7805 for 4-20mA current injector
The 7805 is a generic part, variants are made by lots of manufacturers, you should check the datasheet for the exact part and make you have used. Typically they recommend a 0.1uF capacitor between Out and GND and a 0.33uF capacitor between In and GND. These are required for stability. In practice, you will probably find that any values greater than these will work fine.