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Old 31st October 2007, 09:42 PM   #41
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Quote:
Originally posted by aparatusonitus
your R12 should be parallel resistance of R2 + R6.
Wouldn't that result in an inapproriate high R12 or low R2/R6 string that would eat all current? It would need to be as low as 6R and 16,5R?
Rüdiger
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Old 31st October 2007, 10:05 PM   #42
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I think you mean the input resistor to Q4. The impedance is already matched.
What is the advantage of your Central CS, it has comparativly huge parts count, where other people seem to get by with LM317 wired as CS?
Rüdiger
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Old 1st November 2007, 07:23 AM   #43
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Next time I'll do the math with my fingers instead using my head, you are right, your error amplifier input impedances are good.

Why use discrete master current source instead LM317? Becouse constant-current characteristic of LM317 tends to become deteriorated in the high frequency range much more against discrete CCS, but you could use one LM317 as floating preregulator Walt Young superegulator style as it will clean some garbage from mains.
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Old 1st November 2007, 09:28 AM   #44
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by aparatusonitus
.........Why use discrete master current source instead LM317? Becouse constant-current characteristic of LM317 tends to become deteriorated in the high frequency range much more against discrete CCS,.........
Hi,
the fast shunt regulator hides the slowness of the 317 current source.
I think the 317's only disadvantage in the fast shunt context is high voltage drop. That's why I asked for low voltage drop alternatives and why I was so interested in the voltage drop that On's CCS achieves.
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Old 1st November 2007, 10:55 AM   #45
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Hi,
in sim, using zenys CSS gives an 30dB improvment of high frequency ripple rejection above 100kHz (the graph is acutally more complicated).

With aparatus' CSS I had no improvement, but, since no part values are given, I could have chosen wrong values.

One has to adjust R12 to get the same current, though.
Rüdiger
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Old 1st November 2007, 11:01 AM   #46
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Uh-oh.
Things are more complicated. The sims tells a tendency of oscillation. And you screw up the high F's regulation with that LED at the output of the CS.
Don't know what's going on.
Rüdiger

EDIT: it's mostly wrong what I#ve written regarding those different CSS. The sim results are supersided by the ESR your provide for the caps...
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Old 1st November 2007, 06:13 PM   #47
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I checked the real circuit again at the workbench. It seems, if I use no current source, or current mirror for the diff-pair (j4 in the schematic) I got lower noise. With an active mirror or -source, I can see some noise on the scope at the output of the reg (5mV/div).

And what are your concerns against LEDs? There was a hot debate some years ago here about the noise of leds which led to no consensus (well, not that I know a single issue or thread where consensus had been found...)

Rüdiger
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Old 1st November 2007, 08:57 PM   #48
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Quote:
Originally posted by Onvinyl
With aparatus' CSS I had no improvement, but, since no part values are given, I could have chosen wrong values.
I don't know your load current request, but if you going to try Masao Noro CCS, start with something like 10R for current defining resistor and 681R for the other. For Qs use something like 2SA872/2SA970 and MJE1503x/D4xH11.
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Old 1st November 2007, 09:14 PM   #49
Zen Mod is offline Zen Mod  Serbia
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Noro's patent has all values for parts .

good for analysis

patent 4366432

useful link:

http://www.pat2pdf.org/
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Old 2nd November 2007, 12:45 AM   #50
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Thanks Zen Mod, that gives me a few ideas. I don't see, though, were my main CSS has major flaws. I'll try fet/resistor reference in order to achieve lower noise.

By the way, the use of the cfp in the diff-amp lowers Zout by a factor of 20.

@Andrew: with 100mA, the real reg could have a voltage drop of only 1 Volt. I don't think it's optimum in regard of regulation, though
Rüdiger
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