Reducing Pulse Duration

A series cap into the gate, and a resistor from gate to ground, will do it, but the falling edge will be soft. That may or might not matter in your situation. It might be a feature!

Having done a bit of breadboarding I can see that's true about the soft tail off. However, a cap value of around 220nF provides a sharp enough drop for the first 20% or so of the input pulse's duration to fire a Schmitt trigger. I might even be able to get it down to 10% with a bit of careful biasing. That would certainly fall within the desired one-fifth to one-tenth range in theory. Not sure how reliable it would be in practice, though. :-/

Thank you, John. Some people here are using the word "differentiating" in the context of this thread. To me that word has only one interpretation (calculus) and it doesn't fit here. Can you or some other kind soul clarify, please?

It's that kind of differentiating, yes (approximately, of course).

The current in a capacitor is

I = C dV/dt.

So if you stick a pulse waveform on one end of a small cap, and load the other end with a low resistance, the resulting waveform is

Vout = IR = RC dVin/dt.

Cheers

Phil Hobbs

We engineers aren't too picky, so we call this a differentiator:

in--------C------+------out | | R | | gnd

with a not-so-small resistor, which just might be what he needs.

An RC feeding a schmitt will certainly work, but you may want more mosfet gate swing than 5-volt logic can make. Ancient 4000-series logic can run at 10 volts.

A proper one-shot and a gate driver may be the brute-force way to go.

A 555 could be used as the schmitt+driver somehow. Possibly three parts total.

All noted. Many thanks to all who assisted here.

It occurred to me while musing of the internal working of a 555 timer, that you don't need to differentiate the incoming pulse to make a pulse _shrinker_, see...

PulseShrinker.png

on the S.E.D/Schematics Page of my website.

(Funny square with X is just my "No-Float" symbol ;-) ...Jim Thompson

John, Surely you understand advertising strategy? Legwork means the viewer has to actually visit my page, rather than just clicking a link without seeing my other "teaser" circuits >:-}

Don't go old and cranky on me ;-) ...Jim Thompson

Austin Instruments wasn't to line your pockets?

And my post wasn't shit... It performed the function with less parts than your version... and it certainly won't produce any income on just that circuit alone.

Sheeeesh! I'm 76, feel like 40 ;-)

Cranky, cranky! ...Jim Thompson

No, I'm not as bad as Larkin... Larkin posts "circuits" with no way to prove they work. Everything I post works "right out of the bag".

And should go suck your thumb >:-} ...Jim Thompson

What? It works. Shame on you, John.

Sad how some people age poorly. ...Jim Thompson

That's a fake circuit and you cheated by specifying inordinately long 1uS r ise and fall times for the input pulse. The 555 would not respond to fast p ulse transitions, your circuit relies on the 555 recovering from RESET whil e the input trigger remains less than Vcc/3 long enough for TRIG to respond and trigger, otherwise it would remain locked up in off state. So the phon y circuit does require an RC on the pulse input to hope guarantee reliable operation.

Sheesh! You two remind me of this hilarious clip from Family Guy:

:-)

Fields is an idiot for complaining about having to push two buttons instead of one, that's lazier than George Jetson. Jim, do you remember me pestering you about being so cranky, maybe 3 to 5 years ago? You have certainly got over it. I suspect some major change in your life, or a change in some medicine, either dropped one that you were reacting poorly to or added one that helped. Care to expand? Either way, good!

btw, I was glad to get a reminder about the circuits you have posted.

If I post an idea, a circuit scribble, I have no obligation to prove it works; it may not. I generate a lot of ideas, and this is a discussion group.

If I post a Spice sim, it does what it does. I do post the Spice file, unlike some parties that only post the results.

If I post a schematic sheet from an actual product, which I do, I can assure everyone that it does work. And sell.

You're getting as crabby and crazy as JF. Do try to age gracefully.