Creating a high voltage current source controlled by microcontroller

[Zero999]

Does the actual current need to be controlled by the MCU or will just on/off action do?

Well On/Off is fine in the worst case, but now that we are going to this much trouble, why not a true VCCS? is there too much difference between having it as On/Off or a true VCCS?

Because there are simpler ways of doing this if it only needs to be on or off?

[sean87]

 Ok i am all ears for only an on/off solution...

[Zero999]

I'd use the TL431. Q1 and Q2 can be replaced with a single TIP121, to reduce complexity.