With feedback around U6, there is no need for any Schmitt trigger gates; just about anything will work.

Yes.
The input inverter U6 could oscillate some during the input transition, but that wouldn't affect the delay or output waveform.

 

hi,
ak's circuit looks OK, Carl can you do a temperature run on that circuit and post the result.
E

 

Carl can you do a temperature run on that circuit and post the result.

Below, which shows about a 0.4µs change from 25°C to 75°C, but I have doubt that the model shows an accurate change in the Schmitt-trigger threshold with temperature, which is the main change that would affect the timing.

Certainly if you are concerned about the delay change with temperature, a comparator version of the circuit would likely be more stable.

 

hi Carl,
Many thanks for the test.
I must say many years ago when using CMOS Schmitt Gate timers, in wide temperature mobile environments, timing drift could sometimes be a problem.

Eric

 

when using CMOS Schmitt Gate timers, in wide temperature mobile environments, timing drift could sometimes be a problem.

Agree. In many applications, the only advantages of a 555 over other methods are the temperature stability of its two transitions levels, and that extra-beefy output stage. While it was the 555 that prompted my tagline, I do use them sometimes.

ak