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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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  • 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…
Parents
  • johnbeetem
    0 johnbeetem over 12 years ago

    While I'm not a power supply expert, my understanding is that hooking up the outputs of two linear reguators in parallel is usually a bad idea.  It's very hard to get them to share the load equally, i.e., each put out approximately the same output current.  Usually one dominates, producing most or all of the output current while the other is idle.  I've heard that it's also possible to go into oscillation, with the two regulators fighting each other.

     

    Using linear regulators to convert 14.8V to 9V is a 5.8V drop at 2.5A.  This is 14.5 watts that's going to waste and could make things pretty warm.  You probably want to use a switching regulator, which wastes far less power and runs much cooler.

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  • mconners
    0 mconners over 12 years ago in reply to johnbeetem

    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 4A regulator. You would probably have to order 2500 of one of the other parts in the diagram. image

     

    The regulator they diagram is 4.5 to 25 volts.

     

    Again, though, I defer to the experts.

     

     

    Mike

     

    Message was edited by: Michael Conners

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  • danteo
    0 danteo over 12 years ago in reply to mconners

    Hi Michael,

     

    The pdf is moved here:http://www.ti.com/lit/gpn/lm317  via http://www.ti.com/product/lm317

    I think you talk about page 12 / fig. 13.

    It seems ok.

     

    Hi Christos,

     

    I would use the Webench Designer and choose some switching IC. You can request free samples from TI to try the design.

    I used many LM317 and LM317K (TO-3 case) but they generate some heat at high current as I remember.

     

    Regards,

    Dan

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  • ckambiselis
    0 ckambiselis over 12 years ago in reply to danteo

    Danteo I have used Webench to easily find a schematic for my specs but, as I said, many components can't be found or must be order in 500+ quantities, don't know if it is possible to order samples from TI since I don't work in a big company (I only have a sole proprietorship business) and I'm located in Finalnd, but I will check.

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  • ckambiselis
    0 ckambiselis over 12 years ago in reply to danteo

    Danteo I have used Webench to easily find a schematic for my specs but, as I said, many components can't be found or must be order in 500+ quantities, don't know if it is possible to order samples from TI since I don't work in a big company (I only have a sole proprietorship business) and I'm located in Finalnd, but I will check.

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