[sdiy] LM555 mono stable question

Jean-Pierre Desrochers jpdesroc at oricom.ca
Sat Jan 18 21:57:42 CET 2020


That should be an easy one for you guys...

I'm working on a mono stable circuit using a 555.
Input: small low going  pulse (5v to 0,  5usec) on pin 2.
Output pulse: allways  .050sec  high going pulse (0 to 5v)  on pin 3
This is this circuit:
https://alxslvrmn.weebly.com/555-monostable-diagrams.html

I tweaked R1 & C1 to get this 0.050sec output pulses..
This circuit works pretty well if I keep the incoming pulses
periods higher than .050sec in this case..
If I go lower than .050sec between each input pulses it's understandable
The 555 pin 3 output does not stay high because of the 555 nature..
But is there a way to overcome this situation ?
Should I use another approach ? Using another IC than the 555 ?
In fact what I need is a pulsating.050sec  output that will stay high
If I exceed the .050sec input limitation here (lower input pulses period
than .050sec).
JP




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