[sdiy] Another new hard to find part....

[Scott Gravenhorst]

"Roy J. Tellason" <rtellason at blazenet.net> wrote:
>On Tuesday 06 July 2004 10:27 am, Ingo Debus wrote:
>
>> Logic ICs have been obsoleted all the time. Well perhaps not really
>> obsoleted, but they didn't make the transition to newer logic families
>> (from standard TTL to LS or HC).
>
>I actually have a bunch of the original "standard" TTL chips kicking around. 
>I'll use those when what I'm doing only involves some small number of them, 
>and the power requirements aren't going to matter that much.  I also have a 
>bunch of 74H stuff from a scrapped mini (A Burroughs B500 as I recall) but 
>most of them are marked with proprietary numbers and aren't going to do me 
>much good unless I find a cross-reference somewhere.
>
>What I don't understand is the point of numbers like 74HC4xxx,  where they're 
>(apparently?) giving you the function of a 4000 series part but putting a 74 
>in front of it?  Maybe I'm just missing the point as I have not yet seen a 
>databook for these newer families.

There are small differences.  For example, I just learned that the 74HC4046 is
basically the same as a CD4046, (micro power PLL), but the VCO in the 74HC part
tops out at a much higher frequency.  I haven't researched the whole family, but
would guess that there are performance advantages of many 74HC parts over
CD4xxxx.  Also beware the power requirements.  Some of the 74HC parts are 5 volt
limited.

>
>And I remember reading somewhere that the whole 4000 series was going away. Is 
>this the case?  If,  as I have the impression of but am not sure,  the 74HC 
>and similar parts will only work with lots lower voltage supplies,  that sure 
>is going to limit some options.  I kind of liked the idea of a logic family 
>which would run on 15V or so,  and sometimes even wished that it were higher! 
>(Like being able to run something off a split supply like what's typical for 
>op amps.)

Not only will CD4xxxx work to 15 volts (some parts to 18), they will also work
down to 3 volts.  I have run several CD4xxxx based circuits from +/- 8 volts
without problems.  I just make sure all of the parts in the design are speced to
18 volts.


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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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