This discussion focuses on solving parts A and C of a circuit analysis homework problem involving an operational amplifier (op-amp) and a bipolar junction transistor (BJT). The voltage at Va is confirmed to be 4V, leading to the conclusion that Vin is also 4V due to the properties of negative feedback in op-amps. The participant is guided to apply Ohm's Law to find the current I1, with a calculated voltage drop of 2V across resistor R1 resulting in a current of 2mA. Nodal analysis is deemed unnecessary as the node voltages are already provided.
PREREQUISITESStudents and educators in electrical engineering, particularly those studying circuit analysis and operational amplifier applications. This discussion is beneficial for anyone seeking to enhance their understanding of circuit behavior and analysis techniques.
Well, yes, but you'll have to argue that based on the characteristics of an opamp with negative feedback. If you think in terms of the two golden rules of ideal opamp analysis..KTiaam said:
You know what the voltage is across R1. What about Ohm's law?KTiaam said:
Consider again the behavior of an ideal opamp with the feedback shown. It desperately wants to turn on that BJT hard, so it can reduce the voltage across its terminals to zero, but that really only requires the BJT to just barely move out of its cutoff region. You usually assume something about VBE then.KTiaam said:
milesyoung said:
The voltage (with respect to ground) at Vb is 6 V, and you drop down to 4 V as you cross the resistor to Va.KTiaam said:
so that means the voltage drop across the resistor is 2v, then using V=IRmilesyoung said:
Yes.KTiaam said:
Nodal analysis is useful when you need to solve for unknown node voltages, but you're already given the node voltages on either side of the resistor, so all there's left to do is just apply Ohm's law.KTiaam said:
milesyoung said:Yes.
Since Vb is at a higher potential than Va, what does that tell you about the direction of the current?