Rather than approaching the specification by successive piecewise
approximation, why not spell out what is REALLY required?

Explaining what you really as clearly and fully as possible is a great help.
It doesn't matter if your English isn't perfect. Just do the best you can to
describe your requirement.

What is the use that the outputs are being put to?
What are the actually required voltages (eg MUST it be 12 or could it be
anywhere from eg 10 to 14)
What are the load levels on each supply? (average, peak, minimum, other
characteristics?)

Is this in a vehicle?
What is the power source (main?, car alternator, ??? ...)
What battery is it that you are talking about charging for backup?
What must be backed up? (12v?, 5v?, both?, how long?
Is the backup battery voltage fixed?
How fast do you want it to recharge in?
Have you got a battery in mind to use or can it potentially be any battery?
Is this a one off, small volume, large volume?

Is there anything else that is going to have to be explained before a full
solution can be arrived at?



        Russell McMahon


> The problem is that getting a regulated 12V out of a 12V battery is a
> relatively "hard" thing, requiring a switching topology of some sort
> (and IIRC, switchers are easier when the output voltage ISN'T that
> close to the input voltage.)  If you could get by with 10V, you could
> use two simple linear regulators (depending on other circumstances, of
> course.)
>
> Are you allowed to use, say, 14V worth of battery?  Or is the 12V
> requirement loose enough that you can get by with an unregulated 12V
> direct from the battery, when the main power is off?

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads