Don't! Choose a different IC, designed specifically to boost from a single cell LiPO.
700mA @ 12V is 8.4W, which will require more than 2.8A input current at the battery's end of discharge voltage, far more than a MC34063 can handle without an external switching transistor. Although the MC34063A can theoretically work down to 3V, its horribly inefficient at low voltages and wont provide enough gate drive to switch an external MOSFET effectively with under 4V supply. It also doesn't have any protection against over-discharging your battery.
is LM2577 good for me?
Re: is LM2577 good for me?
I have some emergence lights at 12V running on car battery. When used in "mobile" mode, I powered them with 12V from LM2577 (plus 18650 LiIon cell) instead of lugging a car battery around.
Mine is at 700mA normal and super-bright tops at around 1.2A. Having used that for a few years, I would say it sure works but not efficient at all. Physics just gets in the way. I wont go into the detail that "power is proportional to square of the current" and all that. If you are interested in those details, post another reply here and we can dig into those nitty-griddy details.
Here is the net-net. It would be optimistic to target 65% efficiency. Beside the efficiency issue, the high current draw results in high voltage drop. To boost 3.7V to get the same wattage as 12V@1A (Using 1A for easy math here), you would need 12/3.7 Amp = 3.24Amp.
For 700mA, that is 3.24*0.7 =
2.27Amp.
For a single 18650, pushing out 2+ Amps would result in a rather high voltage drop rather quickly. The more the voltage drop, the more amperage it needs which of course worsen the problem more. Sooner than you can imagine, the 18650 drops to the 2.6V cut off. So the two problems in combination, the 3000mAH would have battery life that feels like a 1000mAH. You need to parallel a couple (or more) 18650 just to spread out the current draw to reduce the voltage drop.
I still use those emergency lamps I put together with single 18650+boost. It gives me a better light spread than a single Cree T6+18650 and I prefer that good brightness-spread when cooking or washing up. For other tasks that narrow beam will do, I go with the single T6+1x18650. The boost (
with heat sink) works and works well - but from an efficiency stand point, it is a looser.
EDIT:
I should add this: While I have used those boost for a long time, but time-ON is short. Each use is about 10-15 minutes to do cooking/washing. I don't want to leave the impression that I ran it "stay ON from full charge to full discharge" often. Heat as well as current draw are problems. So very quickly, I switch my my "regular" to "low" to extend the battery life. If you run it 700mA-ON-till-full-discharge, you may find it less acceptable than I do.