary or may have a minimal effect on performance.
Quote:
For a commercial design, bench and listening test or some other test criteria is
recommended to determine the exact number, size, and type of external components required.
But this is the final "sledgehammer in the head" disclaimers:
Quote:
The values for the different capacitors were not chosen based on extensive bench work or research.
Quote:
The equations and methods to determine optimal
values are beyond the scope of this application note.
Really?
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