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Old 17th June 2013, 08:38 PM   #1
diyAudio Member
Join Date: Mar 2007
Location: California
Default HELP: TINA model of oscillator using 4093 not working. Desperate!!!

I'm trying to model a circuit that has a few 4093 NAND Schmitt triggers in it. I can't seem to figure out how to get the model working in TINA (Spice modeler from TI). I've seen the exact circuit modeled elsewhere on the web just fine, so I am really at my wits end here. I haven't modeled any logic circuits before now, so it could definitely be user error, but I am stumped.


Circuit and output are attached. It's right out of the datasheet! It should be a free running multivibrator but nothing is happening. I've included a timed switch so that pin 1 is pulled down to zero initially - that datasheet shows the transition low to high in case that was the source of the problem, but still nothing.

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Old 17th June 2013, 09:01 PM   #2
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Join Date: Mar 2007
Location: California
Ahhhhrrggggh. OK, I figured it out. I was simulating the circuit using the condition "zero initial values", which seemed to me to be the case since the circuit is "off" prior to simulation. If I just changed this to "use initial conditions" the circuit simulates as expected. Oddly enough, I haven't actually included any initial conditions for the circuit! How great is that, huh.

Anyway, now that I have much less hair remaining on my head, this annoyance has been solved.
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Old 2nd July 2013, 11:48 PM   #3
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Join Date: Apr 2011
Location: Pretoria
Yep, that cap needs to get charged to get the oscillator going.
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Old 2nd July 2013, 11:57 PM   #4
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Join Date: Mar 2007
Location: California
Originally Posted by ingenieus View Post
Yep, that cap needs to get charged to get the oscillator going.
No, the initial charge up wasn't the problem. No matter how long the sim time frame, there were no oscillations. As long as I used "zero initial values" it would not sim correctly. As soon as I switched to "use initial conditions" it worked as expected.
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