I finally learned the basics of the hybrid T-model for BJT AC signals, so that's great. Say u have a BJT voltage reg. circuit, where the AC ripple from rectifier/filtering, is on the source voltages of everything. And have cap'a on the bases of BJT's. So ignoring the actual reactance of the cap, if u do small signal analysis with the model, u short the base. So there is no ac base current? Even tho I can see the voltage ripple. So it's common-mode,
Also in for instance a Colpitt's oscillator, where let's say a parallel tank circuit has C1 between B-E and C2 between E-gnd. Also the DC bias across the tank is usually always way way more than uV and mV considered in small signal analysis. So am I missing something or is this model is not for this case at all ?
Also I forget how I once did the loop gain of this type of oscillator, and I can't find the video, so I have to learn that I know. But in that analysis I was using the actual reactances, and I guess just the large scale BJT model ?
I have made a model in LTspice of my broken Tektronix 422 PSU, and it works quite well.
What of the small signal analysis can be applied to this ? Any where a BJT does't have a cap on it's base ?
Or should I be able to work out all relevant stuff from doing a massive mesh/node analysis with large scale BJT model, with common-mode AC ignored, is that right ?