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I am hoping that this is a very simple question. Circuit

I am trying to simulate the circuit in ngspice, but it seems that the oscillation will not initiate. I delayed the on pulse, but the expected 20Hz square wave does not appear.enter image description here I have spent an inordinate amount of time just because I am old stubborn. I might just have to build it first, but I am rearranging my stuff. Thanks a lot for your help. Note: the V1 pulse brings up the power supply after the simulation starts. talking electronics Circuit with a generic 555 timer. datasheet Circuit description from ICM7555.

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  • \$\begingroup\$ try this one ... electroschematics.com/8443/555-led-flasher \$\endgroup\$ – jsotola May 9 '18 at 3:59
  • \$\begingroup\$ Shouldn't there be a path from the discharge pin to ground somewhere? Otherwise, it'll just charge the capacitor, then switch to discharge mode but the current has nowhere to go... \$\endgroup\$ – Jules May 9 '18 at 4:30
  • \$\begingroup\$ Where are you getting your 555 model? I've had trouble with poor or non performance of 555 models in ngspice. \$\endgroup\$ – Brian Drummond May 9 '18 at 8:38
  • \$\begingroup\$ @Jules I believe here it's discharging the capacitor through the output pin, which isn't too unusual in 555 circuits. \$\endgroup\$ – Hearth May 9 '18 at 13:26
  • \$\begingroup\$ Some working ngspice examples: sourceforge.net/p/ngspice/discussion/ngspice-tips/thread/… \$\endgroup\$ – holger May 26 '18 at 21:40
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It really looks like a bad SPICE models in Ngspice, I simulated your circuit in LTspice with Bordodynov model library and it worked

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  • \$\begingroup\$ I tried it in ltspice and it worked fine. Thanks. ltspice makes it easy to initiate the oscillation. I tried another 555 model in ngspice to no avail. \$\endgroup\$ – Richard Anderson May 12 '18 at 21:23

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