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I found some nice circuits here as a pulse generators http://cappels.org/dproj/simplest_LED_flasher/Simplest_LED_Flasher_Circuit.html

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The author shows some scope pics and films from real world.. working. But when simulated in LtSpice... does nothing :(((

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What should be the problem? Thank you.

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This circuit will not work because the commonly used BJT's models in simulation tools do not support (model) the "avalanche breakdown".

You need to download the Bordodynov's lib available here:

http://bordodynov.ltwiki.org/

And used the avalanche BJT's.

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Additionally in real life, these circuits will not work with all small-signal NPN transistors. And will never work with PNP transistors. And it will not work with a low supply voltage. Therefore, you should treat these circuits as an interesting way of using the "parasitic properties" of BJT not intended by the designer. And this is for sure not a reliable solution.

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