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Electronics => Beginners => Topic started by: MathWizard on February 18, 2023, 07:38:52 pm

Title: Solved-What's so wrong with this AC model , no internal caps
Post by: MathWizard on February 18, 2023, 07:38:52 pm

I'm just calculating some ABCD paramerters for some amplifiers and I thought I knew this by now, but I can't figure out why the BJT sim, is so different to my AC model sim, just for a CE amp.

I my calculations for A and D match the model spot on, with and without the bypassed emitter, Iin should be 411nA. But the BJT model keeps giving a Iin value about 1.3uA, so ~3x bigger than my calc and the 2 models.

What little thing am I forgetting or overlooking this time ?

I have IB=756.9nA, and D=rm*Gin=3.836mA/A  for when RE/Ce is ignored


Would the hybrid-pi model with caps fix this? I'm ready to learn that again, I just never got to using it last time.

Title: Re: What's so wrong with this AC model ?
Post by: MathWizard on February 18, 2023, 08:06:20 pm

Ok so just adding 20p between base collector, and 1p on b-e, I get near 1.2uA Iin in the models, so ok I'll have to learn that stuff next.