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im having problems understanding the behavour of the hybrid parameter hre in the bjt AC model. im using the pi equivalent circuit to simulate the relation between hre and Ic (Dc value). i am not considering Rb Rex Rc or Ccs so the model is simplify to al the remaining elements Gray meyer AC equivalent circuit

my problem is that when comparing the graphic i obtain by simulating this equivalent circuit with the datasheet graph i dont understand why there is a change in the slope of the curve. im using the 2n3904 transistor parameters, down below i post the graph i obtain by aplying the gray meyer equations for the components values and the graph of the 2n3904 datasheet

Simulation with 2n3904 values Hre vs Ic curve

2n3904 datasheet Hre curve

im using the values of the spice models parameters that the datsheet of the 2n3904 provides as the data for my theorical model

Anyone has any idea whats effect is causing the change in slope? i could not find any information in electronics books or searching on the web

Sorry for my bad english Cheers!

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  • \$\begingroup\$ 1) The BJT's model is just that, a model, a model is always a simplification of reality. All models are wrong but some are useful. 2) since the difference occurs at the higher collector current, my guess is that some series resistances come into play that are not in the model. Try adding a few ohms here and there in the model and see what happens. \$\endgroup\$ – Bimpelrekkie Jun 4 '20 at 6:52

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