# Electronic – Help with trying to understand Voltage controlled current sources

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I have been looking for weeks for an article or anything that could explain to me how a voltage controlled current source works. I want to know if it's possible to create a VCCS that changes according to a function. What I mean by this is if you can make it so that if the voltage changes according to a function the current changes how you want it to. Can anyone explain to me how a VCCS works and how to make it work according to a function?

One possible way to do it:

simulate this circuit – Schematic created using CircuitLab

$$I(R_2)=\frac{U_1}{R_1}$$

This works because the current into the + and - inputs of the OP-AMP is zero (by definition) and the voltage between them is also zero (by definition). As the OP-AMP is used as a buffer (- input directly connected to output), the voltage at R1 is U1, so the current through R1 is

$$I(R_1)=\frac{U_1}{R_1}$$

and because there's no way out for that current (by definition), that's also the current through R2. Regardless of the value of R2.