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0-20mA / 0-10V voltage and current source
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rvalente:
Hello mates,

i'm trying to make a 20mA/10V driver (signal output from a device, to drive VFDs and other industrial equipment):

Requirements.

Source topology (active loop), supplied by external 24V
20mA @ 2.5Vin or 10V @ 2.5Vin, user selectable. I wish was only a single jumper bridge.
In voltage mode, current limited, anything from 20 to 100mA is good enough
In current mode, drive up to 600ohms loads (12V output)
Frequency up to 1KHz

The 2.5V input will come from STM32F1 DAC (12bit), using a 3V reference

I wish the opamp will run at 5V (or 3.3V), I would like to some general purpose, low drift, nothing fancy.

First I tought of using a howland current with external transistor but, the opamp output should be higher than 5V to drive an NPN as source

Them I tried to feedback the opamp from a differential current sense resistor (49.9Ohms).

Using ltspice the circuit has a strange behavior (high gain, I suppose) when connected to the opamp, but not with a 2.5V signal source.

I would like to learn more about analog electronics for sure.
Micke:
Here is some inspiration on the current generation part:
http://freecircuitdiagram.com/2010/09/27/op90-4-ma-to-20-ma-current-loop-transmitter/
rvalente:
I appreciate the suggestion, bur the opamp rail is 5v, the maximum voltage i could turn the transitor on would be around 4.4v or 220ohm, i need to go up to 600
rvalente:
Okay, got it to work after some reading...

I wanna use also as voltage source, but with current limiting.

R13 with R14 makes the feedback for voltagem control, replacing the current feedback it works fine, how to tie the two signals?

Voltage subtractor in another opamp?
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