LM317-10A-1.2 to 30 V power supply advices

Discussion in 'The Projects Forum' started by jm-a, Apr 10, 2016.

  1. jm-a

    Thread Starter Active Member

    Oct 20, 2010
    105
    2
    Hi all,

    I only " translated " , a power supply schematic for an halogen lamp - 45 W , about 4A under 12V.

    In fact, i plan also to use it for more projects .

    http://electronics-diy.com/electronic_schematic.php?id=981

    It would be great, if someone could check my schematic copy.

    Of course, ( 15 * 1,414) - 2 is only 19,21 V .

    Thanks a lot.

    jm
     
    Last edited: Apr 10, 2016
  2. dannyf

    Well-Known Member

    Sep 13, 2015
    1,824
    364
    It will output a voltage that varies slightly with varying load - in my book, that doesn't work as a regulator.

    It is very easy to check it yourself - read the datasheet.
     
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  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,998
    745
    your better using a Pnp series pass transistor, than npn.
     
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  4. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    As dd told you, better use a PNP transistor as pass transistor.
    This picture from the hamradio magazine " FUNK Amateur march 2016" shows you the effect of using the PNP pass transistor:

    Pass_transistor_on_regulatos.jpeg

    Sorry for the german text, but the images are clear.

    Bertus
     
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  5. eetech00

    Active Member

    Jun 8, 2013
    650
    112
    Hi

    You might consider using a step down (buck) controller with external switch.
     
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  6. Marcus2012

    Member

    Feb 22, 2015
    349
    26
    I've seen that 7805 pass PNP diagram before in the datasheet for the 78xxs and I couldn't figure out why that PNP doesn't have a base resistor. It seemed a bit odd but I figured there was something I didn't understand.
     
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  7. jm-a

    Thread Starter Active Member

    Oct 20, 2010
    105
    2
    Hi,

    As usual, thanks a lot for your replies.

    Great site.

    jm
     
  8. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,292
    1,255
    I'm guessing your worried about the base current? The 317 acts as the base resistor. The circuit has no short circuit protection anymore as it is. You could add a little resistor in the base to current limit the transistor again.
     
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