After an absence, I've begun to re-read this design book again. I'm sure to encounter more, but this was where rather sizable errors crept inin, c. pg. 100.
First, in the 'Alpha and Beta' section (p. 94+), we learned to approximate the beta
when collector current isn't known, by using emitter current where β ≅ I.e ÷ I.b since normally β = I.c ÷ I.b
Discussion of
Common-emitter transistor configuration commences on p. 98. Base current controls product of transistor of this configuration, itself taken from Collector.
Be aware of transistor as current-controlled device. Although DC voltages fix its operating-point, where its Collector must be the most positive and its Emitter must be the most negative for the NPN being virtually boarded.
Summary of intentions:
Calculating base voltage and base current for a transistor under one of three configurations isn't a bad idea to learn. The text tries to show variables involved in a base voltage tally then goes in to conclude the formula with another quantity,
emitter current, I.e. And as both variables relate as matter of one compending formula's commutative attribute, any quantity I or V can be calculated for base or emitter. And then the approximation method shows how collector voltage or current can be calculated by swapping near-equivalencies, I.c for I.e.
Problem 1:
On p. 100, formula to calculate base-voltage leaves out the /β then puts it in again. Then variable for emitter current I.e
vanishes without rhyme nor reason from a stage of the equation.
Although I do not follow the math after mid-page, I grasp the upcoming switch from I.e ≅ to I.c ≅ after the produced equation.
Then the text goes on about leakage currents I.cbo and I.ceo. The text appears to be using the approximated formula for the beta. But the value can be calculated by referencing a chart that details I.c and corresponding I.b given V.cc value.
Problem 2:
For the text to introduce leakage current in this approximated way, it leaves me wonder whether it aims to be a fancy way to get the difference between I.c and I.e accounted for. But I tend to think not.
Yet we know the leakage current derives from there being some current that flows despite model for an ideal PN junction. Of course there is no trouble using what I presume to be "load line" charts to arrive at leakage current calculations. I think the references include "collector-base open" and "collector-emitter open," or open-beta and open-alpha currents, respectively. The author says that these matter in rarer designs.
