555 Timer Help

R

RATabora

New Member

• Jan 23, 2009

• #1

Hey all,

This is my first post. Here we go!

I have about a 25ns pulse of 3.3V, that I want to delay to a 200ms pulse with a 555 timer. The problem I am having is that the 555 timer only accepts <2/3 of Vcc as a high output. I want to have anything >2/3 Vcc to give a high output. Does anyone know how to do that without introducing too many complicated parts?

Thank you!!

 

Hero999

Banned

• Jan 23, 2009

• #2

I think a 25ns pulse is too short to trigger a 555.

 

Boncuk

New Member

• Jan 23, 2009

• #3

Invert the +3.3V to trigger the timer at its trigger input with a low going pulse edge. Supply the timer with any voltage up to 14V to get the desired output level.

 

Hero999

Banned

• Jan 23, 2009

• #4

As I suspected it might not work.

EDIT 1
Found it!
EDIT 2
Better datasheet with a more clear graph.

The minimum trigger pulse width depends on the temperature and the amplitude of the trigger pulse. Look at figure 5, you'll be lucky if you can reliably get it to trigger with a 25ns pulse, may be you should try a CMOS version.
https://www.electro-tech-online.com/custompdfs/2009/01/CA555.pdfhttp://www.datasheetcatalog.org/datasheet/SGSThomsonMicroelectronics/mXuyztz.pdf

 

Last edited: Jan 23, 2009

Mikebits

Well-Known Member

• Jan 23, 2009

• #5

How about this part.
https://www.electro-tech-online.com/custompdfs/2009/01/74LV123_5.pdf

 

R

RATabora

New Member

• Jan 26, 2009

• #6

Wow thank you all! I will be looking into the 74LV123 for sure as it DOES seem that a 25ns pulse is too short for a 555 timer. Unfortunately I was basing the fact that it would work on a Multisim simulation.

I'll let you know how it goes!

 

R

RATabora

New Member

• Jan 26, 2009

• #7

Hmm, it appears that the 74LV123 will be perfect for what I need. But I can't find the spice model to simulate it!

I did however find the CD4538BC Dual Precision Monostable Multivibrator in Multisim. However, the min spec on pulse width on input is 35ns, so I believe the 74LV123 would be better.