Question about diode logic gate

Discussion in 'General Electronics Chat' started by The King of Electronics, May 12, 2013.

  1. The King of Electronics

    Thread Starter New Member

    May 12, 2013
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    Hi everyone,
    why we use resister when we design AND/OR-logic gate ?
    [​IMG]
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    The resistor R presents a load.
    Without R (R = 0) you would destroyed the diodes whenever A or B is connected to GND.
     
  3. The King of Electronics

    Thread Starter New Member

    May 12, 2013
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    0
    This happen when we replace R with short circuit, what about replace R with open circuit ?:confused:
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    804
    The diodes would be off and you would have undefined output voltage.
     
  5. BillB3857

    Senior Member

    Feb 28, 2009
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    If you were to draw a truth table of the gate you show, and use Vcc to represent a logic 1 and zero volts to represent logic 0, it will become clear. Now, take the two diodes and turn them around and instead of having the other end of the resistor tied to Vcc, tie it to ground. What do you wind up with in that configuration?
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    Then the circuit will not work on its own but will rely on the load that it is connected to.

    (gees, I hate dangling prepositions.)
     
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