Question on Ebers-Moll model

Question

I have what should be a simple misunderstanding of a piece of text from "RF Circuit Design" by Lugwig. I am not in a class, just self-teaching. This book has been quite helpful, and I have not found anything inaccurate in it (yet).

This is a large model for a BJT.

Here is a page:

It all is quite clear, except equations 7.10 and 7.11 seem opposite to me.

The Ie equation makes sense if we are dealing with electron flow, but the Ic equation makes sense if we are dealing with hole flow. (because the Ir and Ic arrows are opposing, so the If and Ie flows must be opposing as well, per the equations).

Any brief comments helping me to understand these two relations would be appreciated.

Answer 1

Notice the direction arrows on the diagram:

All terminal currents are taken as positive when going in to the terminal. This is a common convention in circuit theory, even if practically the emitter current will normally be flowing out of the terminal.

With this convention in mind, there's no discrepency between the two formulas and both are written in terms of conventional current. \$I_E\$ will have a negative value when the device is in the forward active or saturation modes of operation.