I need to build a 36V variable current source, if possible using a single op-amp and a mosfet. I need to control current between around 10uA - 0.5mA ie very low current. This is for some iontophoresis research I'm doing.
The design I envisage is attached. The zener should give a ref voltage of 2.5V and R2 should give variable current based on I=2.5R. That's my theory anyway. Anyone able to recommend R values, Mosfet, IC choices? My power source must be 36V.
The circuit feeds into an H-bridge to generate different waveforms from the output of this circuit.