Hi,
I need help here and don't know why the following solution came about.
Wanted: Input impedance Zin and v for Zin = 0!
I first formed the stitches and then wanted to change to U/I, since Zin=u/I.
M1: -U+ i*R1 +Um =0
M2: -I + i*R1 + i*R2 + v*Um =0
Unfortunately, I can't find the solution below. Can anyone help me?
Zin=U/I
(No Ratings Yet)
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Do this without mesh flows – you don’t need it or you don’t need it. there are not two stitches.
Consideration: For the Eing. Resistance you need the flowing current through R1.
Question: Does he also depend on R3? Isn’t the voltage at the top of the common point between R2 and R3 always equal to V*Um ? but it is only driven by V*Um and doesn’t appear at the entrance – so it doesn’t matter for the eing. Resistance.
A series connection of 2 resistors with a fixed voltage source on the left and a controlled source on the right.
Supplement/Interpretation:
If you use and re-form the expressions from the answer of Poseidon, you come for the condition V against (infinite) on the results:
*Output/Input=V*Um/U=-R2/R1 (OPV amplification with feedback)
* Rin=R1
*Um=0 (input voltage at OPV)
The circuit thus behaves in the event that V becomes very large and negative, as a Operation amplifier with negative feedback.
So it is classic inverter circuit, where R3 is nothing more than a connected load which has no influence on the gain.
First determine Um/Im = Zm. Here:
(i) = R2*Im + v*Um
This applies to Zm = Um/Im accordingly
Zm = R2 + v*Zm –> (ii) Zm = R2/(1 – v)
The input resistor Zin is thus the series connection of Zm and R1 and thus
(iii) Zin = Zm + R1 = R1 + R2/(1 -v)
So you just prescribed yourself with the “*”.
Therefore, Zin = 0 must apply
R1 + R2/(1 – v) = 0 <=> 1 – v = -R2/R1
-> v = 1 + R2/R1
Bonus questions to you: Why is v Zin equal to 0 for this value? What value does the voltage of the controlled voltage source have? What power is in this case emitted by the source with voltage U? And how large is the power output for the controlled voltage source? How is all this for Zin unequal 0? Would negative impedances Zin also be possible and what does this mean?