early voltage bjt
Hey there DarrenHeywood,
It was fun decoding your question - acronyms with an English spin.
For the uninitiated:
bjt = bipolar junction transistor
ce = common emitter configuration
early voltage = (I have no idea - maybe rising voltage)
whilst = while
Let's consider your first problem - you wrote:
"The only problem I have with that, is Thevenin's generators provides inherent boundaries whilst Norton's current generator does not."
Au contraire my friend. From a voltage and current viewpoint they are identical - perfectly identical in every way. Open circuit voltages are identical, short-circuit current is identical, internal resistance is identical - what more could one ask.
I hope you will reconsider your stance on this important issue.
Now let's look at your second conundrum.
Assume a supply voltage of 12.75 V. and a load resistor, RL, of 500 Ohms.
You can check my math, but I'll give you the results.
(Ic = 5.5 mA)
Power dissipation:
P(RL) = 15.125 mW.
P(CE) = 55.000 mW.
------------
P(Total) = 70.125 mW. This is the total power dissipated.
Now let's look at the Thevenin equivalent assuming 20K and -100V as you suggest.
P(20K) = 605 mW. This is the power dissipated in the 20K resistor.
This is not the same as P(CE). Could Thevenin be wrong?
No, not this time either. Here's the kicker - power sources PROVIDE power and are negative in the power entropy budget. So the power PROVIDED by the -100 v source is
P(-100V) = -550 mW. Note: not negative because of the negative in -100V
And total P(CE) - this is the power dissipated in the Thevenin transistor:
P(20K) = 605 mW.
P(-100v)=-550 mW.
-----------------
P(CE) = 55 mW. the same as the first
And we can all breath a sigh of relief.
Your method of using a base bias current is almost never used in simple ac amplifier design since the gain is then directly proportional to Beta which varies widely from unit to unit and with temperature, voltage and frequency. Usually the base is biased at some mid-voltage and the bias current and gain are controlled with an emitter resistor. But I assume you chose it to make the question clear.
Hope this helps.