** Put a 3 amp diode ( 1N5404 ) in series with a AA NiMN cell.
Probably work fine, depending what your big secret device is.
.... Phil
I see it all the time, but I'm still amazed by the number of questions
that show up here without the slightest hint of specification required
to attempt a well-reasoned suggestion.
This elicits the firestorm of suggestions followed by the
inevitable name-calling fest. Are we having fun yet?
My answer to your question is, "Can't be done."
But that's according to MY definition of "small" and MY
assumptions about run time.
Perhaps, you could be influenced to disclose YOUR definitions
of "small" and your desired run time.
Did you really mean 0.5V -2A? and does that mean it's a current sink?
or???
What accuracy/stability is required?
Reasonableness of the answer is highly dependent on the specificity
of the question.
Your question ain't got none.
** That 0.5 volts might just be AC too.
Makes the solution a bit more complicated...............
Shame how so many OPs post entirely in meaningless generalisations.
Means that is how they are thinking too.
..... Phil
For starters, are you saying the wall-wart reduced 120V AC down to
0.5V with a current of 2 amperes, DC?
Well, you DID say 'any thoughts'.
Seriously, do you have any accuracy requirements? AC or DC?
Any preference on battery type (palletload of lead/acid, or
single hearing aid cell)? Duty cycle? Battery life under load?