The Electrician
Active Member
Hello,
So you are saying that it doesnt fully respond to the OP's question because there were no parentheses in the denominator?
It wasn't because of "no parentheses" in the denominator. You said:
"If we look at the denominator alone:
D=R2*R4*RL-R1*R3*RL+R1*R2*R4
we have a couple choices with the main goal is to get:
D=R2*R4*RL"
You then made D=R2*R4*RL, showing your choice with parentheses. You said:
"We can then factor out R1:
R1(R2*R4 -R3*RL)=0
and we are left with:
R2*R4 -R3*RL=0"
That choice leads to a relationship between Vin and IL, namely "IL=Vin/RL". This condition (R2*R4 -R3*RL=0) provides that for a fixed Vin, the current IL depends on the value of RL. This is not how a current source driving RL should behave.
The OP asked if the circuit was a "voltage dependant current source" and you didn't show the condition (R2*R4-R1*R3=0) for the current in RL to be independent of the value of RL. For this condition the relationship IL = Vin/R1 obtains; IL does not depend on the value of RL.
Also, for that independence to hold, given an ideal opamp and R2*R4-R1*R3=0, if we remove RL and calculate the driving point impedance at the node which drives RL (with the Vin node grounded), that impedance should be infinite--the output impedance of a current source.
The condition you analyzed (R2*R4 -R3*RL=0), while interesting in its own right, does not provide an (ideally) infinite impedance at the node which drives RL when RL is removed. For a fixed Vin the current in RL is not independent of the value of RL; it varies inversely as the value of RL.
The OP asked if the circuit was a "voltage dependant current source"; it seemed relevant to point out the condition which would make it so, which you did not do. That's what I was referring to when I said that you did not "fully respond" to the OP's question.
I think that is very strange of you to say especially since R1 was factored out in later lines and the goal clearly pointed out. Perhaps you should re read my previous post.
It still reads the same as when I first read it.