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Constant voltage source from a battery

Discussion in 'Power Electronics' started by HAL9000, Nov 11, 2012.

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  1. HAL9000

    HAL9000

    4
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    Nov 11, 2012
    Hi all
    I want to obtain a constant voltage source from a battery. The problem is that when the battery discharges the voltage lowers. How can I do?
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    11,513
    2,651
    Nov 17, 2011
    You need a voltage regulator. Without more information (battery voltage, load voltage, load current) we cannot help any further.

    Harald
     
  3. HAL9000

    HAL9000

    4
    0
    Nov 11, 2012
    Thank you for the reply, I already tried to use a LM317 as follows
    [​IMG]


    But when the voltage of the battery lowers, also the output of the LM317 lowers of the same amount:
    [​IMG]
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    11,513
    2,651
    Nov 17, 2011
    What is your input voltage, what is your output voltage?
    Did you observe that a linear regulator like the LM317 needs a minumum difference between input and output voltage for correct operation (voltage drop)?

    Did you use bypasscapacitors as described in the LM317 datasheet?
    And you did use the adjustment resistors aas described in the datasheet, shure you did. Di you?
    And you did not mix up input and output of the LM317?

    I suppose it is one of these points where the error is hidden. Otherwise the LM317 is a fairly well-tempered chip.
    Show us your schematic.

    Harald
     
  5. HAL9000

    HAL9000

    4
    0
    Nov 11, 2012
    Hi, in the previous post I attached the schematic as image. If you can't see it this is the link:
    https://www.circuitlab.com/circuit/3yz7ye/screenshot/540x405/

    I have to check voltage drop and I'll read LM317 schematics, maybe I'm making something wrong, thanks
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    11,513
    2,651
    Nov 17, 2011
    Sorry,
    neither the image in your previous post nor the link you give do work. I get an "Error 403: Forbidden". That is possibly a site that requires login. Please upload the image directly to this forum. Use the "Go Advanced" button below the message window. Click on the paper clip symbol to upload an image. Note the size restrictions.

    Harald
     
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