I need to make a small unregulated step-up that would boost +2.7V from a depleted battery pack to approximately 7V to run an LCD, which consumes micro-amps. Is it possible to do this with a current that comes from the microcontroller pin (with PWM), some passives and a diode. I guess that could be possible, if the output of the microcontroller were open drain.
I’m not a power supply specialist; I’m just playing with this an idea. EDIT: this is more of an exploratory question rather then a search for a solution for a particular problem.
Please let me know if what I'm describing is unclear.
Try LM2577 step up regulator.
It can accept a wide input voltage of 3.5Vdc to 40Vdc,
stepping up your voltage higher to output of 5V, 12V, adjustable.
The choice of output dpend on the IC model number.
The performance will drop if input voltage is lower, for example your case of 2.7V.
**broken link removed**
You can try other IC, using the keyword DC-DC step up regulator.