Transistor CCS resistor value calculation.

[Craig]

Excellent articles by Walt Jung on current regulators

http://waltjung.org/PDFs/Sources_101_P1.pdf
http://waltjung.org/PDFs/Sources_101_P2.pdf

Note particularly the one in part 2 with an LM317 voltage regulator and a heatsunk MOSFET that goes up to 450V