I'm a little stumped trying to design a current-based power supply for some power LEDs. Essentially I want them to ramp up from 0mA current to 350mA inverse logarithmically - like a graph of current through an inductor after a switch has been closed. I want the time constant to be approximately one second. All this needs to feed power from 120Vac, 60Hz main power grid. So, I'll likely have a bridge rectifier with a capacitor in series with a resistor, possibly with another cap in parallel with that branch. That can provide me with a nice, smooth ramping voltage across the capacitor. Now I say to myself, how in the world do I translate that into a current? The obvious solution is a resistor, but I really, really want to avoid dissipating heat through a resistor when the circuit is fully on. Any suggestions?