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SN74LS04: SN74LS04

Part Number: SN74LS04
Other Parts Discussed in Thread: SN74LVC04A, SN74LVC14A, SN74HCT14, SN74HCT04


   I am using SN74LS04 for an on/off sensor detection, For some reason, my channel 1Y is not able to pull above 0.9V when my input 1A is 0V. If 1A is 5V, then my 1Y will pull low to 0V. I thought there is a leakage somewhere else, but all my other gate are 2A, 3A, 4A are working as expected with a identical circuit. All your inputs are greatly appreciated.


  • Hello,

    A couple comments:
    Is there a short on the output?
    Is the output pulling a lot of current?
    Is the input fully down to 0V at the device?
    These are a few things that could be messing up the operation of the device.

    If there really is no load on the output and the input is truly 0V, then possibly the device was damaged somehow.
    If so, does putting in a new device fix it?

    I would also recommend using a newer technology device that has better output voltage and drive characteristics such as the SN74LVC04A.
    or potentially using teh SN74LVC14A which is a schmitt trigger input device and would be tolerant to slow rising inputs if thats what might be causing the problem.

    Please let me know if you have additional questions, and I would be happy to help!
  • The devices I suggested before are CMOS devices that cannot tolerate 5V.
    If you need a device that can tolerate 5V and has TTL levels, then I would suggest looking at the SN74HCT14 or SN74HCT04.