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Other Parts Discussed in Thread: SN7414, SN74LS14, SN74AHC14


I am a hobbyist interested in a Schmitt-trigger / comparator IC to trigger a N-type power Mosfet to light some LEDs.

I came across the SN7414 Hex Schmitt-trigger inverter and I think it will work in my application.  I am somewhat new to electronics, and I don't understand the difference between the standard and "LS technology family" versions (SN74LS14).  Per the datasheet I see significant differences for the input voltage tolerance 7 vs 5.5V, and a difference in the current sink at threshold voltages.  Is there difference in the intended usage of the two versions of the the IC, or in general for LS vs. standard versions of ICs?



  • LS devices are a combination of the L (low-power TTL) and S (Schottky) families; they are both faster and use less power than TTL (see Wikipedia). TI does not have much documentation about this, but there's an appnote that tells you that ALS is much better than LS. Anyway, the different parameters are just a consequence of the different construction.

    However, these differences do not really matter: both the TTL and LS logic families are obsolete; they are sold only to support old hardware.

    Nowadays, one uses CMOS families such as LVC or AHC, i.e., SN74AHC14 in your case.

    See HCMOS Design Considerations, and the LVC Designer's Guide and the AHC Designer's Guide. An overview of current CMOS familes can be found in How to Select Little Logic (which applies also to the not-so-little chips).

  • Hi Stephen ,

    As Clemens rightly suggested , using CMOS parts would be better than the older LS (Low power Schottky ) and BJT devices.
    You can also consider AHCT which are TTL compatible parts .

    Clemens ,
    Thanks for the designers guide on the LVC and AHC . greatly appreciate your excellent contribution .