Electronics > Projects, Designs, and Technical Stuff
Range swichable constant current source
erikj:
You could try something like this:
Turn on one of the mosfets M1-M3 for the range you want. This way the ESR of the mosfets will not affect the measurement.
I added C1 for stability, it might not be needed.
The idea comes from here:
Zero999:
erikj,
That's a good idea for eliminating the MOSFET resistance from the measurement!
R3 and R4 can be two 180R and two 18R in parallel, to get 90R and 9R respectively.
OM222O,
I still think you should consider a proper ADC as well as or instead of the digital potentiometer, simply because it's only 8-bit, which not good. If you have more bits, then you'll probably find you don't need so many ranges.
By the way you'll need to activate the current source for long enough for it to settle, before taking a sample. You'll fine it will take a few ms for the current to settle to the set value.
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