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Logic ccts

  1. Sep 21, 2009 #1
    What is the mean of " Effective logic inversion " ?
    Because I cant understand this qustion,

    " Describe briefly why there is an Effective logic inversion between logic level from a TTL IC and the LED load it drives? "
  2. jcsd
  3. Sep 21, 2009 #2
    Hello aspiralanka-
    One conceptual problem some students have with understanding TTL is that outputs are better as current sinking outputs than as current sourcing outputs. So driving a LED is better done by tying one end of the LED to +5 volts and the other to a TTL current sinking output.
    Bob S
  4. Sep 21, 2009 #3


    User Avatar

    Staff: Mentor

    ... and the "inversion" in your question refers to the fact that the drive of the LED is "active low". That is, the output of the gate is low (for the reason that Bob mentioned) to turn ON the LED.
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