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On 6/06/2024 1:46 pm, legg wrote:<snip>
>
If all the models with Tf<20ps are evaluated, you get unpredictable
results. Note that the bfr92a model doesn't actually meet this
limitation, but other similar models do (~bfr93). There are roughly
270 of them.
Each will either:
- fail to engage with the slow output detector.(31)
If they aren't fast enough to get triggered as emitter-coupled
monostable by a pulse that is 400psec wide at hallf-maximium voltage
of 100mV.
>- act roughly like the original simulation.(217)>
- oscillate at an unrelated frequency.(19)
Broad-band transistors will oscillate without a base-stopper of adequate
resistance - I tended to end up with resistors between 22R and 33R.
There are better solutions, but in the work I did it wasn't worth the
trouble of finding them.
>- stall.(1)>
Up the gain.
>- give incoherent wild results (2)>
Change the base-stopper resistance.
>http://ve3ute.ca/query/Tf_20ps_vs_bfr92a.zip>
Just why one model does one thing, while another does something
else might be interesting to figure out.
No model is perfect. If you model something and it seems to work, it's
worth putting together a real circuit (which takes longer) and seeing
what it actually does.
>
If it doesn't work, or doesn't work all that well. fiddling with the
model may point the way to something that might work better.
>
--
Bill Sloman, Sydney
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