Maybe it's a MicrOne ME2108A - a switching regulator.
PDFs may be available only with chinese (or the like) text...
Tilmann
P.S. Google for SOT89 2108A to get some results...
Thanks Tilmann. Found a useful datasheet:
http://img.ozdisan.com/ETicaret_Dosy...70_1622138.pdf
The example for the 2108A in the datasheet duplicates the one in my circuit.
Cheers.