Do you think an LED is a resistor?

[Sredni]

Here
https://www.vishay.com/docs/29235/elecsimtoolkitvishaynlr.pdf
Go tell Vishay they are using an 'oxymoronic' terminology.
After all what could they know about electronic components?

Hit CTRL-F and search for the word "diode" in that document. There are only 3 occurrences of the word diode. In none of those sentences do they claim that a diode is a resistor. 

Well, up to a few posts ago, "nonlinear resistor" was an oxymoron, so it's progress.

Try this. Go here: https://automobiles.honda.com/ (or any other car manufacturer) and try to find a Formula1 race car for sale.
If you can't find it then Formula 1 race cars are not cars.

Helen is a woman, even if you don't find it in the list of women whose name starts with K, like Kate.

[MK14]

Just for anyone who is interested, the OP seemed to be talking about the topic of this thread, around a couple of years ago.

You can call it generalized Ohm's law.

There is a vicious rumor that diodes are not resistors, but they are resistors. They are nonlinear resistors (if we neglect the dynamic parasitics, of course and assume the exponential curve in the VI plane is what characterize them).
If you need to invoke the principle of authority to defend this assertion, you can always quote Chua, Desoer, Kuh, "Linear and Nonlinear Circuits". This is what I call "THE bible of circuit theory". It's not some high school or vocational school textbook for courses limited to the easiest circuits.

[fourfathom]

Is a dog a cat?

[Gyro]

Well, up to a few posts ago, "nonlinear resistor" was an oxymoron, so it's progress.

Try this. Go here: https://automobiles.honda.com/ (or any other car manufacturer) and try to find a Formula1 race car for sale.
If you can't find it then Formula 1 race cars are not cars.

Helen is a woman, even if you don't find it in the list of women whose name starts with K, like Kate.

After 8 pages, why are you folks continuing to feed this guy? 

Just for entertainment value?

[fourfathom]

Just for entertainment value?

Yes.

[MK14]

To the OP.
Are you sure you are talking about a 'normal' diode, and not a 'special' type of (apparently chaotic) diode?

You seem to have given too little information for me to be sure.

But, are you thinking of Chua's diode?

https://en.wikipedia.org/wiki/Chua%27s_diode

https://en.wikipedia.org/wiki/Leon_O._Chua

https://en.wikipedia.org/wiki/Chua%27s_circuit

[Gyro]

Just for entertainment value?

Yes.

Just checking, knock yourselves out then.

[Zero999]

I suppose a noisy reverse biased zener or BJT junction is a special type of resistor with a random element to it.

[Someone]

non linear system has linear approximation around a small operating point....

STOP THE PRESSES!

... oh wait, that's the underlying principle of how spice AC analysis works.

Small signal analysis has nothing to do with what we are discussing here.
The resistance I talk about is the static resistance, not the dynamic or incremental resistance of small signal analysis.

Try again.

That was your long winded and dithering proof:

So, we are now seeing the diode as a voltage dependent resistor. Let's see... what is the resistance 400mV? Let's zoom in:

[MASSIVE IMAGE]

I'd say it's about 23.2 kohm.
Let's see what is the resistance at, I don't know, 660 mV (about 5mA of diode current). We can compute it by hand of course, but on the graph we see it is 132 ohm.

[MASSIVE IMAGE]

Now, let's see if we can make something with these values...
[snipping conversational fluff]
Ok, exact same results, if we neglect a bit of rounding error in reading and setting the values.
Now, take your black boxes out of the fridge. Put the diodes D1 and D2, and the resistors R1 and R2 inside a black box each. Shuffle them around. And tell me: without looking inside the black boxes and without resorting to second order effects (like temperature dependence, or changing the other circuital parameters to change the operating points) can you tell me which are the diodes and which are the resistors, by simply measuring voltages, currents and powers?

So to try and claim you're not relying on the well known small signal AC parameters is plainly incorrect.

If you dont like relying on small signal characteristics, perhaps "try again" with your explanation/justification.

Again, small signal analysis has nothing to do with anything I have written in that post.
Nothing.
I zoomed in on the V-R characteristic to find an accurate value of the static resistance. Not the dynamic, or incremental, or small signal resistance.
Then I used the static resistance at a chosen voltage or current to choose the limiting resistor that would have set the chosen operating point.
Then I showed that using a resistor with the correct static resistance value would give the same variables in the circuit..
If you want to waste a bit of time you can create in LTspice a voltage controlled resistor that has the same R=R(V) dependence of a 1N4148. You will then see that it will behave (secondary effects apart) as a diode, confirming that it's the variable resistance. that gives a diode its behavior.

Go ahead and try.

Oh new words and definitions to play with. How about we take the IEEE dictionary as the authoritative reference:

static resistance (semiconductor rectifier device) (forward or reverse) The quotient of the voltage by the current at a stated point on the static characteristic curve.

small-signal resistance The resistive part of the quotient of incremental voltage by incremental current under stated operating conditions.

small-signal A signal which when doubled in magnitude does not produce a change in the parameter being measured that is greater than the required accuracy of the measurement.

As I said in my opening statement, you're just playing with small signal analysis a well known and entirely un-novel method. There is nothing interesting here as most anything can be described as a small signal resistor (with bounds on some other dimension). So you're still wrong and trying to twist definitions to your liking while ignoring the consensus and the established science.

[Sredni]

To the OP.
Are you sure you are talking about a 'normal' diode, and not a 'special' type of (apparently chaotic) diode?

I am talking about ordinary signal diode, power diodes, zener diodes, tunnel diodes.
Have any of you even opened the Science Direct link I gave before?

From here (a page that is apparently invisible to many browsers)
https://www.sciencedirect.com/topics/engineering/nonlinear-resistor

Nonlinear Resistor
Nonlinear resistors have a common characteristic that their constitutive relationships are described by nonlinear algebraic equations.
From: The Electrical Engineering Handbook, 2005
 

From: A.C. Fischer-Cripps, in Newnes Interfacing Companion, 2002
3.3.7 Log amplifier
A non-linear resistor is connected into the feedback circuit. In practice, this can be a diode, but a transistor connected as a diode is used since the forward biased transfer function is more accurately exponential. The exponential nature of the forward biased diode leads to a logarithmic decrease in gain of the circuit as the input signal is increased.



From: A Gavrilović OBE, in Electrical Engineer's Reference Book (Sixteenth Edition), 2003
32.6.3 Surge arresters
The zinc-oxide non-linear resistor material used in modern surge arresters exhibits a very high impedance at normal applied voltage whilst at a voltage only some 50% higher a very low impedance is provided. The extremely non-linear relationship between voltage and current shown in Figure 32.20, has rendered obsolete the spark gaps which were a feature of previous arresters based on silicon carbide.
 

From: I.D. Mayergoyz, W. Lawson, in Basic Electric Circuit Theory, 1997
EXAMPLE 5.5 A Voltage Regulator Circuit
Consider the circuit shown in Figure 5.31, where a load resistor RL is connected in parallel with a nonlinear resistor characterized by the v1(i) curve shown in Figure 5.32. This curve exhibits “voltage saturation.” In other words, it has an almost horizontal (flat) portion which starts from small current values. We would like to find all currents and voltages in this circuit.



[note1: you know what is that curious component represented by a resistor symbol with two lines? It's a zener diode. A special kind of nonlinear resistor]

[note2: the above book as a section titled "Non-linear resistive circuits" where nonlinear resistors are introduced and diode and zener diode are used as examples of nonlinear resistors]

From YIN Jijun, ... LI Peng, in Unified Power Flow Controller Technology and Application, 2017
6.1.1.2.4 Metal oxide surge arresters
Gapless metal oxide surge arresters are used in a UPFC. In the simulation model, they can be replaced by nonlinear resistors. The nonlinear volt-ampere characteristics of valves are shown in Fig. 6.5.



From: Nasser Tleis BSc (Hons), MSc, PhD, CEng, FIET, M-CIGRE, in Power Systems Modelling and Fault Analysis (Second Edition), 2019
10.4.8 Passive damped resonant limiter
Fig. 10.10 illustrates one phase of a three-phase damped resonant limiter circuit that uses only passive components.



The limiter consists of an isolation transformer whose primary winding is connected in series with the ac system and a capacitor is connected across its secondary winding. A nonlinear resistor, for example, a varistor, or a fast-closing triggered switch, is connected in parallel with the capacitor, and a damped tuned filter is connected in parallel with the capacitor/varistor. Under normal unfaulted system condition, the secondary circuit appears as a capacitor at 50 Hz that, when transferred to the primary of the transformer, is equal to and hence cancels out the transformer’s leakage reactance. Therefore, at 50 Hz, the limiter appears as a short circuit except for the resistance of the transformer.
 

So, I hope there will be no more discussion about the usage of the term "nonlinear resistor". It is not a novel invention by Chua alone. It is a well known and estabilished term that encompasses, among others, diodes, transistors connected as diodes, zener diodes, varistors, incandescent lamps, neon lamps, etc. etc. etc.

I think we are left with the doubt if nonlinear resistors are... resistors. No kidding.

[Sredni]

Oh new words and definitions to play with. How about we take the IEEE dictionary as the authoritative reference:

static resistance (semiconductor rectifier device) (forward or reverse) The quotient of the voltage by the current at a stated point on the static characteristic curve.

Yes, this is the only one I have used. Did you not realize it?

small-signal resistance The resistive part of the quotient of incremental voltage by incremental current under stated operating conditions.

small-signal A signal which when doubled in magnitude does not produce a change in the parameter being measured that is greater than the required accuracy of the measurement.

As I said in my opening statement, you're just playing with small signal analysis a well known and entirely un-novel method. There is nothing interesting here as most anything can be described as a small signal resistor (with bounds on some other dimension). So you're still wrong and trying to twist definitions to your liking while ignoring the consensus and the established science.

No, I have not used small signal analysis. Where did you study small signal analysis? You are mistaken. Please seek tutoring from someone you trust to straighten this out.

[Kim Christensen]

From: A.C. Fischer-Cripps, in Newnes Interfacing Companion, 2002
3.3.7 Log amplifier
A non-linear resistor is connected into the feedback circuit. In practice, this can be a diode, but a transistor connected as a diode is used since the forward biased transfer function is more accurately exponential. The exponential nature of the forward biased diode leads to a logarithmic decrease in gain of the circuit as the input signal is increased.

Notice that they didn't write this:

A non-linear resistor is connected into the feedback circuit. In practice, this can be a resistor, but a resistor connected as a resistor is used since the forward biased transfer function is more accurately exponential. The exponential nature of the forward biased resistor leads to a logarithmic decrease in gain of the circuit as the input signal is increased.

 

[Someone]

Oh new words and definitions to play with. How about we take the IEEE dictionary as the authoritative reference:

static resistance (semiconductor rectifier device) (forward or reverse) The quotient of the voltage by the current at a stated point on the static characteristic curve.

Yes, this is the only one I have used. Did you not realize it?

small-signal resistance The resistive part of the quotient of incremental voltage by incremental current under stated operating conditions.

small-signal A signal which when doubled in magnitude does not produce a change in the parameter being measured that is greater than the required accuracy of the measurement.

As I said in my opening statement, you're just playing with small signal analysis a well known and entirely un-novel method. There is nothing interesting here as most anything can be described as a small signal resistor (with bounds on some other dimension). So you're still wrong and trying to twist definitions to your liking while ignoring the consensus and the established science.

No, I have not used small signal analysis. Where did you study small signal analysis? You are mistaken. Please seek tutoring from someone you trust to straighten this out.

You live in a continuous world with no quantisation or noise? Perhaps in your world there is some difference between those. For those of us in the world I inhabit they are the same thing, an exact derivative of infinitely narrow width does not exist physically or in spice (which you chose to introduce). Both static resistance and small-signal analysis are a delta V on delta I.

[Sredni]

Notice that they didn't write this:

A non-linear resistor is connected into the feedback circuit. In practice, this can be a resistor, but a resistor connected as a resistor is used since the forward biased transfer function is more accurately exponential. The exponential nature of the forward biased resistor leads to a logarithmic decrease in gain of the circuit as the input signal is increased.

 

I don't know. Maybe they are used to specific names, like calling their wifes Helen and Kate, and not just "woman".
They are in good company, tho. For example Bharathwaj Muthuswamy and Santo Banerjee, in their "Introduction to Nonlinear Circuits and Networks", Springer (2019) say:

In order to be able to use nonlinear resistors effectively in a practical design, it is necessary to understand some basic properties.We will illustrate these properties by considering a prototypical example of a nonlinear resistor, the pn-junction diode (henceforth referred to as diode). Although we model diodes as nonlinear resistors, they are so important in circuit theory that they have their own symbol[...]

But, hey, what could they possibly know about circuits and nonlinear elements? They only wrote a book about them.
How many books have you written for Springer?

[bdunham7]

In order to be able to use nonlinear resistors effectively in a practical design, it is necessary to understand some basic properties.We will illustrate these properties by considering a prototypical example of a nonlinear resistor, the pn-junction diode (henceforth referred to as diode). Although we model diodes as nonlinear resistors, they are so important in circuit theory that they have their own symbol[...]

Um, yeah....I think they're right about that....hey, I think we have these things called linear resistors, also known as 'ohmic', and don't they have their own symbol and all that?  We call them, um, er, it's at the tip of my tongue....