Open Collector Logic?

I’m working on a somewhat hefty logic circuit, and I’m realizing that the design could be simplified significantly if all the gates had open collector outputs. I’m sure such things must exist, but I’m having the hardest time finding them.

Lets say I wanted a TTL level (74LS or similar) quad OR gate with open collector, or otherwise high-impedance rather than high outputs, what would I search for on Digikey?

I could just use a bunch of diodes I suppose.


Hey, Adam.

Don’t forget to look for “open drain”, too, since that’s technically the CMOS equivalent. OR gate options generally aren’t as plentiful as other gates (e.g. NOR); can you make do with something like the 74xx38 quad NAND gate?

- Jan

Thanks Jan, I see that there are more gates listed under “Open Drain,” but still no ORs. With NAND gates I would need to invert one of the inputs, as I don’t have control over it, but the other comes from my ATMega128 so high/low is my choice. It’s a shame, but I think diodes it is the way to go.

Well, of course with enough NAND gates you can do anything. If I was a real masochist I would just get a small FPGA!