Hi All

I recently did a remote monitoring system that required battery backup.  I
basically used an 'on-line' system.

It was three basic modules:
1 - battery charger.  I used an adjustable regulator to reduce the 12V DC
input to 6.75 volts to float charge the battery
2 - Battery discharge protection.  Lead acid batteries do not like to be run
flat. I used a TL431 to control a relay that disconnected the battery at 6
volts.
3 - Output regulator.  I used a low dropout regulator to drop the 6 -6.75
volts to 5 volts

The simplified schematic is at
http://www.mumert.com/batterysupply.gif

Dave Mumert

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