Hi Everyone,
I was just about to put together a little lesson to talk about a simple astable multivibrator circuit that I am sure many of your have seen. The best example I've found of the circuit can be seen in the simulation found here:
http://www.falstad.com/circuit/e-multivib-a.htmlEvery time I've seen this circuit it's been explained to me that when one transistor charges up to the threshold voltage for the junction, current begins to flow from collector to emitter causing its corresponding cap to discharge. This flow kills the voltage at the base of the opposite transistor and the discharged cap now starts to charge in reverse to build the voltage back up at the base of that opposite transistor. What I never knew until today was that the voltage at that base does not go to zero volts when the switch occurs. It goes well into the negative voltage range (as seen in the simulation). I experienced this while bouncing around the circuit with my oscope.
For the life of me I cannot convince myself as to why the voltage would go into the negative. My formal electronics training was not so good and I feel like now is one of those times it's beginning to show. I've tried simplifying things experimentally to root out an explanation but I've had no luck so far. Thanks for any help you can provide.
-Skinny