IC difference

Discussion in 'The Projects Forum' started by bwaley, Jun 10, 2008.

  1. bwaley

    Thread Starter Member

    Jun 1, 2008
    what is the difference between 74xx,40xx,74Cxx,74HCxx series of ICs
  2. SgtWookie


    Jul 17, 2007
    74xx and 54xx series IC's are considered TTL, and generally need a Vcc of between 4.75 and 5.25v.
    4000 series are CMOS, and can generally use a Vdd from 3v to 16v; some higher and lower than that.

    The 74xx series generally consider a logic "0" to be anything below 0.8v.
    A logic "1" is anything above around 2.8v.

    CMOS will go from nearly Vss to Vdd on output swings.
    There are Schmitt-trigger CMOS devices that see input voltages below 1/3 Vdd as a 0, and above 2/3 Vdd as a 1. The rest of them aren't so forgiving; slow rise times can cause high frequency oscillations and overheating.

    CMOS device inputs must always have a path to Vdd or Vss. Letting them "float" is a recipie for disaster; they may oscillate at high frequency creating noise, or overheat due to operation in a linear mode.
  3. mik3

    Senior Member

    Feb 4, 2008