# Simple amplifier circuit, norton, thevenin questions

I have the above circuits and I have some questions related to them:

1. I drew above the Norton and Thevenin equivalents where $R_{no}$ is the resistance of the whole amplifier circuitry, excluding the load. Are they correct?

2. Is $V_{th} = V_1$? If not what is it equal to and why?

3. I simulated the circuit and have two sets of values for $V_{out}$, $I_{load}$ and $R_{load}$. How can I go about finding $R_{no}$? I tried various approaches but none of them seem to work.

Here is one approach I tried:

$$V_{load} = I_{load} R_{load}$$ $$V_{th} = \frac{V_{th}R_{no}}{R_{no}+R_{load}} + \frac{V_{th}R_{load}}{R_{no}+R_{load}}$$ $$V_{th} = \frac{V_{th}R_{no}}{R_{no}+R_{load}} + V_{load}$$ $$V_{th}R_{load} = V_{load}(R_{no}+R_{load})$$ $$\frac{V_{load_1}(R_{no}+R_{load_1})}{R_{load_1}}=\frac{V_{load_2}(R_{no}+R_{load_2})}{R_{load_2}}$$

However for some reason I do not get the expected value for $R_{no}$ from this answer. I cannot see what is wrong with the derivation though?!

• Seems like something might be going wrong with how you are treating the opamp. Check this answer out electronics.stackexchange.com/questions/73292/… – Brendan Simpson Feb 25 '16 at 20:25
• @bss36504 So you mean $V_{out} =V_{th}\neq V_1$? I can see how that might make sense but it does not help me find $R_{no]}$ – 15yyyyy Feb 25 '16 at 21:29