Electronics > Projects, Designs, and Technical Stuff

74HCT74 NXP vs Texas

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IDEngineer:

--- Quote from: Jan Audio on December 27, 2018, 04:14:09 pm ---the saw is also a slow ramp.
--- End quote ---
I have a remarkably similar situation in one of my existing designs, and I specified the 74AHC74 specifically because it has a Schmitt Trigger on its CLK input. There is also a 74AHCT74 version if you need the TTL compatible logic levels. A quick glance at DigiKey shows this part stocked in many thousands of pieces and available from at least two manufacturers. Cost starts under $0.25/100's.

Jan Audio:
Thank you Engineer, usefull information.

jmelson:
If you really need to work with 12 V signals, maybe you should use a 4000 series part.  I think the equivalent is a 4013, but the pinout will not be identical to the 74xx74.
These are much slower parts, and might work without additional components.  But, if a slow transition on the clock is the problem, then a Schmitt trigger on the clock is the very best solution.

Jon

David Hess:
Or use 74Cxx which is high voltage CMOS like the 4000 series but with 74xx pinouts and functions.

IDEngineer:

--- Quote from: David Hess on December 28, 2018, 08:36:49 pm ---Or use 74Cxx which is high voltage CMOS like the 4000 series but with 74xx pinouts and functions.
--- End quote ---
I had the exact same idea, but then I looked at specs and availability... the 74C74 is listed as "obsolete" from many manufacturers and the only one in stock (at DigiKey anyway) wants $7 each in low volumes. Also, the spec sheets I checked do not mention a Schmitt Trigger input on the clock, nor any other input.

There were other CMOS-based 74-series parts back in the day, so perhaps one of those is available and would work, but I'll leave such research as a worthwhile exercise for the OP. If he's got a $7 budget to solve this problem, my 25 cent recommendation and a couple of FET's would allow him to use 3.3 or 5V logic to control a 12V environment and still leave enough money for lunch.  :)

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