Voltage to Current Converter using Op-Amp
The following circuit converts an input voltage Ve into a defined output current I2. In this example, an LED is operated at nominal current without a series resistor:
Voltage to Current Converter using Op-Amplifier
The input resistances of an OP-Amp are very high as you know. This means that the current I2 in the feedback must be the same value as the input current: I1 = I2
I1 can be determined according to Ohm's law by the input voltage V1 and the input resistance R1:
I1 = V1 / R1.
This means that we actually have an input voltage V1 converted into an output current I2.
Note: As the OP-Amp always tries to keep the voltage difference between its two inputs at zero, the Voltage at the minus input is kept to 0 V in this circuit (keyword "virtual zero point").