This is a 3 NMOS version of:
http://everycircuit.com/circuit/5760014432075776
Each NMOS (N-channel MOSFET) require it's own sense resistor and op-amp diver, so is possible to use slightly different parts.
Each MOSFET sink 1A per 1V set. Therefore, an additional op-amp with a gain of 3 (not included in this circuit) would be useful to monitor the set voltage on a panel meter.
