Modify SW5V boost to 12V

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This topic contains 1 reply, has 2 voices, and was last updated by  Shannon Hicks 1 month ago.

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  • #2366


    Dear admin,

    I am working on reading the In-situ LevelTroll 400 water level sensor through Mosbus, it required a 12V-24V input.
    I have check the Mayfly sw5V boost SC4503 datasheet, it allow step up voltage up to 27V.
    If I follow the output voltage formula in the datasheet R1 = R2 (Vout/1.25V – 1), If Vout = 12V, R1/R2 = 8.6
    I need to modify the mayfly on board resistor R19 from 10k to 3.3k which give me output voltage around 12.65V.

    I want to confirm is it okay to do it without modify other components in the sw5V boost circuit??

    Your help is much appreciated

    Best regards

    btw, below is my successful 3G datalogger design using Mayfly 🙂

  • #2370

    Shannon Hicks

    What version of the Mayfly board do you have? The newer boards have a different regulator than earlier versions, so make sure you’re looking at the right datasheet and resistors.

    If you’re comfortable removing and reinstalling SMT resistors, then it is possible to remove that resistor and replace it with another one to achieve different output voltages. But you have to be careful with supplying 12v to external devices so that you don’t exceed the maximum safe current and that the return data is at a safe voltage, otherwise you’ll damage the Mayfly. It’s likely you might need some external level shifters on the return data lines, which is why I didn’t include 9v and 12v excitation options on the Mayfly to begin with. Things can quickly go bad if users aren’t careful about voltage levels, so I decided to keep higher voltage stuff off the Mayfly. You can add an external boost regulator for just a few dollars each (5, 9 or 12v) from here:

    Then you can put that boost regulator on a Grove protoshield ( along with a level-shift breakout and then a header or screw terminal, and then you’ll have everything you need for safely powering an external device with a different voltage.

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