Small DC UPS?

Discussion in 'General Electronics Chat' started by ill_switch, Mar 31, 2010.

  1. ill_switch

    Thread Starter New Member

    Mar 8, 2010
    Hello all,

    I'm working on a microcontroller project that will normally be running on a "wall wart" power supply plugged into a wall outlet in my home.

    I'd like to build a UPS such that the controller runs on a batter if/when the wall wart fails or loses power. The controller has a 5v regulator onboard and will probably need a few hundred mA, worst case. Runtime requirement isn't really set in stone; an hour (or several hours) would be fine.

    This had led me to consider a small number of NiCd or NiMH cells for the backup battery.

    What I need help with is designing (or finding, I'm sure there's something out there) a circuit that will do the following:

    1) Under normal operation when the wall wart is supplying power, manage the battery (i.e. fast charge if it's down, overcharge prevention, trickling to keep it full, etc) and run the controller on the wall wart.
    2) When the wall wart goes down, switch to battery backup.

    I see ICs out there like this:

    that sort of look like they were intended for this purpose, so I think I may be on to a solution already, but would like some verification from people who have done this sort of thing before.
  2. ill_switch

    Thread Starter New Member

    Mar 8, 2010
    Ok, I picked a chip for each purpose (battery charging and powerpath management) and came up with this:


    I used the LT1512 for the charger and the LTC4412 for the powerpath controller.

    I'm assuming I'd use it with a 5 or 6 cell NiCd or NiMH battery.

    Still I'd appreciate comments from some of you who have done this sort of thing before I go off and build it!

    Active Member

    May 15, 2009
    Buy a small UPS. You can never make it for the price. Be sure that it is a double conversertion type. The batterty size determines the standby time.
  4. Roger at CCCC


    Jun 8, 2009
    This is exactly what I have been wanting to do for a long time but could never figure out an easy way to do it. rvh002, what do you mean by a "small UPS"? The cheapest ones that I have seen are at least $50. and are considerably more powerful than I need. Do you have some UPS suggestions? Thanks !!