Battery Low

Discussion in 'General Electronics Chat' started by dogstail, Aug 5, 2008.

  1. dogstail

    Thread Starter Member

    May 8, 2008
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    I am looking for any idea's / circuits on a battery low indicator the battery will only be 3v need the indicator to activate at 2.5v. Can any one help thanks.
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Do you need it to light an LED or just give a voltage level? A simple op am with a couple of resistors and diodes would do the latter just fine.
     
  3. dogstail

    Thread Starter Member

    May 8, 2008
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    Just looking to light up an LED
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    OK, it gets a bit tricky, but is doable. The problem is the voltage needed to light up the LED. Older LEDs use less dropping voltage, so I'll assume that. Someone else may come up with something better, but I'll see what I can draw up in a bit.

    **************

    OK, I've never built this, but I think it should work. I was aiming for as low power as possible.

    [​IMG]
     
    Last edited: Aug 5, 2008
  5. AchMED

    Active Member

    Aug 5, 2008
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  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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  7. Wendy

    Moderator

    Mar 24, 2008
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    Can either one of those drive an LED?
     
  8. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    The MAX8211 should, if his battery cutoff is 2.5v. Its sink current is 4mA (min) and output saturation is 0.17v (typical...I was wrong earlier...0.4v Max)...that leaves at least 2.1v for a high brightness red LED and current limiting resistor.

    Ken
     
  9. AchMED

    Active Member

    Aug 5, 2008
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    It can swing to Vol+0.4 Vcc worst case. They spec 0.8mA for a 3V rail. More then enough to drive a LED. I usually only use 20 to 30 uA.

    Ive never tested it down to that low a voltage though but according to the datasheet it is doable.
     
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