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Low drop out voltage regulator.

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

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  1. beanman


    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.

  2. davenn

    davenn Moderator

    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 :)

  3. beanman


    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. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Try using digikey. Start here. That's 34,000 low drop out regulators to choose from.
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    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. zalmonox


    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

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


    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. Electrobrains


    Jan 2, 2012
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