[sdiy] CMOS chip questions

[Scott Gravenhorst]

Dan Snazelle <subjectivity at hotmail.com> wrote:
>
>what about if you need higher supply? (+12volts) is there any replacement for 74C??
>
>thanks

AFAIK, you're back to the CD4000 series which will operate from 3 volts to 15 volts.

>
>----------------------------------------
>> From: usenet at teply.info
>> To: synth-diy at dropmix.xs4all.nl
>> Subject: Re: [sdiy] CMOS chip questions
>> Date: Sat, 18 Jul 2009 14:49:17 +0200
>>
>> Am Saturday 18 July 2009 01:48:01 schrieb Scott Nordlund:
>>> 74HC is usually fine. I prefer 74HCT since its inputs are TTL compatible.
>>> If you need something faster, use 74AC. The problem with diode logic (I
>>> guess you're using diode resistor logic?) is that you can't really chain
>>> stuff together. The speed depends on your choice of diodes and resistors
>>> as well as whatever you're driving. I believe TTL circuits prefer pull-up
>>> resistors rather than pull-down (doesn't matter with CMOS), so this may
>>> limit your options in some cases.
>>>
>> I'll agree totally here, 74HC instead of CD4xxx is usually just fine unless
>> you really need the devices to withstand 15V Logic levels. And in the 74HC4xxx
>> series you'll get the very same pinout as the original CD4xxx devices, so
>> that is a non-issue as well. With most small-scale suppliers, 74HC has better
>> availability than CD4xxx anyways. When it comes to single gates, there are
>> such on the market as well. Okay, all i've seen are SMT devices, but when you
>> need to save real estate, i'd go for that anyways. It ain't no black magic. A
>> bit pricey in terms of $$/gate compared to the usual 4-gates-in-a-case stuff,
>> but a lot easier to work with considering all those design questions popping
>> up when working with discrete Diode-resistor logic. And: if you should happen
>> to not use some gate in a case, you'll most likely be better of with spending
>> a couple resistors and tieing those inputs to high or low.
>> Regarding 74HC vs. 74AHC vs. 74AC in most cases you're safe going for 74HC.
>> Coz, when you actually need the additional speed of 74AC and AHC compared to
>> plain 74HC, you'll know anyways. In all those cases with SDIY i've ever come
>> across, 74HC had plenty of speed and still loads of margin. It's not like
>> clock jitters of half a nanosecond would kill us here.
>>
>> HTH,
>> Florian
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