CD4043B-MIL: Is there a single channel small RS Latch out there?

Charlie Kupelian

Part Number: CD4043B-MIL
Other Parts Discussed in Thread: SN74LVC1G98, SN74LVC2G02, CD4043B, SN74LVC2G74-Q1

Is there a single channel small RS Latch out there? I just need one bit with no clock. Press one button, the output goes high, press the other button, the output goes low. 5 volt operation would be great. I could use a Dual NOR gate I suppose. Or even a D Flip Flop with Set and Reset inputs if I could find one with active high inputs. Anyway, if you were to build one, I would happily buy several hundred a year. If not, what is the most common work around? Thank you, Charlie

over 1 year ago

0 Malcolm Lyn over 1 year ago

TI__Mastermind 26290 points

Hi Charlie,

I think the most common work around I see with our devices is just making a set reset latch using a two channel nand gate. Here's a recent example:

(+) CD4093B-MIL: CD4093B configured as an RS Fip-Flop - Logic forum - Logic - TI E2E support forums

Best,

Malcolm

0 Clemens Ladisch over 1 year ago

Guru 317080 points

RS latches are not commonly used nowadays.

SN74LVC2G02 is a 5 V, dual-channel NOR gate. If you want Schmitt-trigger inputs (which is likely with buttons), use 2× SN74LVC1G98.

Is there a reason why you referenced a military-grade device?

0 Charlie Kupelian over 1 year ago in reply to Clemens Ladisch

Prodigy 70 points

I ramble, please be patient.

I have had a need for a simple RS Latch for decades. I ended up using the CD4043B which works great as a latch but it is huge and needs external circuitry to guarantee the power on state. It also has very low drive strength. It has also been around for decades and I fear obsolescence is coming soon.

What I really want is a 6 pin SOIC. R, S, VCC, GND, Q and notQ, that runs at 3.3 or 5.0 volts and can drive >10mA. Also a guaranteed power on state. I think if you built it, it would sell. You could charge a premium price? I know its worth a couple of dollars to me.

The military rating, no reason in particular. I do need Industrial, Automotive, or Extended Temp ratings.

Thank you.

+1 Clemens Ladisch over 1 year ago in reply to Charlie Kupelian

Guru 317080 points

I doubt there is much of a market. Nowadays, this is handled with a microcontroller.

0 Charlie Kupelian over 1 year ago in reply to Clemens Ladisch

Prodigy 70 points

thanks for the help. Looking through the posts in this forum, it looks like there are several questions about RS Latches. There is one from just 30 days ago.

anyway, I was just dreaming I guess. Cheers!

0 Charlie Kupelian over 1 year ago

Prodigy 70 points

This is a solution that I found to work for me. Using the sn74lvc2g74-q1 with the data and clock inputs grounded, the set and clear inputs are asynchronous and this does exactly what I want. Simple schematic for reference. Cheers, Charlie