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Low drop out voltage regulator.

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Discussion in 'General Electronics Discussion' started by beanman, Aug 17, 2012.

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  1. Aug 17, 2012 #1
    beanman

    beanman

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    May 23, 2012
    I am currently in the R&D stages of a Altoids tin iPhone charger but the voltage regulator I am using is much to inefficient. If anyone could tip me off on a voltage regulator that takes 9v down to 5v and has a drop out voltage of .7v (but a lower dropout voltage would be better) it would be very much apricated.

    -Ben
     
  2. Aug 17, 2012 #2
    davenn

    davenn Moderator

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    Sep 5, 2009
    Hi Ben,

    Have you googled low drop out regulator ?

    there are many to choose from, then look through the data sheets and find one with the lowest dropout voltage :)

    cheers
    Dave
     
  3. Aug 17, 2012 #3
    beanman

    beanman

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    May 23, 2012
    I have but I have been haveing troubble finding one. Maybie I was being to specific in my searches or something.
     
  4. Aug 17, 2012 #4
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Try using digikey. Start here. That's 34,000 low drop out regulators to choose from.
     
  5. Aug 17, 2012 #5
    Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Where's the catch?
    A low drop regulator is one that can operate at a very low drop out voltage, but the voltage that really drops is the difference between input voltage and output voltage.So in order to regulate 5 V from a 9 V battery the regulator needs to drop 4 V.
    Why the need for 0.7V drop out voltage? I guess you want to quench the last drop of juice out of the battery. But a linear regulator (even low drop) is the wrong approach. Depending on the current drawn it will very effectively convert the excess voltage from the battery to heat. In that case a switch mode regulator would be much more efficient.
     
    Last edited: Aug 17, 2012
  6. Aug 19, 2012 #6
    zalmonox

    zalmonox

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    Aug 19, 2012
    Indeed tehre is something about the undestanding of the problem. A low drop-out regulator is a regulator that can potentially use an input voltage very close to the desired output voltage (so close as the low drop-out value).
    Ex. if you want 5V on output and your DC-DC has a drop-out of 0.5 it basically means you SHALL power it with at least 5.5V to work.
    As much for the model (to get 5 from 9) this is another story. Pay attention with the LDOs ... they will dissipate a lot.
    In the case above and for a current of 100mA (not much!) they will dissipate:
    (9-5)*1/10 = 0.4 W which is already a lot.
    You might want to use a switching regulator in this case.
    Look at this on www.Digikey.com
    296-12290-2-ND
    296-18037-2-ND

    Good luck
     
    Last edited by a moderator: Aug 19, 2012
  7. Aug 19, 2012 #7
    gorgon

    gorgon

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    Jun 6, 2011
    You don't say anything about your charging current or the max voltage input range.
    The efficiency you have is also not listed.

    I stipulated the following:
    Vinmax = 12V
    Vinmin = 3V
    Vout =5V
    Ioutmax = 1A

    Just for fun I put this into webench designer from TI/NS and came out with the following SEPIC design:
    The efficiency of the converter is 80-84%

    TOK ;)
     

    Attached Files:

  8. Aug 20, 2012 #8
    Electrobrains

    Electrobrains

    259
    5
    Jan 2, 2012
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