circuit for converting in 0-5v to 4-20mA current source
You can always just use your reference circuit (1-5V input) and convert your 0-5V input to 1-5V with two resistors:



simulate this circuit &ndash; Schematic created using CircuitLab
If you don't have a +5V rail, you can create an equivalent from any higher rail with a pair of resistors and a little math:



simulate this circuit