3v-9v variable dc from 12 dc

Discussion in 'The Projects Forum' started by 360smokers, Dec 23, 2013.

  1. 360smokers

    Thread Starter New Member

    Dec 2, 2013
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    Hi Sir I would Like to get variable voltage starting from 3 V to 9 VDc, With an input of 12V Dc. With 4 Amp Current limit. If you could provide me with schematics with excellent efficiency It would be really helpful to me. Waiting for your reply
    Deepak Kamble
     
  2. Wendy

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  3. tindel

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    Sep 16, 2012
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  4. bountyhunter

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    Sep 7, 2009
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    317 can't possibly provide 4A.

    I recommend a 5A version of a simple switcher. You can go to TI's website and find there are many to choose from.

    Here is one:

    http://www.ti.com/lit/ds/symlink/lm2677.pdf

    Use the adj version so you can adjust the output voltage.
     
    Last edited: Dec 23, 2013
  5. ronv

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    Nov 12, 2008
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  6. #12

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  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    No, BH, Figure 47 on the datasheet is exactly what the OP was asking for. A very elegant solution to create a switching supply from a LM317.

    Figure 47. 4A Switching Regulator with Overload Protection
     
  8. bountyhunter

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  9. bountyhunter

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    OK. Looks like something the marketing guy dreamed up after a five beer lunch. I would not use it for a variety of reasons, like there are much cheaper and easier ways that wouldn't be so large with so many parts.

    Still can't believe you can buy a 100W DC-DC converter complete for $12 on ebay, but you can.
     
  10. tindel

    Active Member

    Sep 16, 2012
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    After you questioned the circuit I did some spice analysis... the regulation on this thing sucks... I agree with BH's suggestion to use a dedicated switcher... unless someone can see something that I'm missing. There are many chips available on the market... everyone makes several, and you can buy them on fleabay for a few bucks as already discussed.

    I did just suggest it based on simplicity of using a linear regulator... but the circuit is pretty complex. A dedicated buck switcher will work better.

    I am curious if anyone can see a way to improve the regulation of this circuit though... maybe I'll learn something.
     
  11. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    To make it behave better; but still not as good as a modern switcher chip:

    Reduce the series resistance of the input supply V1, or reduce the esr of the input capacitor C1.

    Reduce the Inductor L1 to 60uH, probably means that it is switching too fast.

    Increase the capacitance of C6 to 1uF

    Reduce the esr of C4.
     
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  12. tindel

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    Sep 16, 2012
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    Hmmm... tried all of those things (with the exception for C6 - I didn't have a C6 in my schematic) - the step load response did not improve to usable levels.
     
  13. Brownout

    Well-Known Member

    Jan 10, 2012
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    Try the circuit of figure 39.
     
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