A member here approached me about making a low output, long runtime boost driver to fit the Convoy T2 (aka Manta Ray S1, also available as a host at Kaidomain). Target output was ~1 lumen. No mode switching. Currently 17mm but could be made to be 15mm or about any size.
I went through a couple iterations and ended up creating one that ran an XM-L2 at 2.5mA for ~0.7 lumen for 98 hours on a 900 mAh AAA Eneloop Pro. So on a AA battery, it should run for 12+ days. It runs down to ~0.7 V.
Current is set with a single resistor. Current output could easily be set higher or lower as desired.
Oshpark link. BOM:
- TLV61220 Boost IC
- Inductor, 1210 footprint (I used a 10uH but 4.7uH should work as well; look for lower DC resistances)
- 2x 0603 or 0805 capacitors with 10 uF (pretty much any 10uF cap should be fine)
- 1x 0603 or 0805 current set resistor (resistance = 0.5V / desired amps, so for 3mA: 0.5 / 0.003 = 167 Ohms)
- Spring and wires