Trouble finding SMD 74HC279


I've designed my current project prototype using a couple of 74LS279 (quad s-r latch with active low inputs) chips among others. Everything works as it should but now I'm moving to actually build the final product. For power, speed and size considerations I'm moving to surface mount components and the 74HC family instead. Here's where the trouble begins. I'm having trouble locating SMD version of 74HC279 chips. It seems to be a discontinued product in many places for some reason. I know I could probably redesign the same funtionality with j-k flip flops instead but I haven't found a chip that had four of them in one package. I'm trying to avoid increasing the component count as space is very limited already.

So my question is does anyone know where I could find SMD version of 74HC279 in the UK or within reasonable postage charges? Would be equally appreciated if you can suggest a replacement part for it.

I think its one of those chips that never sold well and has more or less vanished - its a quad latch, but they aren't identical, which makes it rather odd.

The LS TTL version does seem to still be available:

Thanks Mark. I'm thinking if nothing else turns up I'll probably use just the DIP16 version of the 74HC279 which I was able to locate and SMD versions for the rest. I figured I could save a little bit of space if I soldered the DIP packages just like the SMD chips (i.e. not drilling holes but bending the legs to the side and soldering on the component side)...

Edit: Yes, the latches are not identical but you can treat them as identical if you just connect both of the /S pins together on the double input ones...

It looks like discrete SR latches are rarely used (I've never ever used one in any circuit I've built), yet they feature heavily in tutorials on logic gates!

DQ-flip-flops are much more useful in practice, and if you want a SR-latch a pair of NORs or NANDs can be used anyway (this I have done), usually you'll have a few spare such gates knocking around - so I can see why SR-latches aren't commonly employed.

Yeah. At least I know which chip not to use in the future :) Think I'll stick with the 279 for this project as it would require too many changes and a lot more testing etc to use anything else now.

you did not list a chip part number that you wanted.

the suffix AD offers a SOIC part.

Newark element14 SN74LS279AD has 49

Avnet Express : SN74LS279ADR - has 555 in stock

Farnell element14 SN74LS279AD has 102

Mouser SN74LS279ADE4 - 523 SN74LS279AD - 663

Digikey SN74LS279ADR - 720

not sure how many you need. or what country, so I used suppliers in asia, the us and eu.

I should have mentioned that digi-key lists the same part count for two different numbers. one is on a reel the other cut tape. because it seems they only have that quantity, they probably take from the reel and cut the tape. ergo, two different part numbers with only that quantity on-hand.

did you have a specific part number ? for SN74LS279ADRE4 Verical is showing 40,000 in eu and china.

man, I gotta quit hitting send…

Digi-key lists that part but has a 2,500 minimum

Thanks guys. I need the HC family. Not LS or 4000 chips.

kbrown: Thanks guys. I need the HC family. Not LS or 4000 chips.

please list a specific part number and not have people chasing down un-useable chips.

He did say "I'm having trouble locating SMD version of 74HC279 chips" - prefixes and suffixes beyond that are likely to be vendor specific.