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SN75454B - isn't "on state" when transistor conducts current to ground?!?

Christopher Gecik
Prodigy 20 points
Other Parts Discussed in Thread: SN75454B, SN75453B

SN75454B.pdf

  • 0
    TI__Guru**** 153036 points
    Christopher,

    The PDF you attached is for the SN75453B not the SN75454B.
    The 53 is a OR gate so LED is OFF (output high) when either input is high.
    The 54 is a NOR gate so LED is ON (output low) when either input is high.
  • 0 in reply to Ron Michallick
    Prodigy 20 points

    Hi Ron,

    I thought I copied the truth table and simplified schematic for the SN75454 NOR gate.  I now realize that the NOR gate in the logic diagram led me to believe that I needed the SN75454.

    In the parameters table I now see that the part number I needed was the '53, actually an OR to give me the desired function table that looks like a NOR.

    The confusion I had was in looking at the truth table that looked like a NOR, but required an OR since inversion to a NOR is accomplished in the open collector output.

    Duh!  Study the data sheet BEFORE ordering.