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It's always handy to have a few constant-current injection circuits in one's bag of tricks, so here are just a few that should be at least considered when the occasion calls for one:
The junction FET circuit was a little troublesome at first. It wanted to oscillate. That's why the 0.01 µF is there to quiet it down. The response time was a little slow, but for the application at hand, that didn't matter.
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(Hi John, I've pasted this over at EDN too)
Has anyone looked at the AD8130 to use as a current source/ howland improvement?
It is basically an opamp with the usual + and - inputs, and an additional feedback set of + and - inputs.
A simple adaptation of figure 139 in the datasheet , where Voffset becomes your load voltage, and Rg sources current into the load. (Rf could be zero). Seems to me this would make the perfect current source.
Iout = Rg x Vin
that's it, one chip, one resistor!
Posted by: Bob Turner | August 14, 2016 at 12:10 AM