After some time of using darkstar underground I came into conclusion the maximal light output is far from enough, especially when visiting big cave domes, etc. There's not many ways to increase output power on the board as the LED heat transfer through vias is far from perfect. The solution could be using cooper as base material for PCB, but that's an expensive solution. Also the driver efficiency is not very good, lots of energy is wasted on switching transistor and current measuring resistors.

These were the reasons why I decided to make a new, improved version. The basic operating principle stays the same (hystersis driven buck convertor), but that's all. New version will be powered by attiny (and finally programmed in C, not assembly) and will be designed for 2 A / LED current. Together with thee new CREE XP-L2 LEDS, the light output should be at bat-roasting level :)

Work in progress...