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Old 26th October 2003, 09:54 AM   #161
Bricolo is offline Bricolo  France
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I have a question about grounding/return paths.

My next 2 pictures will show the 2 possibilities I'm thinking about, and I don't know which is good.


The 1st uses some kind of "floating ground", the ground of each component (PCB) is taken from the component (PCB) before it.
When I'm thinking about return paths, this one looks better.
But if somewhere in your circuits you have to feed multiple loads, or loads that have other sources connected to it, you'll have ground loops

The 2nd connects every ground to star ground, but return paths create loops :/


Help!
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Old 26th October 2003, 09:56 AM   #162
Bricolo is offline Bricolo  France
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2nd scheme:
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Old 26th October 2003, 11:23 AM   #163
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While being no expert on this, I suppose the answer could
depend on the actual detailed content of those boxes. I
think Jan's discussion of this in part 3 of the TAA articles
will provide you with a satisfactory answer (in theory, at least).
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Old 26th October 2003, 12:31 PM   #164
Bricolo is offline Bricolo  France
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Quote:
Originally posted by Christer
While being no expert on this, I suppose the answer could
depend on the actual detailed content of those boxes. I
think Jan's discussion of this in part 3 of the TAA articles
will provide you with a satisfactory answer (in theory, at least).

Can I find this article on the internet?
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Old 26th October 2003, 01:17 PM   #165
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No, I don't think so, but you can order the full series here: http://www.audioxpress.com/magsdirx/...x/aabilist.htm, 1995 series.

Alternatively, Walt Jung may have an electronic copy.

Jan Didden
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Old 26th October 2003, 02:36 PM   #166
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Quote:
Originally posted by Bricolo
2nd scheme:

Scheme 2 gets my vote. Using a sense ground connection allows the star ground point to be moved from the "regulator" block to the "circuit" block.


JF
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Old 26th October 2003, 02:45 PM   #167
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Precisely. If you take both the 'hot' as well as the return sense lines from the circuit block, you control the supply right at the point where you would want the ideal DC source. That is the concept of the remote sense in the Jung/Didden/Galo regulators.

Jan Didden
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Old 26th October 2003, 04:03 PM   #168
grataku is offline grataku  United States
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Default Re: A picture may not not beat a thousand words

Quote:
Originally posted by Fred Dieckmann
"At this point anyone that can't understand what you said shouldn't be messing with the circuit in the first place."

I was joking about refusing to help anyone. But as you point out, changes of this nature require an intimate knowledge of the circuit. I really don't think most people should make changes this extensive. Despite the description, there are about a half a dozen questions one should be asking before attempting these mods. There is more to this than I have described, and I would not attempt this on the basis of only what I have written, it is insufficient information. I do think I add the LM329 level shifting circuit but it will require a little Spice modeling to do correctly.

As you can see Andy's stock version is much nicer looking than my modified version and is shown with the DIP op amp package option.
I had already privately asked ALW about the substitution of the 10 k with the current sink, and to possibly use a better voltage refference, guess where I got that idea from...
ok ok I'll tell you: it was the CCS for the AlephX you posted years ago,
As I recall ALW seemed to think the led-resistor combo was good enough, but quote me on that.

Decoupling the OPAMP PS looks like a good idea, but what do I know?
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Old 26th October 2003, 06:35 PM   #169
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Lightbulb Just extreme design I guess......

"ALW seemed to think the led-resistor combo was good enough."

With a pre-regulator I absolutely agree.
When you look at an unregulated supply for the regulator it might be a different story. Assuming about 40 ohms for the LED impedance (which is function of bias current), 10K gives about 4 mV per volt of change for every volt of change on the input voltage. With a 100 ohms degeneration this gives a change in current of 40 uA per volt of change on the unregulated supply. This gives an effective output impedance of 25K for the current source, which is very low for a current source. This is MUCH lower than the impedance of the same current source with a well filtered reference voltage for the current source and the bottleneck for the performance of this part of the circuit.

Using a 1.8 mA JFET current source like the J507 will give about 1 Megohm impedance which is a couple orders of magnitude better than a 10K bias resistor for the current source LED voltage reference.

All this points out the obvious question of how good is good enough. Design in this manner doesn't require a lot of math and gives insight to circuit changes to might be impossible to measure in the finished circuit. Methods like these often bridge the gap between subjective and measurement oriented design. This example illustrates something easily measured in the subcircuit, but who's influence might be below the noise floor in power supply rejection measurements at the regulator output.
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Old 26th October 2003, 08:19 PM   #170
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Default Fet CCS

"On the replacement of the LED current source with a JFET current source'

Actually I was taking about replacing the resistor biasing the Green LED reference for the voltage reference for the BJT current source. Replacing the PNP with a ZVP3310 and the zener with two series Green LEDs for the voltage reference would make fet current source with low dropout voltage if one wanted to replace the PNP.
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