I want to build something like this. This circuit controls 0-20mA but the circuit have one big problem. If the circuit load e.g 100 Ohm changes to e.g 200 Ohm, then less current is going to flow. To solve that issue, I need to tune in the feedback for the operational amplifier by turning on the potentiometern
So I have an idea! What if I measure the current flow over a small resistor e.g 25 Ohm. I then send the voltage difference back as a feedback signal. If I get +3.3v as the reference value, then I should have 20mA as current flow in the circuit.
Like this. But even if I tune in current flow to 20mA when I have +3.3v as reference, the current flow in the circuit WILL change if I change the circuit load.
How should I build up this feedback circuit so when I have +3.3V as reference input signal, then 20mA will flow through the 25 ohm resistor, no matter what arbitrary load we have?