Re: [CAD_CAM_EDM_DRO] CMOS supply rails

In a message dated 11/4/2004 9:53:33 AM Central Standard Time,
ccq@... writes:

The original A and B series CMOS chips, as well as the C series, (74CXX)
have a plus Volts rating of +15 to +18 Volts. The HC series, (74HCXX), seems to
be much easier to find than the C series, but the only data I've been able
to find on them shows a +5 or +6 Volt supply rail. Does the HC series have
the same rating as the others, but use the +5 or +6 Volt numbers to show
compatability with TTL, or what?<<

The "old" 4000A series was "good to" 15 V. The newer 4000B series was "good
to" 18 V. I have NO experience with the 74Cnn series, so cannot comment on
that.

The 74HCnn series is rated to a "Max. Vcc of 6 VDC". It is "zenered" or
something making it useless above 6 VDC. I am too cheap to just TRY to fry a
gate and FF or two by raising the DC slowly on up to 7 or beyond, but I'm
BETTING at 6.55 VDC, the magic smoke leaves the chips! Perhaps some younger
tinkerer with money he hasn't yet found a slot for will do a "bench test" on quad
gates, dual FF's, maybe even a '4538 dual monostable, and let us all know,
by publishing here detailed lab-notes!

The neat thing about "HC" is, it is "compatible" with TTL, particularly
74LSnn, so one can often simply swap-out old TTL chips when repairing, updating,
etc. (assuming sockets! Unsoldering a 16-pin IC with intent to "save" the
PTH board onto which it was soldered does a number on my sensibilities!
EEEEEEEEEWWWWWWW!!!!!!!!!!!!!!!!!)

This is a GOOD point to discuss here, as I found years ago that my home-brew
CNC stuff works VASTLY more reliably and "noise-immune" if 74HC has been
used, rather than 'LS. I used 4000 series with success WHEN it "would go", but
that is not "swappable" with TTL, so it was often a pain in the gluteous!

Jan Rowland. This is my first post in MONTHS!!!!!!!





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