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Current Regulator

Discussion in 'General Electronics Discussion' started by Omran65, Apr 10, 2017.

  1. Omran65

    Omran65

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    Apr 10, 2017
    hi
    I have a question :
    I want to make current regulator
    LM317 can't work because the voltage of my circuit have be same in output and input
    Vi 14v
    Vo 14v
    Io 0.1A
    can you help me?
     
  2. davenn

    davenn Moderator

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  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Current regulators require something to sense the current. Most methods of doing this will incur some voltage drop, even if it is only 0.1V.
     
  4. Omran65

    Omran65

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    Apr 10, 2017
    you guess when my output current is 0.1A my voltage is be lower than 13v?
     
  5. Omran65

    Omran65

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    Apr 10, 2017
    I have output voltage of my circuit is be higher than 12.5v anyhow
    can you proposal simple circuit to me?
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Take a look in the LED resource. There is a simple constant current source that can drop less than 1V. For lower drops you need more exotic circuits.
     
  7. Alec_t

    Alec_t

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    By 'current regulator' do you mean a controllable constant-current source or a current-limiter?
     
  8. Omran65

    Omran65

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    Apr 10, 2017
    l have to use this circuit for very slow charging solid battery
     
  9. Alec_t

    Alec_t

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    What battery chemistry? Lithium batteries are very fussy about their charging regime. A dedicated battery charge control IC might be better/safer than just a constant-current source.
     
  10. BobK

    BobK

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    Your question, as stated is asking for something impossible. You cannot have a current regulator that has an output of 14V and 0.1A. To regulate current, the voltage must vary depending on the load. Perhaps you really mean that the output voltage must be capable of going all the way up to the the supply voltage if necessary. This is called the compliance voltage.

    As others have said, you cannot even measure the current without some loss of voltage.

    If what you want is 14V in and and current regulator all the way up to 14V, you will probably need to boost the voltage first, then run it through a current regulator.

    Bob
     
    Omran65 likes this.
  11. Omran65

    Omran65

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    Apr 10, 2017
  12. Alec_t

    Alec_t

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    The link doesn't work.
     
  13. Omran65

    Omran65

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    Apr 10, 2017
     

    Attached Files:

  14. Bluejets

    Bluejets

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    I've used a standard plug pack (transformer type, not switchmode) 12v 500ma supply via an adjustable LM317 current regulator for different applications for years.

    The supply outputs more than 12v with varying loads naturally, but just trying it now on a fully charged (via another auto charger yesterday)12v sealed lead acid 7Ah battery, it will still deliver 40mA at maximum adjustment on the pot.

    So I think your 1.3Ah battery should be ok with something along these lines.
     
  15. Omran65

    Omran65

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    Apr 10, 2017
    This circuit should be OK?
     

    Attached Files:

  16. duke37

    duke37

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    You have shown a voltage regulator, I thought you needed a current regulator.
     
  17. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    This will limit the current:

    upload_2017-4-11_18-40-11.png

    Assuming the regulator variable with a nominal 1.25V output:

    Vout at 0A is 1.25 * (R1 + R2)/R2
    Iout (short circuit) is 1.25/R3

    There is a linear relationship between these points.

    If you're planning to charge a 12V lead acid battery, I'd set Vout as 14V and Iout as maybe 1A
     
    Omran65 likes this.
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