can you fix XL4015 Step-Down CC/VC low voltage problem

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  • harp
    Badcaps Veteran
    • Jun 2022
    • 570
    • Planet Earth

    #1

    can you fix XL4015 Step-Down CC/VC low voltage problem

    I notice some issue with handy XL4015 Step-Down DC Module with CV/CC Control, so I ask if that can be fix or lower/minimise effect...

    Its about that module cant hold CC when voltage is set less than 1.7v
    If you have that module, please confirm that.

    Here is visualisation table for fixed 100mA CC, measuring output in short :

    set 3.0v - 100mA/0.00v in short
    set 2.0v - 100mA/0.00v in short
    set 1.8v - 100mA/0.00v in short
    set 1.7v - 100mA/0.00v in short
    set 1.6v - 300mA/0.00v in short
    set 1.5v - 900mA/0.00v in short
    set 1.4v - 1.8A/0.45v in short

    In schematic pin #2 is going to voltage set trimpot, and near TL431 trimpot is for set current.

    I'll be glad if I can modified it for more reliable use, but dont know how, it will be awesome if it can work with low voltage and correctly hold current.
    Attached Files
  • stj
    Great Sage 齊天大聖
    • Dec 2009
    • 30927
    • Albion

    #2
    Re: can you fix XL4015 Step-Down CC/VC low voltage problem

    just a thought,
    i'm probably a bit wrong but it looks like the overcurrent from the comparater goes through an led.
    maybe the led voltdrop is the issue at what ii frankly well below the voltage drop of an led!

    Comment

    • eccerr0r
      Solder Sloth
      • Nov 2012
      • 8664
      • USA

      #3
      Re: can you fix XL4015 Step-Down CC/VC low voltage problem

      There's a limit to what you can do with a circuit that "simple" ... probably running it at its limits when running it that low of a voltage.

      Oh and yes agreed you probably get a little better (but not perfect) behavior if it didn't use an LED there.
      Last edited by eccerr0r; 03-02-2023, 01:07 PM.

      Comment

      • harp
        Badcaps Veteran
        • Jun 2022
        • 570
        • Planet Earth

        #4
        Re: can you fix XL4015 Step-Down CC/VC low voltage problem

        I place jumper over led, and it is better, but not very reliable.
        The voltage fluctate about 0.2v, maybe depend on heating some component...
        With jumper over led and 100mA set, I can lower voltage to 1.40v, and get 107mA measured on short. But, if I lower a just one bit over, say 1.37v it "limit" randomly arround 300-700mA. On 1.5v it seems work ok...

        Ok, the fact is that with jumper is enhanced version
        I will replace led with 000 resistor.
        Thank you!

        Comment

        • sam_sam_sam
          Badcaps Legend
          • Jul 2011
          • 6019
          • USA

          #5
          Re: can you fix XL4015 Step-Down CC/VC low voltage problem

          By the way this is a charging board and yes you can go down to almost 0 volts at different current rates I had one do this and it not suppose to work that way

          I did have one module that the current adjustment did not work correctly and I got weird results like that sometimes it go to 0 volts shorted and sometimes it would not I just stripped it for parts

          The only difference between the modules that have the meter module and ones that do not is the pot controls on the meter modules ones have the pot adjusters are on the side and ones pot adjusters are pointing up which makes it impossible to adjust the pot controls unless you remove the meter module and you can not mount the the meter module

          The higher the voltage/current ratio will depend what your voltage will be try another module and see if work correctly or not you do not have to get it with the meter module

          Here is the same buck converter that uses the red circuit board the black circuit board is also interchangeable as well

          https://www.ebay.com/itm/13260658909...Bk9SR7TZo83UYQ
          Last edited by sam_sam_sam; 03-02-2023, 06:20 PM.

          Comment

          • eccerr0r
            Solder Sloth
            • Nov 2012
            • 8664
            • USA

            #6
            Re: can you fix XL4015 Step-Down CC/VC low voltage problem

            err... a diode still needs to be there, simply shorting the LED out will cause problems - replace with a regular diode, hence it would only be a little better. Even a red LED probably better than a green one there if that's what it was.

            oh...btw... shorting it out will be the best you can do with what you have, anyway. however you should note you cv mode is broken with the LED shorted out.
            Last edited by eccerr0r; 03-02-2023, 07:04 PM.

            Comment

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