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JSR03 active parts choices

Started by raq, January 06, 2009, 06:01:58 PM

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Hi all,
Hi Per-Anders,

I'm about to become, hopefully, part of your group, guys, if you welcome me and... help me with some answers.

I'm trying to find a better way of supplying my DDDAC1543 USB board as the built in 7806 does not satisfy me with neither the voltage it outputs (this is for an actual modification of its design), nor with its noise, nor with its bandwidth.

This component needs (1) 7.1V and (2) 3.3V regulated supplies, for each of the stages (DAC, clock, USB receiver) - at least that's how I want to implement it.

I am thinking of either - initially - use a JSR03 for the 7.1V which is the bigger upgrade / urgency (and leave the two 3.3V alone), or get four kits and use three of them for the voltages above.

To cut this short, the most important aspect for me is the output noise of the PS. Therefore:
- what would be the best combination of opamp / voltage reference known to man (...). I've seen opamps down to 0.85nV noise out and voltage references down to 1.3uV (for series). I understood Per-Anders used AD825 plus LM431 to get 5uV out of noise - but the spec sheet claims it can be lower than 1uV with select parts - which parts? Which of the noise values of the parts used is 'overwhelming' in terms of what to expect the PS to output? I'm guessing the voltage reference, as it generally is a few magnitudes higher than the opamp's. At the same time, I'm assuming it's much more complicated than just taking the higher value and calling it the noise value of the whole regulator.
- the voltage reference is series, shunt? Either? I cannot access the download section and cannot read the schematic online;
- do the transistors need to be low noise? selected as such?
Thank you for all of your input. Thank you Per-Anders for your help this far and further.
Best regards,



Download is a pay area. If you read the instructions you'll know how to get the access.

Answer: Don't know yet since I haven't tested every possible combination of parts and besides that new parts are developed all the time. AD825 and OPA134 is two used and tested opamps. More types may fit.

LM329 is nice when it comes to noise but it's not suited for lower output voltages in this design.

The opamp is a major influence of the noise and the transistors minor.

Both the LM431 and LM329 is shunt references but a real voltage reference can be used but then you'll have to patch it in.
/Per-Anders Sjöström, owner of this forum

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