Smiling Shark SS-5039 1 x AAA size flashlight, modification notes, Now 3 x 7135 with modes, on a BLF Tiny 10 board.

[WarHawk-AVG]

@Fritz t. Cat

Apparently the three terminal thing is a PNP NPN (p channel?) junction field effect transistor or an old fashioned junction transistor. The resistor is connected from + in to the gate or base. The emitter or whatever is also connected to + in. The collector or whatever (plate) goes to + out. - goes straight through to -. To first approximation, the output current is proportional to the current in the resistor, so it should act electrically like a resistor. I get from battery charge state and tail cap current:
2.66 V 0.22 A 12.0 Ohms
3.14 V 0.28 A 11.2 Ohms
3.21 V 0.31 A 11.5 Ohms
So it starts regulating somewhere around 3 V. The apparent slight increase in effective resistance between the last two might be explained by the drop in voltage of Advanced Lithiums under load.
The obvious mod seems to be a lower value resistor and Lithium primary cells, if the transistor can take it. Or if one wants long run time, it is good as is.
0.22 A at 2.66 V is close to the chart for an XM-L2, so the led has a nice low forward voltage.

Per Microa

Experimenting with the Joule Thief circuit

Out of boredom I got interested into the Joule Thief circuit. Yesterday I built two of them using a 2N3904 transistor, 1k resistor, 10mm warm white LED and two different handwound coils. One of the coils is a larger toroid with 10 turns on it, the other one is a smaller one with six turns. So far both of them work just fine. The current draw from an eneloop cell is 40 mA with the larger and 44 mA with the smaller coil. I will make a third one tomorrow with an even smaller toroid with only fou…

Yeah that tiny IC is a solid state version of the joule thief

AX5505-VFM synchronous Step-up DC/DC converter

I think that green resistor is actually a linear choke…a coil 100uH

here is a slightly larger but more powerful VFM voltage booster!
up too 200mA (drive a XR-E or XP-G at lower end power)
http://www.ricoh.com/LSI/product_power/dc_up/rp400x/index1.html