7555 vs 555

Discussion in 'General Electronics Chat' started by lokeycmos, Dec 10, 2010.

  1. lokeycmos

    Thread Starter Active Member

    Apr 3, 2009
    hello fellow enthusuasts, im working on a 555 based am transmitter. the author of the circuit said to use the tlc555(cmos) for the IC. my question is can i substitute a lm555? from what i could gather the timing resistors and capacitors my be affected? TY!
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    The output of the CMOS version is current compatable with TTL circuits. The TTL timer will draw much more current from the supply for its own operation, but other timing function values would be similar no matter which chip.

  3. Wendy


    Mar 24, 2008
    There are other issues besides. A 7555 might replace a TLC555, but even then there are differences between the two CMOS chips. For one thing the TLC is rated up to 2Mhz.

    A simple 555 can not go rail to rail, while all CMOS chips can. This may seem a subtle difference, but it can mean the difference between a circuit working or not.