Help with LTSpice & 555 Timer

Thread Starter


Joined Dec 28, 2011
Hello everyone
Can someone explain to me why I can't build with LTSpice a simple Astable circuit with 2 resistors and a capacitor using the 555 that comes in LTSpice and be actually able to see the pulsed output on pin 3. I am a newbe to LTSpice and any spice program.
Thx in advance


Joined Mar 24, 2008
I do not use electronics simulators, but for some reason they do not do the 555 well, which is a bit strange sometimes. It is a frequent complaint.


Joined Jul 17, 2007
Hello Francisco, and welcome to AAC!

Unfortunately, you did not attach either your LTSpice .asc file, nor an image of your schematic (preferably in .png format).

SPICE programs can have difficulty with circuits that don't have a stable state. For circuits like that, on the Simulation Command panel, you can click on the box box to the right of "Start external DC supply voltages at 0v" to put a check mark in it.

That way the circuit starts off in a stable state; everything at 0v - and then the power is turned on.

There's another option; that is to check the box to the right of "Skip Initial operating point solution", and use .ic V(<node>)=voltage i(<reference designator>)=<current> etc. It's much easier to find node names if you use the Label command (click the [A] icon on the menu bar) and assign names to wires in your schematic. It also makes a lot more sense once you get the simulation running; labeled nodes will show up with your label on the plot instead of a relatively meaningless "N003" or the like.