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Power & Energy
Forum LM317 in parallel - Answered -> LM2596 circuit question
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Related

LM317 in parallel - Answered -> LM2596 circuit question

ckambiselis
ckambiselis over 12 years ago

Hello,

 

I am building a DC-DC converter to convert the 14.8v 6A power coming from a professional camera battery to 9V 2.5A used by a DSLR, I am trying to build this converter using the LM317 since it's the only easily available power regulator (which I don't have to order 2500pcs to place an order), the problem is the LM317 can only output 1.5A max, can I build the circuit using 2 of them and connecting the outputs of each circuit in paralel to get 9V 3A, is there going to be any kind of problem that may fry the camera?

 

Thank you

Oscar

 

Message was edited by: Christos Oscar Kambiselis

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Top Replies

  • mconners
    mconners over 12 years ago in reply to johnbeetem +2
    In the LM 317 datasheet http://www.ti.com/lit/ds/symlink/lm317.pdf (sorry about the pdf) figure 13 on page 12 shows three of them in parallel (of course with supporting circuitry) to create an adjustable…
  • Former Member
    Former Member over 12 years ago +2 suggested
    I invented the Lm317. It is NOT designed to be paralleled. If you parallel devices, one will supply all the current until it thermally or current limits and then the other one will come on. This not reliable…
  • mconners
    mconners over 12 years ago +1
    One thing to keep in mind is that you said you will be running this off of a battery. I think John Beetem is correct in asserting that you will be generating quite a bit of heat with this circuit. Heat…
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  • Former Member
    0 Former Member over 12 years ago

    Hello Folks, I have studied regulators and it's my opinion that if you use three identical regulators you could get away with the triple in parallel circuit, but the best bet is figure 14 of the data sheet. You don't have to slavishly follow the designed semiconductors so if one chip or transistor is unavailable try Googling the original part number e g TL080 and you will get access to a data sheet, decide what are the important parameters, in this case its an FET op-amp if I'm not mistaken (look it up) and try to Google for equivalence tables which should be available. The more time you spend in the design stage the better since you will accumulate knowledge and become adept at scanning data sheets. A lot of info on data sheets is superfluous or unnecessarily accurate. Then make up your 1st stab as a breadboard and put it through its paces. You can tell if a device is overheating with your fingers, but I can recommend getting a non-contact thermometer/pyrometer (digital) which are available for under £20. Then you can do some graph plotting. It's a wonderful hobby and also profession, but to be professional you have to surrender the serendipitous side of things and crack your problems. Happy hunting.

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  • Former Member
    0 Former Member over 12 years ago in reply to Former Member

    PS the reference M Conners gave for the data sheet was wrong, change 117 to 317 in the URL.

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  • mconners
    0 mconners over 12 years ago in reply to Former Member

    Interesting, that link was there yesterday. It was the datasheet for the LM117 and the LM317. And yes, now it is the circuit on page 12 , figure 13.

     

    Thanks.

     

    Mike

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  • mconners
    0 mconners over 12 years ago in reply to Former Member

    I updated the link and the reference.

     

    Mike

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  • mconners
    0 mconners over 12 years ago in reply to Former Member

    I updated the link and the reference.

     

    Mike

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