I looked up the DE-SWADJ, and found two versions (1A and 3A max current) of a
step-down voltage regulator. One amp is a bit low for an e-cig, so the 3A version would probably be more suitable.
Step-down converters require that the input voltage be higher than the output voltage, though, so you'd have to use two
batteries in series to power the DE-SWADJ. The datasheet was also not very helpful compared to most that I've seen.
If you want a single battery solution, then you should go with a step-up (boost) regulator like those that
retird pointed out. I've been looking at the
TPS55340 recently, but have not tried it. It would require proper circuit design with several other components.
If you're looking for an assembled PCB solution, there is the DNA12 (or DNA20) and the Nivel Chip that are designed specifically for e-cigs, as well as generic regulator boards from places such as ebay, like ones mentioned in this
thread:
http://www.e-cigarette-forum.com/forum/battery-mods/259577-just-lm2596-users.html
That one is a step-down, requiring two
batteries, and not very efficient. It is pretty simple to use, and quite cheap to buy.
Also, the LEDs in your circuit would likely blow and/or drop your voltage to the coil. You need to limit the voltage and current through them, usually using a
properly calculated resistor, and you do not want them in series with the atomizer. If you have a voltage display, they would likely not be necessary.
Speaking of the voltage display, I suspect that it would need to be connected to the high and low side of the regulator output, not just in series with the high side of the circuit.
I'd suggest reading through as many threads on VV builds in this forum as possible before tackling this.
