thevenin prove question ..

[transgalactic]

here is how my prof taught me :
there is a system pi which is connected to a ressistor.
we replace the resistor with a current source
so the current which flows threw the ressistor did not change
and by some other law so does the voltage do not change on that branch.

and we replace every intial condition
which differs zero with independant source(capacitator which have v(t=0)=5 for example into capacitator v(t=0)=0 and voltage source 5volts)

now comes the problematic part
"we dissconeect the current source so we have Voc between those two points
from system pi,and then we turn every independant source in the pi system into 0
current source gets 0 current (open circuit)
voltage source is short circuit.

and we get some other voltage coming out of the pi system

and so by the super position law we sum them to gether and get thevenin law.

question 1:
when i hear superposition law i imagine a circuit which has two voltage sources
and we dissconnect one of the source and calculate what current flows on some ressitor

then we reverse the situation and we calculate again the current
and then we sum both currents
both half coexyst together.

the problem is that in my profs prove
there is no two coexysting parts

we have once voltage from pi
and the other votage from pi when all the intependant sources are zero

there is no super postion because those two situations are not on the same time
??

2.if we turn every initial condition differs zero into independant source
then when we turn every source to zero then there is no voltage at all

??

 

[Gary B]

Perhaps I can offer a slightly different explanation that will help you to understand what is going on. Any circuit no matter how complex can be replaced by a voltage source and a series resister. Think of a 12 volt power supply; rectifiers, filters and everything in it works exactly like a 12 volt source through a series resister the equivalent of the power supply’s impedance.

When he talks about removing the voltage source, he is saying that it has a resistance of zero and is calculating the value of the equivalent series resister for the overall circuit.