logic battery backup

Discussion in 'The Projects Forum' started by magnet18, Jan 19, 2011.

  1. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    Hi there,
    Im working on my nixie clock project and was wanting a battery backup circuit that would power the logic when the wall-wart power was lost, such as in a power outage or if the clock needs moved.
    Im planning on using a 12Vdc power supply and if i can get away with it, a 9 volt battery backup.

    i came across the circuit in this thread http://forum.allaboutcircuits.com/showthread.php?t=3106
    and was wondering if it could be modified to work for my purposes
    i was also wondering if a capacitor would be needed somewhere to prevent the logic from messing up at the moment power is lost, im using 4000 series logic chips and so far ive had plenty of problems with them being sensitive

    Thanks in advance :)
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Possibly.

    However, you still haven't posted schematics of your circuit - so where it would go is completely up to you at this point.

    You'd also just want to power the portion that does the counting - otherwise, you'll drain the battery very quickly. You might do that using a small-signal MOSFET, like a 2N7000.
     
  3. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    124
    Would either of these work?

    edit: is the resistor necessary?
     
    Last edited: Jan 19, 2011
  4. SgtWookie

    Expert

    Jul 17, 2007
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    The first schematic is better, but you don't need the resistor.
    I'd use Schottky diodes, like 1N5817, 1N5818, 1N5819. Less of a voltage drop.

    You don't want to be powering anything more than the ICs that actually keep track of the hours/minutes/seconds, or you'll be wasting a good bit of power.
     
  5. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    124
    Yea, after i posted it i figured the resistor was only necessary for sources of equal voltage

    im assuming that since you said the first one is better that the cap isn't necessary, is there anything that should be done to ensure that the logic isnt interrupted?
    it will be powering a 4060, 4013, and 6 4017's, they will all have a .1uF bypass cap at the power in pin.
     
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