Not gate troubleshooting 74LS06N

Discussion in 'General Electronics Chat' started by holz1100, May 8, 2016.

  1. holz1100

    Thread Starter New Member

    Apr 27, 2016
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    0
    I am having troubles with the 74LS06N not gate.
    An input of 5v gives an output of 0.05v (correct).
    However, an input of 0.128v gives an output of 1.350v (not high enough)
    I am powering the gate with 5v. Any advice on troubleshooting?
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,634
    2,342
    Hello,

    Are you using pull-up resistors on the outputs?
    The 7406 is an open collector device:

    7406_internal.png

    Bertus
     
  3. dl324

    Distinguished Member

    Mar 30, 2015
    3,211
    619
    As @bertus mentioned, that device needs a pull-up resistor. The value depends on what the output is driving.
     
  4. holz1100

    Thread Starter New Member

    Apr 27, 2016
    14
    0
    The output is just fed into another logic gate (an AND gate). Any help in the way of how to calculate the pull up resistance value if i'm feeding into another and gate?

    Capture.PNG

    The switch by the not gate represents the input being either high or low
     
  5. dl324

    Distinguished Member

    Mar 30, 2015
    3,211
    619
    upload_2016-5-8_7-38-39.png
    upload_2016-5-8_7-37-29.png Assuming the AND gate is 74LS08, the maximum high level input current is 0.1mA and the minimum high level input voltage is 2V. The largest pull-up you can use is R = V/I = 3V/0.1mA = 30KΩ, but you could only drive 1 LS TTL load. LS gates have a fanout of 20, so I'd use nothing larger than 1.5KΩ.
     
  6. hp1729

    Well-Known Member

    Nov 23, 2015
    1,935
    218
    You need a pullup resistor on the output of the NOT gate to +V. 1K to 10K. The voltage you are reporting (1.35 or whatever it was) is the floating input of the next gate.
     
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