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    solution to over current / protection circuit

    Hello all,

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    I am trying to find a solution to stop my measurement setup from drawing power if the ucontroller losses power, or the computer controlling the setup reboots. Putting aside a lot of the details: I have an arduino based ucontroller controlling a stepper motor control board. The arduino is powered by the computer's USB but the motor control board has its own source (in order to supply enough current). Under normal operation, the motor control board has an enable input, which when pulled high stops motor control board from sourcing current. However, if the enable signal isn't present, the motor control board will draw its full load, 1A in this case. Is there some clever protection circuit i could make to prevent this from happening when windows decides to reboot my compter?

    My first inclination was a series pass transistor between the power supply and motor control board board. the transistor gate would be controlled by the arduino's 5V output. However, if the computer reboots, the arduino board will provide the 5V but no signal to the enable pin, causing current to flow again.

    Thanks in advance,
    Sami

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    Re: solution to over current / protection circuit

    Consider IC "load switch" products, which have the
    pass device (with or without features like short
    circuit protection and inrush control, which you may
    want or not) and the logic interface all together. A
    passive pullup resistor and an open drain output
    that only comes "live" when self-checks and reboot
    have concluded, and there you are.



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  3. #3
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    Re: solution to over current / protection circuit

    Hi,

    Thinking quickly, and about a homespun solution, and you'd need to truth table the details to elicit the desired outcome of 1 or 0..., maybe a NOR to sense either signal or absence of them with perhaps a NOT at one NOR input and maybe another NOT would be needed at the NOR output to control the pass transistor.

    Those are pretty useful combinations for that kind of thing, but again, only offering an idea to work from, not a calculated solution.



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    Re: solution to over current / protection circuit

    Hi,

    If you need more assistance, then consider to draw a wiring overview. Hand drawn is O.K.

    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



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    Re: solution to over current / protection circuit

    Hi again,

    It sounds like a sequence more than a combination, that's clunky in analog, better suited to code, a flipflop would switch at the wrong times and a counter would be cumbersome to use and equally prone to glitchy erroneous results. Anyway, rather than using the Arduino 5V, perhaps the PC USB 5V power signal could be sensed or counted/ff'ed to control the transistor, or combined with any other reliable signal. I understood that normal operation has two states (EN high or EN low), power down one (EN low) and power returned one state that is identical to one of the normal states of operation (EN low). Not fun to contemplate with an analog combinational solution...
    Last edited by d123; 14th February 2020 at 00:16.


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    Re: solution to over current / protection circuit

    Hi,

    A rough idea based on guesswork: NOT gate (or transistor inverter) from PC USB at Arduino V+ into OR gate, other OR input from MCU MCB enable control output pin, OR out into MCB enable.



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    Re: solution to over current / protection circuit

    How about adding an invert gate to the motor board powered by the motor power.
    The inhibit signal is then low, so a power loss from the ucontroller will turn off the motor board (adding a pull-down resistor to the inverter input will help insure that).
    Of course the inhibit logic will need to be inverted from the uC as now inhibit is low, not high.
    Zapper
    Curmudgeon Elektroniker


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    Re: solution to over current / protection circuit

    Hi,

    Due to unforgivably bad phone cover, it has taken well over 1 hour and a walk up and down hills + 20% phone battery to upload sketch of the concept...

    Attachment 157745



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    Re: solution to over current / protection circuit

    Hello all!

    Just wanted to say thank you. You all are right, a little digital logic goes a long way. I inverted the enable signal in software, and used an inverting logic chip powered off the motor's power supply. If the arduino or computer dies, the positive enable signal will always be present to shutdown the motor controller.

    Best,
    Sami



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    Re: solution to over current / protection circuit




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