you can use the USB Self powered topology (Use D+, D- and Ground, don't use the USB ports +5V to your system)
Really? That I would never had thought would be sufficient to charge batteries. I'm not saying that I think you are wrong but I question the constancy of such a supply. I will try it out though since it would be very much easier than using a converter.
I tried to paint up the scenario as best I can and since most components are not jet determined I can't be sure about the current need. But I can with a good probability say that the circuits will need >=100mA but not more than 200mA but that is a calculation done excluding any current draw by the DUT.
How much current can be needed for a versatile LCR meter do you think? I mean regarding the excitation signal and resulting current?
I will replay to all other raised points very soon, by the way if I would change my batteries so as to function as one(3,7V * 2) or change them for one 7,4V battery I have found a ready made reference design from LT using LT8471, it has a reference design designated DC1854A:
http://cds.linear.com/docs/en/demo-board-manual/DC1854AF.PDF
here is LT8471's datasheet if anyone is interested:
http://cds.linear.com/docs/en/datasheet/8471fd.pdf
DC1854 does show a design using one LT8471 + 18 components if I didn't misread it to create a converter that accepts 6-32V on its input and delivers +5V@1,5A and -5V@550mA, that should do it, but I am still looking to see if there are any simpler designs available.
I will have quite a hard time developing the software for this so I am willing to cheapskate my way through the hardware design, I mean a fully functional and independent DC-DC module could be an option if the price allows for it.
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One example could be LT3471....But search other manufacturers, too.
The LT3471 circuit look a lot smaller than LT8471, I will continue searching though and I did not think that there would be so many IC's for this purpose but there seem to exist in abundance.
About that SMPS used 10mm from a 16-bit ADC, what kind of inductor was in use?
I'm not after a very detailed answer to this but I am often concerned with the magnetic field radiating out from inductors in SMPS and I have jet to build a magnetic probe to find out, I have for some time intended to start a new thread about hall-effect sensors since they are the best option for me to build a magnetic sensor though there are confusingly many different kinds of such circuits.
When you say "synchronize the SMPS to overtones of your measurement frequency" do you mean that if I am running a measurement at 10kHz then the converter would be set to perhaps 20kHz or any other harmonic frequency of the measurement frequency?
The only thing that feels strange about such a arrangement is the fact that I intend to use this device to characterize Impedance over frequency over a range of 100Hz to 1MHz and could it not cause problems for the converters if they would have to respond to those wide frequency sweeps?
Obviously they would not be made to follow further down than 10-20kHz if they/it can even get that low as most dc-dc converters seems to be set to >=100kHz.
Regards