Hello,

I am studying Electronics in Romania and I have a LOT of trouble identifying the resistive elements that are part of a Negative Feedback Network, when given a circuit. I have a test in a few days and, for the life of me, I can't figure this out every time (I can, for the more obvious circuits).

So, for example, I have attached a kind of circuit that will most likely appear on the test. If I knew the resistors that are part of the feedback network, I would be able to tell what the feedback topology is.

Could anyone tell me which is the feedback network for my example and why? And also some tips on how to identify them?



Note: I had another test a few days ago and I added an extra resistance to the feedback network, so I'm really trash at this, for now.

 

Could anyone tell me which is the feedback network for my example and why?

The reason you are having difficulty is because that circuit does not have a feedback network.
It is operating open loop.
It consists of a differential input stage driving a emitter-follower output.

Negative feedback occurs when the output voltage of a stage or the amp affects the input voltage such as to reduce the gain of the circuit.
It also helps reduce any difference between the input and output waveform (distortion)

Here's a discussion of a transistor circuit with negative feedback which may give you some insight.

 

Hello,

Well there is feedback it's just not as apparent as it is when there is a separate resistor used just for feedback when there are already other resistors.

The feedback in a transistor amp with an emitter resistor is the emitter resistor itself. This may not be obvious at first but if we analyze the gain we see the gain goes down with an increase in emitter resistor when there is a collector load, and that the gain when there is an emitter load is a lowly 1 or less (voltage follower).
Note that with a series base resistor when the input voltage goes up it causes more base current to flow, but then the emitter current also increases, and that increase causes a rise in emitter voltage, and the input current comes as a result of the input voltage minus the base voltage divided by the base resistor, but the base voltage follows the emitter voltage to a great extent and thus we get the feedback due to the subtraction of the voltage caused by the emitter voltage increase. In a voltage follower this is in effect maximally, but in a collector loaded amplifier there will still be some gain greater than 1 in most applications.

This 'emitter feedback' acts as a stabilization factor the same way negative feedback works in a regular op amp circuit. If we had to make a flow diagram, it would have to show this feedback.

The question then is does the instructor want you to think about this or not.