Currently I use a LT3083 as a constant current source more or less according to the datasheet as given in the first image. Instead of a single set resistor however is use a fixed resistor in series with a variable resistor connected via a cable to the case of my device which is generally not recommended as I'm told.
In the future I would like to set the current with a DAC if possible like this:
Unfortunately, the datasheet does not offer any more details to this configuration and it only works as a voltage regulator. How would I have to modify the second schematic to create a DAC controlled current source with the LT3082? Is this even possible?
Thanks!
Best Answer
Once again, the 4-resistor difference amp is your friend. The circuit they show you has the output of the LT1991 referenced to ground, but it can also be referenced to Vout, like this:
simulate this circuit – Schematic created using CircuitLab
OA2 acts to keep the voltage difference between OUT and REF equal to the voltage difference between IN+ and IN-. This means that you can now control the voltage across R1 — and therefore the output current — by means of a ground-referenced voltage Vset coming from your DAC.
This circuit shows a gain of 1, which means that Vset must be limited to 0 - 1V, but you could actually use a gain of less than 1, which would allow you to use a wider range of DAC voltages. Just keep R3 = R5 and R4 = R6.
You can get amplifiers with matched resistors built in, such as the LT6363 family. In particular, you might want to use the LT6363-0.5.