Sure and yeah w C.V. and limiting current with diodes(small sig, zener, LED, tunnel, yada yada) Vf/Vz junctions, the total Vf of the LED(s) is just "used up" if you will and the left over(excess) voltage then sets the total circuit current,
It = (Vt - Vf)/R
Solve for R @ 300mA and assume Vf...