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battery serial/parallel auto switching circuit

funinalaska

Ok, I have a bizarre question.

I have a device that will work at either 4.2v-3.5v or 8.4v-7.0v and it does different things in either configuration.

It draws a fair amount of current in either config.

It was designed to run on 18650 batteries using 2 either in parallel or in series.

Is there a way to make it so that the battery sled will automatically detect and switch between the two modes?

I am thinking 2 or 3 mosfets should be able to do this I just can't figure out how to do it.

Anyone out there have any ideas?

I'd like it to be able to simply supply the correct way depending how the batteries are installed.

 

I guess I should mention that I am trying to keep this small.

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    Dual OP Amp as a voltage comparator (Or even simply use a dual comparator)

     

     

     

    One end of each is connected to a reference voltage (Zener and a couple pf resistors should work there)

     

    The other end is to the battery

     

    The outputs of the op amps will be high or low depending on the voltage of the battery

     

    If you use open collector dual comparator then it gets simpler

     

    BOM would be an 8pin dial comparator, a zener, a handful of resistors

     

    Done.

     

    If you want to do it with a micro-controller let me know, that’s a longer description image

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  • 0

    Dual OP Amp as a voltage comparator (Or even simply use a dual comparator)

     

     

     

    One end of each is connected to a reference voltage (Zener and a couple pf resistors should work there)

     

    The other end is to the battery

     

    The outputs of the op amps will be high or low depending on the voltage of the battery

     

    If you use open collector dual comparator then it gets simpler

     

    BOM would be an 8pin dial comparator, a zener, a handful of resistors

     

    Done.

     

    If you want to do it with a micro-controller let me know, that’s a longer description image

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