@c4757p, it doesn't need to be all that accurate, but I would like to minimize the amount of energy loss. (See below for more info.)
@TerminalJack505, no, no other rail available.
My little project is to see if I can power a tiny weather station data logger with a supercap or two instead of batteries overnight. In order to prevent the supercap from losing too much energy too quickly, I want to clamp the current to a max of 100 mA. I'm using a booster to increase the volts to the active circuit, but what I've found is that even though the supercap has the ability to continue to supply the current required, the NSI45035 (which is in front of the booster) caused the current to sag when the input voltage dropped. (Putting the current limiter after the booster didn't help.) Since every joule of energy is precious, I'm trying to minimize power losses, which means trying not to use resistors that just end up wasting energy in the form of heat loss. I'm also trying to keep the circuit's power usage as small as possible, so I'd rather not start adding op amps and such if there's a more efficient way to do this.