-48V with buck-boost converter, common ground

Discussion in 'General Electronics Chat' started by manubm, Feb 25, 2016.

  1. manubm

    Thread Starter New Member

    Feb 25, 2016
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    I have a doubt about if I use a buck-boost converter with a -48v input to +12V ouput. Where is my common ground? I need to ground it!
    common_gnd.png
    Thank you
     
  2. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    1) It depends on what is inside the converter. If the output is isolated, you can just connect whatever wire you want as "common".
    2) You could think in terms of an inverting supply. Do you really need both boost and buck to get 12 volts out of -48 volts?
     
  3. manubm

    Thread Starter New Member

    Feb 25, 2016
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    Do you mean that with this configuration i cant use a common earth between input and output?
     
  4. manubm

    Thread Starter New Member

    Feb 25, 2016
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    Sorry the output is not isolated.
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    What is the part number for the converter?
     
  6. manubm

    Thread Starter New Member

    Feb 25, 2016
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    LM2576
     
  7. #12

    Expert

    Nov 30, 2010
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    You did not show a, "configuration". You just drew a square and called it a buck/boost converter.
    Now that you have said what is in the square, I think you have chosen the wrong chip.
     
  8. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    The circuit in post #1 has 60 V max potential difference, -48 to +12. This is beyond the ratings for the standard 2675, and exactly equal to the max rating for the 2576HV, a dangerous thing to design in. What output current do you need? You might be better off buying a small fully isolated DC/DC converter that will do what you want.

    ak
     
  9. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Note, This chip is a Down Converter not a booster, with common 0V ground.
     
  10. manubm

    Thread Starter New Member

    Feb 25, 2016
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    My question is about the common Earth input-ouput.

    I use the LM2576 to convert -48 to +12v (1A max in the ouput).

    How I can Ground the ouput side?

    Thanks.
     
  11. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    There is a circuit trick for doing part of what you want with a buck converter, but it will not work with this chip. And even if it did, you cannot ground the output side.

    ak
     
  12. manubm

    Thread Starter New Member

    Feb 25, 2016
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    Any suggestion chip (60v) to do that?
     
  13. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Post #7 - no.
    Post #8 - no.
    Post #11 - no.

    ak
     
  14. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Manubm, you clearly are not reading these replies, your regulator is a Drop Down Positive converter, you need to use an isolated output type, or negative regulator.
     
  15. manubm

    Thread Starter New Member

    Feb 25, 2016
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    I got it! I will try with a LM5160 Fly-Buck isolated output.

    Thanks
     
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