2v7 to 12v5 booster - 70mA

Just one of those circuits one has to design from time to time to provide useful 12V power to a control circuit from a low volt source - here 2v7

R6 and D3 provide the dummy load in this simulation.

R1 sets the peak current in the Darlington pair, Q2, Q1, here 0.6V / 0.5 ohm = 1.2 amp peak

A small-ish iron powder toroid ( or gapped RM6, RM5 for example ) core can be used to make the 47uH inductor - with the feedback winding ( same number of turns ) -> going to Q3 to provide good turn off.

Operation is very simple, R3 turns on Q2, Q1, turn off via Q3 when V across R1 gets to 600mV

At turn off, L1 dot goes high, D2 conducts into Q3, giving enhanced turn off of the Darlington pair.

Q3 stays on until current fully decays in L1, where-upon, the process repeats

here 23.5kHz

pwrtrnx.com

here is the Vout regulated version:

and the mosfet version: