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How to replace LT3083 with opamp+pass transistor
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AloyseTech:
Hi!

I have started a small PSU design that would at first be using an LT3083 (or dual 3080). But I would like to make precision high side current monitoring. The shunt has to be placed at the output of the power stage and not at the input like in Dave's µSupply. Since the LT3083 can't compensate high side shunt directly, I thought about using an external op-amp and pass transistor that could include the shunt in the feedback loop. I originally imagined a schematic that could compensate the LT3080 but I looks quite complicated. As a input supply I have a Vout+3V pre-regulator. The target output is 0-15V 0-2A. The shunt value is 1ohm. Spec of the output should be typically similar to the TL308x option.
I'm working on an SMD design which is space constrained and have no active cooling possibilities.
What parts could be recommended for this design?

Thanks for your help guys :)
Zero999:
My advice would be used the LT3081, which includes current monitoring. It's limited to 1.5A, but two in parallel could be used to get 2A.
http://www.analog.com/media/en/technical-documentation/data-sheets/3081fc.pdf

One problem is these ICs have a minimum load requirement, but that's easilly fixed with a constant current load.
AloyseTech:
Thanks, but the Imon output of the LT3081 doesn't meet my requirements. I would liketo be able to monitor current down to the fraction of µA.
Zero999:

--- Quote from: AloyseTech on September 20, 2018, 01:21:12 pm ---Thanks, but the Imon output of the LT3081 doesn't meet my requirements. I would liketo be able to monitor current down to the fraction of µA.
--- End quote ---
Then you'll need different shunts for different ranges. You won't be able to reliably measure the entire range of 2A, with sub-µA precision/accuracy.
Kleinstein:
In a linear regulator there will be quite some power loss, no matter what. One can save a little on the power loss to make it lower heat and thus more compact by using 2 or maybe 3 raw voltages.

The more common lab supply circuit uses an extra auxiliary supply (e.g. extra transformer) for the regulator.
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