Electronics > Projects, Designs, and Technical Stuff
74HCT74 NXP vs Texas
Jan Audio:
I have no zeners in house, another parts series to buy ?, do i really need them...
If the NXP was still available i would buy them.
I dont have software to render schematics, got any free ones ?, they should build it in this website one that locally generates on simple info.
NiHaoMike:
--- Quote from: Jan Audio on December 26, 2018, 01:55:08 pm ---I dont have software to render schematics, got any free ones ?
--- End quote ---
DaveCAD might be really limited in features, but is definitely the easiest to use.
Fork: https://github.com/scanlime/davecad
Original: https://github.com/EEVblog/DaveCAD
wraper:
--- Quote from: Jan Audio on December 26, 2018, 01:55:08 pm ---I have no zeners in house, another parts series to buy ?, do i really need them...
--- End quote ---
2 resistors for divider sounds too difficult? What's the point using capacitor to begin with?
Jan Audio:
The saw wave i put in now is from 6,6v to 11,5v.
SiliconWizard:
--- Quote from: Jan Audio on December 25, 2018, 05:02:40 pm ---Hi, sorry what is a PN ?
Texas is : SN74HCT74N
NXP : 74HCT74, i have to look.
--- End quote ---
Just take a look at the datasheets. The NXP one has a schmitt trigger in the clock input (actually most NXP logic parts have schmitt trigger inputs AFAIK), wheras the TI most likely doesn't (the DS doesn't make any mention of it).
NXP: https://assets.nexperia.com/documents/data-sheet/74HC_HCT74.pdf
TI: http://www.ti.com/lit/ds/symlink/sn74hct74.pdf
The lack of a schmitt trigger in the TI part makes the internal clock signal bounce in your case (it's not a digital signal with "clean" edges but an high-pass filtered signal.)
Don't remove the series resistor. You're going to kill the 74HCT74 eventually. If you didn't kill it yet, it's thanks to the high-pass filter which limits the duration of the 12V pulse and the internal clamping diodes. You may end up frying one.
With this kind of circuit, your best bet is to use a 74HCT74 with a schmitt trigger clock input such as the NXP one (I'm sure there are other vendors with this).
You could also add a schmitt trigger buffer in front of it, such as the SN74LVC1G17 (it's a single schmitt trigger buffer, the LVC series should be ok for your requirements and it's easily available whereas the 74HCT1G17 is not.)
If this was meant to be in a product, the second option would probably be better, because using a "standard" part (a reference available from many vendors) and requiring specific features in it from a specific vendor is a recipe for potential supply disaster later on.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version