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Thread: new 8-18V to 12V 6A design : help needed

  1. #1
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    Exclamation new 8-18V to 12V 6A design : help needed

    Hi,

    I am currently trying to design my homemade up to 10A 12V regulated car power supply based on a "miracle" national chip : the LM3478MM
    http://www.national.com/pf//LM/LM3478.html

    I have simulated with their online webench but some composant seems non adequate.
    Could I share this design to someone here willing to help please ?

    I have received 5 sample from this supplier and want to rapidly build a prototype capable of a mere 3A to begin with.

    Thanks in davance

  2. #2
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    I didnt read the datasheet but I cant see that working as a 12V regulator. That chip will pass anything over 12v to its output, and as you know car battery voltage flactuates alot from 8V during cracking upto 14V during charging.

    Apply 14v to its input on the simulation and see what happen to the output.

  3. #3
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    simulated with 8V in


    simulated with 17V in


    This is a switching device and time resolution is 10^-6 sec, that is 5Ás per division.

  4. #4
    Raw Wave Rob Withey's Avatar
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    You need boost/buck topology for output being in the middle of input range. Afaics this regulator is boost topology only.
    Old Systems retired due to new car
    New system at design/prototype stage on BeagleBoard.

  5. #5
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    This chip is SEPIC capable, and this is what I wanna use.

    Am I wrong ?

    Here is the shematic...

  6. #6
    Raw Wave Rob Withey's Avatar
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    sepic is good. you didn't specify that, and the application circuit on the page you linked is not sepic.
    Old Systems retired due to new car
    New system at design/prototype stage on BeagleBoard.

  7. #7
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    Oki, I dunno why it is not, so I've found this other shematic from an application note,



    is that better suited to what I want ?

    tks

  8. #8
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    finally, I wonder if this
    http://www.trcelectronics.com/Meanwell/sd-50a-12.shtml

    would not be a better solution :
    cheap enough and 4.2A out vs 9-18V in but 72% efficiency means some heat to dissipate at high loads...

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