4 ms·
Hayward's "more detailed model by Ebers and Moll" features prominently in AoE. So don't worry about them. The cardinal sin of teaching BJTs is to say that they
by exmadscientist 4y ago
Hayward's "more detailed model by Ebers and Moll" features prominently in AoE. So don't worry about them.
The cardinal sin of teaching BJTs is to say that they're current-controlled amplifiers: little current in, big current out. They are not, not really. They're voltage-to-current converters: little voltage wiggle at Vbe, big current wiggle at Ic. This is really not in dispute and anyone who tries to argue for the hFE/beta model as really true is wrong. Certainly, it is a useful approximation and often all you need, but it is not how a BJT really works and so don't pretend it is.
(The link between the two is that the base is not a high impedance input. That is pretty uncommon, so it's not surprising that it's kind of confusing! Because it's a low-impedance input, small changes in applied Vbe correlate directly with small changes in current, so it looks current-controlled. But careful measurements, as I believe are plotted in AoE, reveal the primacy of the Vbe-controlled model.)
- omnicognate 4y agoThanks! That's very helpful.
- gw99 4y agoThis is a really good description without delving into the mathematics.