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Recommend a good cheap LDO 5V

Discussion in 'Electronic Basics' started by Hammy, Feb 2, 2008.

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  1. Hammy

    Hammy Guest

    Can anyone recommend a good cheap LDO (2 Bucks or less small quantity
    10 or 20), preferably one that doesn't need a $5 tant cap on the
    output? I've been looking through the datasheets at Newark and
    Digikey until my eyes are bleeding.

    The specs are

    Vin is a 9V alkaline initially, then the battery gets switched out and
    a regulated 12V from a flyback takes over. The LDO output should be 5V
    and be able to provide 80 to 100mA continuous.

    I was thinking of just using a L78L05 but I want to be able to use the
    battery until it's depleted. I know I'm cheap.

  2. Chris

    Chris Guest

    Hi, Hammy. The 78L05 has a dropout voltage of 7.0V max, which should
    do fine. There's not much power left in a 9V battery when it gets
    down to 7.0V. But the problem will be when you switch over to the 12V
    supply. You'll be dissipating 0.7 watts at 100mA, which will mean the
    78L05 will get far too hot. (12V - 5V) * 0.1A = 0.7W

    Now, if you go with an LM341/LM78M05C, your dropout voltage will be
    7.2V at 0.5A, and should be comparable to the 78L05 at 100mA output
    current. It's about $0.40 in single quantities from Mouser, and is
    forgiving on the output cap issue -- an 0.1uF ceramic should be fine.

  3. Hammy

    Hammy Guest

    Thanks I wasnt sure when a 9V battery dies. I'll try your suggestion.
  4. John Larkin

    John Larkin Guest

    LM1117 is a cheap "mdo" regulator with a little lower dropout than a
    317. It's happy with a 22 uF aluminum elec on its output.

    Once the battery is down to 6 volts or so, it's dying fast, so using
    that last volt won't buy much more time.

  5. Maxim/Dallas MAX603 came to mind immediately because I'd just been
    playing with one. It might not be able to compete with the (undoubtedly
    good) options others have already mentioned, especially in price, but I
    thought I'd throw it in.

    PDIP/SOIC, modern protection circuitry, shutdown mode, samples, good
    information imo etc.
  6. Steven Swift

    Steven Swift Guest

    If cheap and easy is what you want, try the MIC29xx series from Micrel.
    They have a bunch of different styles and you can get them from Digi-Key.
    Might be a bit more than you want to pay, depending upon package, but
    they'll do the job.

  7. doug

    doug Guest

    Hi , you might want to check out the TS2950ct-5.0 ultra low dropout
    5volt pos. regulator,from Taiwan Semiconductor. 150ma.,only needs 1uf,
    quiescent current only 80microamps,and works right down to 5.2volts input!
    regards all doug.(in U.K.)
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