How to make/describe an element with negative resistance of minus 1 Ohm?
My comments to SE EE question How to make/describe an element with negative resistance of minus 1 Ohm?
New intrigue emerged in EE... Let's see what will happen there...
My comments
- Do you really want to understand how to make a negative "resistor" with resistance -R? If so, think first and tell me what you want (can) use it for. If you can explain me that, you have done half the work...
- And what is the idea of this circuit? What does it do? What is the point of using it? I deeply doubt that the OP will understand something of what is written here...
- I agree with you... but my doubt was if OP would understand it. I perfectly understand you and know what is the point of this. But I know it from before. The idea of what we write here is OP not only to be able to make it but also to understand what he/she has made...
- Can you explain what it means "to get a negative number" in terms of circuits? What is it physically? What does it do? Why does it do it? Because here we are dealing with material objects - elements, circuits... something we can hold in our hands... If we were mathematicians - yes, but we are technicians and engineers...
- No, this does not explain anything useful to one who wants to make a negative resistor. To make sure of this, ask the OP to make a negative resistor according to your recipe. It is a recipe for mathematicians.They will even write, for their convenience, a/b = c and a/b = -c ...and will be happy...
- But still can you try to say it simpler and clearer what it means "the current to flow from the terminal with lower voltage to higher voltage" so that a 6-year old can understand you (Einstein:)?
- I think I understand what you mean about the incandescent lamp - that the current does not increase at the same rate at which the voltage increases (ie, linearly)... but slows down. Thus, the incandescent lamp approaches a current-stabilizing element which is a prelude to a kind of negative resistance ...
- Regarding the lamp, it stays in the middle of the evolution path from the ordinary ohmic resistance to the weird N-shaped negative differential resistance (NDR). The best way to explain what N-type NDR means is to follow the path "linear resistor" -> "constant-current nonlinear resistor" -> "N-type NDR". The lamp stays close to the constant-current resistor...
- Your requirements are great for our purpose - to understand what this strange thing negative "resistor" (circuit powered by its own source) is. But I didn't understand what you were going to use it for? This is important, firstly because there are different types of such resistors, and secondly, because it will be easier to guess how to do it...
- Let me guess... Homework? If so, and the teacher forgot to tell you what this -1 ohm resistor will be used for, try to find some need for it...
- I suggest first to clarify your problem here (and in the chat eventually) before I to write an answer (if needed). Agreed?
- Let's not deviate from the topic, which is very interesting from every point of view. (I think of OP because I am a teacher and that is my main task - to think about students. I think there is nothing wrong with that and to treat the questioners here as my students.)
- Maybe a research work on creative thinking for the purposes of machine learning:)? Anyway, the important thing is to reveal the idea behind the op-amp circuit in the Spehro's answer known as INIC (current-inversion negative impedance converter). I even suggest we consider its dual circuit - VNIC (voltage-inversion negative impedance converter); we can even ask him to put this circuit version (with swapped inputs). BTW last night I was very excited about the discussions here and couldn't sleep on Christmas Eve. My idea is to finally assemble an answer from these comments.
- The need for negative resistance can be derived from the classic power supply problem - the voltage drop across the wire. Imagine that you want to power a computer with 5 V at a distance and the wire resistance is 1 ohm. If the computer consumes 1 A, a voltage drop of 1 V will be lost on the line and there will be a voltage of 4 V on the computer... and it probably won't work. The obvious solution is to compensate for the 1 V loss by adding 1 V to the input voltage. The question is how to do it...
- We can do it in two ways. First, we can make the input voltage increase with 1 V by applying a negative feedback (the most widely used technique). Note the current can vary and so the voltage drop VR will vary as well... but the negative feedback will keep the input voltage always higher than the load voltage with VR. However, this requires additional voltage sense wire(s) for the feedback.
- The next technique, used in op-amp inverting circuits, is to add additional voltage equal to VR instead to increase the input voltage. This also requires additional voltage sense wire (to monitor the so-called "virtual ground"). Both these techniques use negative feedback. Here a question arises, "Is it possible to implement this voltage compensation without negative feedback? Let's think...
- The current flowing through the positive resistance R creates a voltage drop V = I.R and we have to neutralize it by an equivalent "mirror" voltage. We can create it by inserting a resistor with the same resistance in the line. As a result, the same voltage drop appears across it (the common current, like an "electric transmission" connects the two drops). Then we have to amplify two times the voltage drop across it and add it in series.
- Why two times? The one half will compensate the voltage drop across the new resistor, and the rest half voltage will represent the negative resistance. We can explain it in terms of resistances. By the amplifier with gain of 2, we have made a negative resistor with resistance -2R. It is summed with the positive resustance R and the result is a negative resistance -R.
Here my desire to continue on the topic began to run out and I stopped ...
Comments
Post a Comment