Hi Tulus,
Most of the voltage sources can provide 20mA or more current. You don’t have to use a voltage to current converter for that.
As far as I know the term ‘voltage to current converter’ comes in theory only, in practical cases we call it ‘current amplifier’. It is nothing but an amplifier with voltage gain 1, but it can source lot more current than the actual voltage source is capable of.
All you need is to short the output pin with the inverting input pin of the opamp. The voltage can be given to the non-inverting pin.
Hope this helps.