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I have a choice between a CD4017 and a CD4017B.

I've also seen CD4026 and CD4026B.

What is the difference between these - is it a silicon revision or do they have different functionality?

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The letters can vary depending on the company, but usually they are a minor difference between. Have you checked the datasheet? – Kellenjb Oct 29 '10 at 14:38
But what datasheet? Many manufacturers make the same ICs. For example Fairchild I think make some CD series logic IC's. – Thomas O Oct 29 '10 at 14:40
I can find the datasheet for CD4026B types and CD4026 types but they don't seem to reference each other. – Thomas O Oct 29 '10 at 14:45
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I have actually told my students this a few times. If the manufacture you are using doesn't provide a datasheet to you, then you shouldn't be using them. – Kellenjb Oct 29 '10 at 14:56

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Quoting Wikipedia: "The original 4000 series was available in two versions: The A series was unbuffered, while the B series featured buffered inputs and outputs (in the form of additional, simple logic gates). The buffered outputs are able to source or sink more current than the unbuffered outputs, thus eliminating the need for discrete switching transistors in some designs."

I think it's pretty safe to say that the CD4000 number is the generic number, not caring about specific properties like buffered outputs, just the basic logic function. The suffix letter, according to wikipedia, will tell you about the output buffer. Further suffix letters (2nd, 3rd, ... letter) will tell you about packaging options and the like; this may differ from one manufacturer to another and is noted in the data sheet.

Today, only the B versions of the 4000 logic ICs seem to be available. At least that's what the manufacturers' websites tell me. Do you have a link for the 4000 (without B) series data sheet? Is there a manufacturer's logo on the chip?

It might be the case that some manufacturers produce the buffered version (-B), but mark the actual devices without the B. To be sure, you would need a data sheet that tells you the specifics about device marking code.

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I think it's changed over the last few years. I can't find any non -B IC's. What is the difference between a non-buffered IC and a buffered IC? I mean, both outputs are from the drain/source of the internal CMOS fets, so what would adding buffering to them do? – Thomas O Oct 29 '10 at 15:16
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The output (and, actually, input...) buffers might be built using larger FETs than those contained within the logic circuitry, allowing for higher currents or more precise thresholds. en.wikipedia.org/wiki/4000_series#Design_considerations, focus.ti.com/lit/an/scha004/scha004.pdf – zebonaut Oct 29 '10 at 15:22

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