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This is the hybrid-pi model of an n-channel JFET.

An answer on here claimed that the only difference between p-channel and n-channel JFETs is that voltages are reversed. How would this apply to the hybrid-pi model?

I would guess that the model would be identical to the one above except for changing the sign on \$v_{gs}\$, so that the source is positive, gate is negative, and current flows from source to drain. But I don't have sufficient understanding to know if this is correct. Is it?

If so, what about the h-parameter model for bipolar transistors? What would differ between N-channel and P-channel?

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The claim for that answer is true. You should remember that the hybrid-pi, T or h models are small signal equivalent models where the small signal parameters are derivatives of the large signal model at a specific operating point. Since the derivative is a linear operator, the small signal model will encounter the same effect, of reversing the subscripts, or just negating the voltages.

You could simply modify the hybrid-pi model of the N-channel JFET as follows:

schematic

simulate this circuit – Schematic created using CircuitLab

You should note that this circuit would have been the exact equivalent to the model you provided if I swap \$ v_{sg} \$ with \$ -v_{gs} \$.

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