How long can a cycle of the IC 555 be?

Thread Starter


Joined Dec 31, 1969
i know it depends on the the resistors and the capacitor, but in theory with 2 220K resistors and a 1500 microF you can get a 11 minuts cycle, is that near to what happens on implementation?

i'm using a diagram like this, and this formula.


John Luciani

Joined Apr 3, 2007
The timing equations are only valid for a range of R's and C's. IIRC 1500uF is outside
the valid range. You should check the manufacturer's datasheets for component

If you need that long a time period you may want to look at a counter.

(* jcl *)


Joined Sep 3, 2007
FWIW, I am trying to design a circuit that will stay on for a couple of hours... So far, upon testing, I have NOT connected the discharge, threshold or control voltage pins and it has been on for a couple of hours now...