This is another question from the series of "provocative" questions about the odd, exotic and paradoxical circuit solutions that should not exist but they still exist-:) I ask them with the purpose to look from another unusual viewpoint at the trite and banal circuit explanations and, in this way, to generalize and make eternal and immortal great fundamental circuit ideas. Thus we, educators, can arouse the curiosity in our students that is stunted as a result of the formal and heartless education...
Now about the question... It is more than obvious that we should apply the input voltage to the input of a voltage (tube, BJT, FET, op-amp, etc.) follower and to take the output voltage from its output. But what does happen if we, in spite of the tradition, apply the input voltage to the output of the voltage follower and to take the current flowing through "us" (the input voltage source) as an output? Is this arrangement (two voltage sources connected to each other) possible and correct from the basic electricity viewpoint? What would be the sense of this nonsensical connection? Can we use it somewhere in electronics? Can we see it in some existing circuit solutions? Can we see this idea in our life? Can we generalize it as a fundamental (particularly, circuit) principle?
I would like to give a hint with the attached picture. If this is not sufficient, look at the link below:
http://www.circuit-fantasia.com/my_work/conferences/cs_2005/paper1.htm
Do not consider them as an absolute truth; they show only my personal viewpoint at this phenomenon...
Trying to urge the discussion, I have attached a circuit diagram of such an arrangement...
If we take two ideal voltage sources generating different voltages and connect them in parallel, we are simply posing a contradiction in terms, and no solution exists for such a circuit. But if we also say that one or both voltage sources have a specified output resistance (non-zero), then the circuit can be solved.
If we consider the output of the emitter (or source) follower as a voltage source having finite output resistance, then the differential amplifier is one example of a practical circuit that connects two such voltage sources in parallel. Provided that the inputs are at the same potential, and the transistors are perfectly matched, the emitter current is the same in both transistors. If we consider a small change to the input potentials, so that there is now a small difference between the input potentials, the emitter of one transistor supplies more current, the other correspondingly less. The change in the current will be finite - standard texts present methods to calculate the corresponding change in the emitter currents.
Another practical example where two voltage sources are connected in parallel is where two amplifiers drive a load in a bridge configuration. Of course, in this case, the load itself provides the predominant current-defining element in the circuit.
These are fairly obvious examples, perhaps other contributers can think of others . . .
Daivd, thank you for starting the discussion! I would like only to add that here I mean voltage sources implemented as negative feedback circuits (i.e., amplifiers with a voltage negative feedback) that react to the external intervention....
Best regards,
Cyril
Are you trying to reverse the circuit, maybe like taking the input terminal as the output and vice versa .I am not sure, but something like reversible circuits, where the inputs can be traced back from the output
You can see also the new question about a specific circuit implementation (a common-base transistor stage) closely related to this question:
https://www.researchgate.net/post/Can_we_see_the_negative_feedback_principle_in_the_operation_of_the_common-base_stage_Can_we_think_of_it_as_of_a_disturbed_common-collector_stage
After more than one year maybe it is time to reopen the debate on this interesting topic? Here's an interesting application of this principle in the circuit of the current feedback amplifier (CFA):
https://www.researchgate.net/post/What_is_the_truth_about_the_exotic_current_feedback_amplifier_Is_it_something_new_or_just_a_well_known_old_Is_it_really_a_current_feedback_device?
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