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Voltage divider with voltage follower (power supply)
ConnerP
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02-09-2020 04:44 AM
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Greetings,
I would like to measure the drive signal which controls a piezoelectric positioner using a USB-6343 DAQ. This signal has a range of +-250V and of course the DAQ is limited to +-10V. I know a simple voltage divider can do the re-scaling for me, and from reading I see that a voltage follower is highly recommended to ensure that the DAQ sees a low impedance. Precision is important here, so I do see the voltage follower as necessary.
Where am stuck at the moment is how to supply power to the op-amp for this small application. I've looked for small switch mode power supplies (like the kind they put in LED light bulbs) which I could wire in series to make a virtual ground, but I'm coming up surprisingly empty handed. Could someone more experienced on the board point me in the right direction here?
Also, while I am asking, are there any particular gotchas I should be looking out for in this application?
Thanks!
Buechsenschuetz
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02-12-2020 08:19 AM
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There are many sources for DC/DC converters with symmetrical outputs, such as +/- 12VDC etc. They are available with several input options, including 5VDC. This comes from an european supplier, but I am sure there are many more https://www.tracopower.com/products/browse-by-category/detail/dc-dc-converters/reinforced-insulation...
02-12-2020 08:32 AM
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Hi, I was actually more concerned about converting from AC, since this divider will be an isolated unit. I'm not sure if I did not think about it or what, but I since went back and looked around again. I found some nice small transformers that I could simply use for a linear supply and pass through a LDO regulator https://www.mouser.de/ProductDetail/TE-Connectivity-PB/4900-9020RB61?qs=sGAEpiMZZMvwUzoUXIIvybxvWcHl....
Once I get around to it I will post back with a planned schematic with some specific numbers for the community to look over.
paw510
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05-07-2020 12:42 PM
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What is the point of having an "isolated" supply for the divider/opamp if the signal ground can't be disconnected from the USB ground anyway ?
From the 6343 manual :
"All ground references—AI GND, AO GND, and D GND—are connected on the device. Though AI GND, AO GND, and D GND are connected on the device, they are connected by small traces to reduce crosstalk between subsystems. Each ground has a slight difference in potential."
