What Type of Circuit is This?

Thread Starter


Joined Dec 19, 2008
Hi all; sorry for being so vague but I'm not sure where to begin.

I have a embedded computer that I want to use an internal battery. I need the computer to run off the battery unless it is plugged into an external power source, then I need it to charge the battery to capacity and power itself off the external source. When I unplug the power source, I should use the battery without shutting down. IE: smooth source transition both directions. I already have the appropriate hardware to handle different voltage inputs, so no regulation is needed - just the transition and charging.

This seems really obvious but I'm not sure where to begin. It seems that part of the circuit is a charge controller but that's only a piece of it. Tons of portable devices do this but I can't find the appropriate name to know where to search. Ideally it would support lipo batteries, but I'd be happy with SLA if necessary.

Thanks much!



Joined Nov 30, 2010
The changeover is dead simple. Just connect the load as if it always runs off the battery and connect the charger to the battery as if there is no load. Making the charger is the hard part because modern batteries are getting really picky about how they get charged.

If you use a SLA, you just make a constant voltage float charger with low current capability. LiPo's and NiMh batteries require a lot more brains about the charging circuit.

How's that for a start?