About March, 2004 I ordered a kit from eBay IIRC, from a guy in another country, might have been Britain. He called it a Linverter. At that time I didn’t have that much experience with DC to DC converters. I assembled it, made some modifications to it and learned more about how to get the performance required to drive LEDs to full brightness from a 1.5 volt AA cell.
The schematic shows what at first looks like a two transistor “”Joule Thief” type V booster, but it’s not. It’s an astable multivibrator with one collector load resistor replaced by a 33 uH choke. The circuit runs fairly fast – 166 kHz – and does a good job of driving four white LEDs. However I don’t think the 120 ohm resistor needs to be that low. I think it could be increased to 220 ohms or more without much penalty in performance. That would save some battery current. I changed the output transistor to a high current one, but the BC337-40 does a good job of putting out current and it’s much easier to obtain than the one I used. If I needed more current I would just put a second BC337-40 in parallel with the output, but give it its own choke and add the LEDs to it, like the original. This circuit looks similar to the one that CMG patented for their Infinity LED flashlight. I have included the schematic here.