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What should I do with unused outputs?

Discussion in 'General Electronics Discussion' started by Braeden Hamson, Dec 16, 2018.

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  1. Braeden Hamson

    Braeden Hamson

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    Feb 18, 2016
    First off, damn this new website looks nice!

    I really feel like I should know this answer but just to be safe. I'm going to use a 74HC163 without any other counters.

    http://www.ti.com/lit/ds/symlink/sn74hc163.pdf ←Datasheet

    Therefore I don't need the "carry out" pin. I know that you should always ground unused inputs but should I be grounding outputs?
    I know it wont short out if I ground this pin because of the internal resistors within the gates of the CO.

    Thanks!
     
  2. Audioguru

    Audioguru

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    Sep 24, 2016
    If you ground an output then it is shorted to ground. Then there will be damage when it tries to go high. The outputs use powerful Mosfets without any resistors to limit the current.
    Leave the unused output with nothing connected to it and it will be fine.
     
  3. BobK

    BobK

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    Jan 5, 2010
    Do you understand why unused inputs should be grounded? Does that reason apply to outputs?

    Bob
     
    Harald Kapp and davenn like this.
  4. 73's de Edd

    73's de Edd

    2,871
    1,216
    Aug 21, 2015
    SEND THEM TO ME !
    I can dern sure use them . . . . they will be well received . . . and therefore, not be wasted.
     
    Richard9025 likes this.
  5. Audioguru

    Audioguru

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    Sep 24, 2016
    I don't have many unused outputs but instead I have a lot of amplifier power that is rarely used. I hate audio distortion and never play acid rock so I keep my amplifiers away from full power clipping. It would be good if I could save then later reuse the unused extra power.

    Remember when AA battery cells had a label on the side that burned to show the amount of charge left in them? If the test was done a more than a few times then it killed the battery almost like when people continuously short a battery to keep the electrons from leaking out.
     
  6. BobK

    BobK

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    Jan 5, 2010
    While we are on unused things...

    The X86 processors in our PC’s have hundreds of instructions, most of which are never used by the typical user. It would be nice if we could sell these on Ebay to people who need more instructions.

    Bob
     
    hevans1944 likes this.
  7. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    What about your wall outlets when not used. Do you 'ground' them?

    The short and sweet answer (to bothe questions) is: NO.
     
  8. Audioguru

    Audioguru

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    Sep 24, 2016
    The absolute maximum allowed output current of your 74HC163 is 25mA. But it has enough power to conduct 68mA into a shorted output which will destroy it. If you connect an output to ground (which is a logic low) but an input causes its output to try to go to a logic high then it will be destroyed.
     
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