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Charge Indicator Circuit help

Discussion in 'General Electronics Discussion' started by IMtheS, Feb 16, 2017.

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  1. IMtheS

    IMtheS

    5
    0
    Mar 7, 2015
    Guten Tag!

    I'm planning to do a project, wich contains a 3Cell Li-Ion Battery Pack with a Charge/Balance/Protection board (13.5V Charge Input).
    The main load is controlled by a MCU that needs to know when the battery is beeing charged. The LED will be replaced by an optocoupler, connected to the MCU.

    I came up with this circuit:

    [​IMG]

    Will this work fine? Any suggestions?
    (I'm pretty new tho electronics)

    Cheers IMtS
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    9,548
    1,972
    Nov 17, 2011
    This may work or not, depending o the tolerances of the components. difference between 12.4 V and 13.5 V is not easy to ditinguish with a zener diode only. A more precise circuit would involve a stable reference and a comparator. A TL431 or TLV431 has both in one chip. Chapter 10.2.1 in the datasheet shows a suitable application.
    With a little modification it should work:
    upload_2017-2-16_18-57-30.png
    Use the additional resistor from the REF pin to ground to create a voltaeg divider with Rin such that for 13 V the input voltage is higher than 1.24 V (the internal reference).
    Calculate Rsup such that Iled = (Vsup-1V)/Rsup.
    Vsup is the supply voltage, so it is either 12.4 V or 13.5 V which will give you a bit of tolerance in the LED current, but that shouldn't matter. Or use the 5 V (3.3 V) of the MCU as power supply.
     
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