I thought of using 2 LM1084 regulators (up to 5A for a maximum of 3A
load). I would prefer a linear power supply, because I think it is
cheaper, but don't know how to connect the back-up battery, in order to
be able to charge it when powered from the wall outlet.
If it is connected after the 12V regulator, with a diode, how could I
obtain 5V when the system is running on battery ? The 5V regulator
should be located in the schematic after the 12V one and the battery
connection point. But in this case, the 12V regulator should be up to 6A
(3A + 3A), isn't it ?
I don't know if I made myself clear, because my english is not so good,
but I hope someone of you will understand what I tried to explain. I
think this is am usual problem to deal when using dual voltage back-up
power supplies.

Lucian

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Russell McMahon
Sent: 22 martie 2004 13:50
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [EE]: 12V and 5V Power Supply

> I'm looking for a schematic for a dual 12V @ 3A, 5V @ 3A power supply
> with battery backup and charging circuit (eventually). I have searched
> the web and have found nothing similar (only for sale, but I need to
> build it myself).

Google for data sheets and application notes for an LM350 regulator.
This can be adjusted to 5v and 12v at 3A (one for each circuit) .

Basic information and datasheets here

        http://www.national.com/pf/LM/LM350.html

        There are a number of application circuits in this datasheet
that
directly
        address your requirement.


The LM317 is the 1 amp equivalent - there are more application notes
around
for the 317 than the 350.

Datasheet         http://aes.sdsu.edu/documents/LM317-D.pdf



Then come back and ask more questions :-)


        Russell McMahon

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