simple way 48vdc to 40vdc

Discussion in 'The Projects Forum' started by manuel09, Oct 12, 2009.

  1. manuel09

    Thread Starter Member

    Aug 29, 2009
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    Hello
    Please help if i want a simple way for dropping voltage from 48 to 40V or 48 to 12vdc .
    I need to share by one power supply for several usage.
    48-40v means at 40v to 12v i will use LM317, because hard to find ic regulator with input 48Vdc.


    Thanks
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    How much current do you need at 12V?
     
  3. t06afre

    AAC Fanatic!

    May 11, 2009
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    I think you have to use "switcher" for this project. But this depends much on your current requirements. If it a low current application you may use a linear regulator. But you will still need a quite large heat sink.
    Also a tip. The LM317HV can be used up to 57 volt.
     
  4. manuel09

    Thread Starter Member

    Aug 29, 2009
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    0
    Thanks for all reply, my main power 48Vdc 3A
    but I need this share 12vdc for very low current no more than 200mA.
    any other ic type except LM317HV?, i m not sure can find this type easy.

    thank you
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    An other regulator is the TL783.

    But when you drop 48 to 12 volts at 200 mA,
    you will have to dissipate 36 * 0.2 = 7.2 Watts.

    You will need some heatsink for it.

    Greetings,
    Bertus
     
  6. manuel09

    Thread Starter Member

    Aug 29, 2009
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    Thank you Bertus.
    Let me find first.
     
  7. t06afre

    AAC Fanatic!

    May 11, 2009
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    You could also try the LM2592HVT-ADJ-ND This is a simple switcher. So your need for heat sink will be much less (or not needed at all). The LM2592 series can handle up to 60 volt. Both this circuit and the LM317HV is aivailibel at http://www.digikey.com/
    Then order the LM2592HVT-ADJ-ND be sure it is the ADJ type, not the one with fixed voltage
     
    Last edited: Oct 12, 2009
  8. SgtWookie

    Expert

    Jul 17, 2007
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    The LM317 can handle a differential voltage up to 40 between input and output.

    However, as Bertus said, it will dissipate 7.2W with a 200mA load. A 12v 200mA load is 2.4W. Do you really want to waste 3x the power used in the load in a regulator?

    A switching regulator is the way to go.
     
  9. manuel09

    Thread Starter Member

    Aug 29, 2009
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    Yes seemed its not efficient..how if I use diodes 6A05 * XX in series?
    Just tried 5x dropped 1.64V
    Sorry poor knowledge, pls advise
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    Diodes would still dissipate power as heat, and the regulation would not be very good.
    The forward voltage of diodes changes with current.
     
  11. t06afre

    AAC Fanatic!

    May 11, 2009
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    Yes that is correct, but lm317HV can be used up to 60 volt input and 1.2V to 57V output range. But this is an "old" and expensive circuit. Use the TL783 if you must use a linear regulator. But once more I would recommend a switcher;) Look how few components that are needed in this data sheet figure 1 page 8
    http://cache.national.com/ds/LM/LM2592HV.pdf
     
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