IC difference

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

  1. bwaley

    Thread Starter Member

    Jun 1, 2008
    27
    0
    Help!
    what is the difference between 74xx,40xx,74Cxx,74HCxx series of ICs
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    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
    4,846
    63
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