LM317 Regulator Question

Discussion in 'General Electronics Chat' started by NM2008, Apr 21, 2009.

  1. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    Hi,
    With regard to the LM317 regulator circuit attached below,
    could somebody tell me is it possible to connect another LM317 regulator ic in parallel to the one in this diagram, to achieve a regulator circuit capable of handling 3A, instead of 1.5A.

    Can LM317 regulators be connected directly in parallel to one another in order to handle more current?

    Thanks for your help.
    Regards NM
    7Vdc1.5ARegulatedSupply.PNG
     
  2. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    Hi NM,

    The datasheet for the LM317 shows how to connect three in parallel to boost the current to 4A. Several additional components are necessary in order to keep them regulated and for compensating for output variations.

    It also shows how to do it with one regulator and some bypass elements.

    The datasheet can be found here: http://www.national.com/ds/LM/LM117.pdf
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You could use an LM338 5A positive regulator: http://octopart.com/search?q=LM338
    or an LM350 3A positive regulator: http://octopart.com/search?q=LM350

    You'll need to watch your power dissipation. If you're considering using a circuit like this in an automotive application, the system voltage will be around 14. With a 7v output, the regulator will be dissipating as much power as the load; with a 3A draw, that's 21 Watts. You'll need a big heatsink.
     
  4. yasir9909

    New Member

    May 22, 2008
    3
    0
    Why don't you better try LM2576.It can provide 3A output current.It has fixed 5v output voltage version as well as 3.3V, 5V, 12V, 15V, and adjustable output versions.
    LM2576 Wide input voltage range, 40V up to 60V.

    regards
    m.yasir
     
  5. ruleworld

    Member

    Jun 9, 2006
    22
    1
    it is possible to add more LM317 in parallel.i use 3 of them in parallel to get 4-5 amps. but it is not the recommended way. the best way is to use pass transistor.
     
    PackratKing likes this.
  6. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    Why is the method ruleworld stated not recommended?

    I take it that when
    is mentioned, he means setting up three lm317 regulator circuits, then paralleling their output pins.

    Will the regulator break down after time, by doing it this way?

    Could someone tell me why this is not done.
    Regards NM
     
  7. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,343
    Hello,

    Did you also see this 5A powersupply in the datasheet of the LM317?

    [​IMG]

    Greetings,
    Bertus
     
  8. jvjtech

    Member

    Jan 26, 2008
    23
    0
    Current hogging. In a parallel arrangement, if one regulator starts "hogging" the load current the other regulators may not carry their portion of the load current. The one that is "hogging" more than its share of the load current may overheat with unsatifactory results. The additional components in circuits with parallel series pass transistors, regulators, etc. are intended to balance the currents in the parallel branches. Regards. JJ
     
  9. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
    It is a lot better to use the LM317 as the regulator for higher current series pass components.
     
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