No current limiter needed for 74XX chip input. Correct?

Discussion in 'General Electronics Chat' started by Mike C, Feb 11, 2015.

  1. Mike C

    Thread Starter New Member

    Feb 11, 2015
    6
    0
    I just wanted to confirm that I don't need a current limiting resistor on the input of a 74XX chip.

    I am currently testing on a 7404 and it seems to work fine if I connect up one of the inputs directly to the +5V power supply. Just wanted to make sure I am not risking burning out the chip. From what I can tell from reading the datasheets they have lots of internal resistors inside of them.

    Thanks and sorry if this is a complete newbie question.

    I have seen conflicting answers on the web.
     
  2. crutschow

    Expert

    Mar 14, 2008
    12,990
    3,226
    As long as the input voltage is between 0V and the supply voltage there is no need for a resistor.
    I know sometimes a resistor is recommended if the input is permanently tied high to protect the input from any transients spikes on the supply voltage but I think the chances of that damaging the input are small.
     
  3. Mike C

    Thread Starter New Member

    Feb 11, 2015
    6
    0
    Thanks for the response.

    I only have 1 voltage source (i.e. I use the same rail to power the IC and to supply the HI inputs to the ic) so I guess I am ok in that case?

    Thanks a ton
     
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