Do you think an LED is a resistor?

[Sredni]

I am curious. How many of you people think an LED is a resistor? I should add: from the point of view of circuit theory, not from that of technology and underlying physics.

(This question originates from a question in another forum, where polls are not possible).

[switchabl]

Is this one of those trick questions where you pull a small-signal model out of your hat when everyone's distracted or explain later that when you said "resistor" you didn't actually mean resistor?

[xrunner]

No. It has a different name, so it is not a resistor

A rose by any other name ... ?

[hexreader]

This poll makes no sense

[Stray Electron]

  What a weird question.  And NO.  The answer to your question is in the last name of the part. The name that starts with a "D".

[switchabl]

"Aren't all memoryless, time-invariant two-ports just voltage dependent resistors in the end?"
- Gustav Kirchhoff, probably

[coppercone2]

its more like an antenna

[themadhippy]

There the cats whiskers when compared to many other illuminating devices

[Sredni]

Is this one of those trick questions where you pull a small-signal model out of your hat when everyone's distracted or explain later that when you said "resistor" you didn't actually mean resistor?

No, no trick question at all.
I can even show my hand: it is a resistor, a nonlinear resistor to be precise. Why? because its state is determined by the present values of voltage and current (and not their derivatives and integrals like capacitors, inductors, and memristors).

But a lot of people have trouble in recognizing that.

A diode is a resistor in the same way an incandescent lamp is a resistor. Both are nonlinear and both have exponential V-I characteristics. And yet everyone has no problem in computing power dissipated in circuits with incandescent lamp treating them as resistors, while when it comes to diodes the 'hard' exponential seems to create a mental block.

I just wanted to see how widespread this misconception is.

[CatalinaWOW]

When you use one word for everything you lose the ability to discriminate. 

Your construct is silly.  Or personal.  Most people have trouble determining power in non linear circuit elements because of the difficulty in determining the operating point.   While it is simple to do with the linear time independent component normally called a resistor.

[Sredni]

Well, if you give a circuit with a 12V battery and a 20W lamp to any high school student, they will immediately find the operating point and the resistance of the lamp. Is the lamp a resistor? Of course it is.
And yet the resistance is non linear, and the value found is Vop/Iop and has nothing to do with the local slope of the vi curve. But it is the resistance shown by the device in the circuit.

But for some reason, if you give a diode (and a means to determine the operating point), even if you end up doing the same thing, finding a resistance that has nothing to do with the local slope of the vi curve, there seems to be a mental block to accept that as the resistance shown by the device in the circuit.


Maybe it is due to the fact that in small signal analysis we use the differential resistance rd, and since this is different from the Vop/Iop value found, this latter value is not considered a resistance?

[CatalinaWOW]

The answer is in your comment.  When you specify 20 W incandescent lamp you set the operating point.  I think if you gave your students a 10 mW LED they might do better.

[Zero999]

The poll is missing an option: this is a troll poll. 

A resistor is designed to have an Ohmic response i.e.the current is proportional to the voltage. An LED is a type of diode, which in this case is meant to produce light so the voltage, current characteristicis unimportant.

[Bud]

A Resistor is reciprocal. An LED is not reciprocal.

[Sredni]

I assure you, this is not a troll post.
From the point of view of circuit theory, a diode IS a nonlinear resistor. Period.
You can read, for example, Chua, Desoer and Kuh, "Linear and nonlinear circuits". Top level authors and respected university level textbook.

I can go even further: a transistor is a resistor. It is a nonlinear, multi terminal resistor. And I guess this notion would encounter even more... resistance than the diode one. (I was kind of surprised when I first heard about it, but then when you reason about it it becomes clear why it is so - if we neglect parasitic effects).

As I said before I just wanted to see how widespread this notion is (even with a small population sample).

For example, in this other forum (or whatever it is called) it was argued that you can't use a multimeter measure the resistance of an LED because "it is not a resistor", while in fact the incapability to return a value is that at the small testing current used by the DMM either the voltage had to exceed the compliance of the current source, or the resistance to measure would be out of range.

[Sredni]

A Resistor is reciprocal. An LED is not reciprocal.

A linear resistor is reciprocal.
A linear resistor show direct, bilateral proportionality between voltage and current. A nonlinear resistor does not.

Are you arguing that nonlinear resistors are not resistors?
Or that nonlinear resistors do not exist?

[fourfathom]

Is the OP deliberately trying to confuse students? A diode has resistance, but that doesn't make it a resistor.  Eliminate the "time invariant" part and you can call a capacitor a resistor. 

[switchabl]

In the case of the incandescent bulb, the resistance is meaningful in the sense that it is the physical resistance of the filament contained inside (at the operating temperature). If you were to heat filament externally and measure again with a small test current, you would get the same result.

But even so, when it comes to circuit analysis, this value is not particularly helpful. The small signal resistance on the other hand happens to change relatively slowly throughout the hot/"on" region (the resistance change is only about ~P^0.25 due to the Stefan-Boltzmann law). So it actually predicts even larger shifts in the operating point reasonably well.

You are of course free to define a nominal resistance for the LED at a particular operating point. I'm just not sure what you would do with it. If it is for quick-and-dirty circuit analysis, approximating the LED as a voltage source is usually the most helpful option.

[Bud]

A Resistor is reciprocal. An LED is not reciprocal.

A linear resistor is reciprocal.
A linear resistor show direct, bilateral proportionality between voltage and current. A nonlinear resistor does not.

Are you arguing that nonlinear resistors are not resistors?
Or that nonlinear resistors do not exist?

A Reciprocal 2-pole means properties are same in both directions. Show me LED resistance being same in both directions.

[Sredni]

A Resistor is reciprocal. An LED is not reciprocal.

A linear resistor is reciprocal.
A linear resistor show direct, bilateral proportionality between voltage and current. A nonlinear resistor does not.

Are you arguing that nonlinear resistors are not resistors?
Or that nonlinear resistors do not exist?

A Reciprocal 2-pole means properties are same in both directions. Show me LED resistance being same in both directions.

How could I? A diode is a NONlinear resistor with an exponential characteristic and as such it is not reciprocal.

[IanB]

An LED behaves as a resistive component in a circuit because its instantaneous power dissipation is equal to the instantaneous product of voltage and current. It has no significant reactive component in its circuit behavior. In contrast, capacitors and inductors have reactive (energy storage) behaviors that dominate over the resistive contributions.

An LED is not "a resistor" (that word being reserved for components whose resistance is substantially constant), but it does behave resistively.

[schmitt trigger]

A resistor has an identical resistance value for both DC and AC voltages (disregarding real world parasitics). Simple as that.
An incandescent light bulb is a temperature dependent resistor, but the temperature rise is identical for DC and the same AC RMS voltage.
Another way of viewing it: a resistor has unity power factor.
A diode or LED doesn’t have those properties.

I know that this explanation won’t deter you from asserting differently. If you want to believe that…Be my guest. But please don’t attempt to convince us of your superior knowledge. It’s pedantic.

[IanB]

Another way of viewing it: a resistor has unity power factor.
A diode or LED doesn’t have those properties.

Can you show that an LED does not have unity power factor?

[Sredni]

Is the OP deliberately trying to confuse students? A diode has resistance, but that doesn't make it a resistor.  Eliminate the "time invariant" part and you can call a capacitor a resistor.

No, a capacitor is a circuit element that relates charge (the integral of current) to voltage. It can be time-invariant in the sense that its q-V characteristic does not change with time, still remaining a dynamic element.

And to answer other objections: sure, all components have parasitic elements but we name them in base of their dominant trait. A capacitor has significant capacitance and negligible esr and inductance. And a resistor has dominant resistance (even if it is 0.1 ohms) compared to the reactances of its capacitive and inductive parasitics at the operating frequencies.

In all this discussion I am assuming zero parasitics.
And no, the resistance offered by a diode is not a parasitic or second order effect: it is ALL it does.
Small resistance (not incremental resistance! Resistance plain and simple) when forward biased; large resistance when reverse biased.

[CatalinaWOW]

I assure you, this is not a troll post.
From the point of view of circuit theory, a diode IS a nonlinear resistor. Period.
You can read, for example, Chua, Desoer and Kuh, "Linear and nonlinear circuits". Top level authors and respected university level textbook.

I can go even further: a transistor is a resistor. It is a nonlinear, multi terminal resistor. And I guess this notion would encounter even more... resistance than the diode one. (I was kind of surprised when I first heard about it, but then when you reason about it it becomes clear why it is so - if we neglect parasitic effects).

As I said before I just wanted to see how widespread this notion is (even with a small population sample).

For example, in this other forum (or whatever it is called) it was argued that you can't use a multimeter measure the resistance of an LED because "it is not a resistor", while in fact the incapability to return a value is that at the small testing current used by the DMM either the voltage had to exceed the compliance of the current source, or the resistance to measure would be out of range.

You don't even follow your own rules. A DMM does measure the "resistance" of a diode, including Leads AT THE OPERATING POINT DEFINED BY THE DMM'S DESIGN..  No confusing nonsense about compliance points etc. 

This is why the definition of resistance you propose is not particularly useful.

[Sredni]

A resistor has an identical resistance value for both DC and AC voltages (disregarding real world parasitics). Simple as that.
An incandescent light bulb is a temperature dependent resistor, but the temperature rise is identical for DC and the same AC RMS voltage.
Another way of viewing it: a resistor has unity power factor.
A diode or LED doesn’t have those properties.

You are differentiating between resistors with linear, nonlinear symmetrical and nonlinear asymmetrical characteristics. A linear resistor and an incandescent lightbulb have symmetrical VI chars , a diode does not have a symmetrical VI char.

And no, it is not MY knowledge. I have given a well respected reference for that.

[bdunham7]

I can even show my hand: it is a resistor, a nonlinear resistor to be precise. Why? because its state is determined by the present values of voltage and current (and not their derivatives and integrals like capacitors, inductors, and memristors).

You could distinguish between resistors and nonresistors just based on your stated criteria, but then neither actual resistors nor LEDs would qualify since their previous history determines their thermal profile (temperature and internal gradients) and probably other things--thus their states are not determined solely by present values.  Also, you'd have to define the range of time, current, voltage, frequency and temperature values that apply to your attempts to classify the LED.  Depending on other parameters, an LED could be a capacitor or inductor, a photocell, a detonator or an antenna.  And so on.

But a lot of people have trouble in recognizing that.

I just wanted to see how widespread this misconception is.

Some ways of understanding things are more useful than others.  I think most of us understand the operation of an LED well enough to fully utilize and accomodate its characteristics without classifying it as a non-linear resistor.  Can you explain how considering it a non-linear resistor is helpful?

[Sredni]

For example, in this other forum (or whatever it is called) it was argued that you can't use a multimeter measure the resistance of an LED because "it is not a resistor", while in fact the incapability to return a value is that at the small testing current used by the DMM either the voltage had to exceed the compliance of the current source, or the resistance to measure would be out of range.

You don't even follow your own rules. A DMM does measure the "resistance" of a diode, including Leads AT THE OPERATING POINT DEFINED BY THE DMM'S DESIGN..  No confusing nonsense about compliance points etc. 

This is why the definition of resistance you propose is not particularly useful.

Of course it measures the resistance at the DMM operating point. The DMM returns a single value and since the resistance has infinite values (unlike in the linear case) you have to select one.

If you want to know the resistance (not the incremental one) offered by a diode in a circuit you can use load lines.

Oh, BTW, the same is true for the threshold voltage of a diode (which has infinite values as well) or the hFE of a transistor.

[bdunham7]

Can you show that an LED does not have unity power factor?

PF is calculated over time, at least a complete cycle of AC, otherwise it is meaningless.  Do you think an LED will have a unity power factor with an applied AC voltage with a peak greater than its V_f?

[Zero999]

Another way of viewing it: a resistor has unity power factor.
A diode or LED doesn’t have those properties.

Can you show that an LED does not have unity power factor?

Only linear resistive loads have a unity power factor. An LED is non-linear, so it will not have unity power factor.

[magic]

Here's another one:

I think it's obvious that MOSFETs are resistors too, but are they current controlled or voltage controlled resistors?
I think they are current controlled, because without current flowing to the gate their resistance doesn't change.

Would you agree?

[Sredni]

I can even show my hand: it is a resistor, a nonlinear resistor to be precise. Why? because its state is determined by the present values of voltage and current (and not their derivatives and integrals like capacitors, inductors, and memristors).

You could distinguish between resistors and nonresistors just based on your stated criteria, but then neither actual resistors nor LEDs would qualify since their previous history determines their thermal profile (temperature and internal gradients) and probably other things--thus their states are not determined solely by present values. 

Well, that is true for everything. In all circuit theory textbooks the essential traits of a components are isolated, and the secondary effects are neglected (until later chapters where all effects are combined).
I mean, this is the ordinary way of teaching circuit theory everywhere:

Resistors, it's voltage vs current
Capacitors, it's voltage versus charge
Inductors, its flux versus current
Memristors, usually not mentioned (but its flux versus charge)

But a lot of people have trouble in recognizing that.

I just wanted to see how widespread this misconception is.

Some ways of understanding things are more useful than others.  I think most of us understand the operation of an LED well enough to fully utilize and accomodate its characteristics without classifying it as a non-linear resistor.  Can you explain how considering it a non-linear resistor is helpful?

I am a black swan hunter, and misconceptions like these are the main food of black swans. I see this as a failure of connecting the dots between different chapters of the same book: it is in a separate chapter, it has a different name, so it has to be something different. Nah, it's just in a different chapter and has a different name.

(Minor) case in point, in this other venue it was stated that the DMM could not read the resistance of the diode (alone) because the diode is not a resistor (I have to double check the phrasing). This is a misunderstanding of the nature of the component and of the operation of the DMM.

[Rick Law]

All these times, I thought resisters are those who fight against the enemy while under enemy occupation....

This is a language/semantic issue.  Meaning of words varies from group to group, region to region, country to country.  In Europe, I may well want "Gas" in my bottled water.  In the USA, I would prefer "sparkle" or "carbonated water".  You put "Gas" in your car, and expel "gas" when you eat certain food.

This as an electronics forum, one can take some assumptions -- but this forum has such wide audience that if one wants that language precision, one must express it so or request it so.  Otherwise, with such wide audience, it would be merely "precision leaning" but not "precision conforming".

Precision use of language has it minuses.  I think those trained in engineering or physical sciences have a tendency to demand the same precision in wording from others.  This may be why in most businesses-side folks and tech-side folks don't communicate well with "the other side".

[bdunham7]

This is a misunderstanding of the nature of the component and of the operation of the DMM.

No it isn't a misunderstanding of that sort at all but simply a different use of the terminology, an assumption that the terms resistor and resistance mean simple linear resistance that heeds Ohms law.  A VI curve gives you a good understanding of the nature of the component even if you don't use the term "nonlinear resistor". 

[bdunham7]

I am a black swan hunter, and misconceptions like these are the main food of black swans.

You think that some calamity will result because an otherwise qualified engineer that understands the VI curve of an LED is going to make some ridiculous error because they don't consider the LED to be a resistor?  I asked you how this revelation that LEDs are actually (nonlinear) resistors could be useful.  Could you be less grandiose and more specific? 

[bdunham7]

All these times, I thought resisters are those who fight against the enemy while under enemy occupation....

Then the LED is a "collaborator"--it pretends that it will resist and then capitulates.

Precision use of language has it minuses.  I think those trained in engineering or physical sciences have a tendency to demand the same precision in wording from others.  This may be why in most businesses-side folks and tech-side folks don't communicate well with "the other side".

Actually I think the precision wording is more important in a legal setting where the words are literally the substance.  In physical sciences, I think one indicia of intelligence is when one can recognize concepts and principles when they are phrased differently or use different terminology.  In the metrology forum we can't even agree on what "calibration" means and there are reliable reference sources that differ on that matter.  There's no need to agree as long as you're clear on which definition you mean.  In physical sciences, words are describing a very precise reality as best we can and there's not one absolutely correct way of doing it.  There may be well-established conventions, but that's a different matter.

[Sredni]

I don't consider this to be a mere semantic issue. It is the signal that something is amiss in the educational process.
It reminds me of that chapter in "Are you joking Mr. Feynman ?" when Feynman was in Brazil and found that physics education there was fundamentally notionistic.

The diode-resistor issue seems to point to a compartmentalized knowledge problem, where the student is not able to generalize a concept learned in a previous chapter (or course) because nobody has connected the dots for him/her.

[magic]

I think it simply is a matter of the ratio of voltage and current through a diode never being important for anything practical, unlike in a resistor, hence no one cares about it.

If anything, it's dynamic resistance which may matter. Some diodes even specify it in the datasheet (at some nominal bias current).

[IanB]

I don't consider this to be a mere semantic issue. It is the signal that something is amiss in the educational process.
It reminds me of that chapter in "Are you joking Mr. Feynman ?" when Feynman was in Brazil and found that physics education there was fundamentally notionistic.

The diode-resistor issue seems to point to a compartmentalized knowledge problem, where the student is not able to generalize a concept learned in a previous chapter (or course) because nobody has connected the dots for him/her.

But what is amiss? What dots are not joined up?

A resistor is a circuit component with the primary purpose of acting as a resistor. A diode (LED or otherwise) is not such a component.

A resistor is a component with a power factor of unity in an AC circuit. A diode does not meet that criterion.

What I might grant you, is the often stated idea that a diode can magically drop 0.6 V in a circuit. What can be missed about this is the fact that the diode will necessarily dissipate heat equal to 0.6 V times the current flowing. The voltage drop is not "magic", it is resistive in nature.

[bdunham7]

I don't consider this to be a mere semantic issue. It is the signal that something is amiss in the educational process.

Could you be less grandiose and more specific?

[schmitt trigger]

Can you show that an LED does not have unity power factor?

. Power factor has two components, displacement angle and distortion.
An LED used as a load fed with an AC voltage, will rectify and distort the current waveform.

[Sredni]

I don't consider this to be a mere semantic issue. It is the signal that something is amiss in the educational process.

Could you be less grandiose and more specific?

I did, in the post you are quoting.
The inability to generalize a concept, namely the concept that resistors are described by voltage-current characteristics that do not need to be linear (nor symmetric).

[SiliconWizard]

its more like an antenna

Yes, an antenna that captures dark energy.

[Sredni]

A resistor is a circuit component with the primary purpose of acting as a resistor. A diode (LED or otherwise) is not such a component.
-snip-

What I might grant you, is the often stated idea that a diode can magically drop 0.6 V in a circuit. What can be missed about this is the fact that the diode will necessarily dissipate heat equal to 0.6 V times the current flowing. The voltage drop is not "magic", it is resistive in nature.

But a diode does act as a resistor: a giant (almost independent from operating point) resistance that impede current flow when reverse biased, and a small (operating point dependent) resistance that let current flow when forward biased. And you confirm it in your last paragraph.

It walks like a duck, it quacks like a duck and it dissipates power like a duck.

[xrunner]

But a diode does act as a resistor: a giant (almost independent from operating point) resistance that impede current flow when reverse biased, and a small (operating point dependent) resistance that let current flow when forward biased. And you confirm it in your last paragraph.

It walks like a duck, it quacks like a duck and it dissipates power like a duck.

Sure you can go that route, but then you render the term "resistor" almost meaningless to anyone.

Some beginner asks Mr. Sredni "What is a resistor?" Smartly he yelps, "Well it's anything at all: an LED, an apple, a quarter, a leaf, a jolly rancher, an ice cube, a cat - oh yea and also those little components with color bands by the way. Just tell those college boys that when they talk about 'em!"

Quack, quack. 

[hans]

I assure you, this is not a troll post.
From the point of view of circuit theory, a diode IS a nonlinear resistor. Period.
You can read, for example, Chua, Desoer and Kuh, "Linear and nonlinear circuits". Top level authors and respected university level textbook.

And an opamp configured in a peculiar way will be a negative resistor.

No its not a resistor. Its just modeled as with a resistive impedance. It "IS" not a resistor, as in the component class, not the modeled properties.

I agree that small signal models will have ''resistors'' pop up everywhere.. transistors, diodes, etc. But those model non-ideal properties (e.g. the channel length modulation of a MOS FET or "output impedance" of a BJT) and are not desired. An ideal diode would have Zd=0 Ohm when Vd>0V and Zd=Inf when Vd<0V

[bdunham7]

I did, in the post you are quoting.
The inability to generalize a concept, namely the concept that resistors are described by voltage-current characteristics that do not need to be linear (nor symmetric).

I think the debate over whether the term "resistor" (when referring to a discrete device) applies only to things that nominally follow Ohms law or applies more generally as you assert is a profoundly uninteresting question.  To me it is like debating whether the term "automobile" applies to pickup trucks.  You may think you know the right answer, but no actual knowledge of the physical universe attaches to these definitions. 

When people talk about the resistance of non-ohmic devices, they can mean either V/I or dV/dI.  And in almost all cases, for example the specified dynamic resistance of a zener diode at various currents, dV/dI is the meaningful number.  Negative resistance is another example, this means that dV/dI is negative, not V/I--unless you are going to expand the definition of "resistor" to include batteries.  Of course, the way you've stated it your definition could include batteries.  If we're going to reclassify electronic components, why not call them all "marklar"?

[switchabl]

I don't consider this to be a mere semantic issue. It is the signal that something is amiss in the educational process.

The diode-resistor issue seems to point to a compartmentalized knowledge problem, where the student is not able to generalize a concept learned in a previous chapter (or course) because nobody has connected the dots for him/her.

I am (mostly) fine with the generalization. In fact it seems I did guess what this was all about after all (if jokingly):

"Aren't all memoryless, time-invariant two-ports just voltage dependent resistors in the end?"
- Gustav Kirchhoff, probably

What is a very bad idea in my opinion is implicitly broadening the meaning of a word. You are effectively redefining the word "resistor" to encompass this generalization. In other words, you now want me to always say "linear resistor" if I want to avoid this new meaning. That can only lead to confusion and debates without substance.

And I might want to generalize the concept along a different axis. After all, in some ways, a resistor has more in common with a capacitor than a diode. They are both linear, passive, time-independent, reciprocal, symmetric. I'll just call it a reactive resistor. Which is really just another kind of resistor, right? Just make sure to call the regular one "resistive resistor" now.
[Yes, that's just a step removed from the idea of a "complex impedance". I think it's a good thing we ended up using a different word for this.]

The original question also suggests that there is such a thing as a "true" definition of a word. You are free to use your own definitions but if you want to communicate with others you have to be explicit about that. And then we can argue whether they are commonly used, useful, confusing, consistent, etc. But to me at least it is not meaningful to ask which one is "the correct one".

[Nominal Animal]

Making a poll about terms without defining those terms is either trolling, or rather stupid.

The entire question is only about one of implicit definitions, and has nothing to do with understanding.  Just replace "an LED" with "a male after surgery", and "a resistor" with "a woman", to see what I mean.

[Sredni]

I am (mostly) fine with the generalization. In fact it seems I did guess what this was all about after all (if jokingly):

"Aren't all memoryless, time-invariant two-ports just voltage dependent resistors in the end?"
- Gustav Kirchhoff, probably

What is a very bad idea in my opinion is implicitly broadening the meaning of a word. You are effectively redefining the word "resistor" to encompass this generalization.

No, why?
A resistor is a device whose state is defined by the current values of voltage and current.
That's it.
It applies to linear resistors, to symmetric nonlinear resistors (incandescent lamps), to asymmetric nonlinear resistors (diodes, LEDs...), etc.

One might use the specifier 'nonlinear' for the diodes, but that does not mean they cease to be resistors; they are just a specific kind of resistor.

Yes, you got it right in your first message.
To my knowledge there are only four types of passive circuital elements: resistors, capacitors, inductors,and memristors. All the rest can be modeled with combinations of these elements, including active devices and circuits.

To avoid making a further post, here is a note from Fluke where they show how to measure the (static) resistance of a diode. It's easy if the forward voltage at the supplied current stays below the compliance of the internal current source.

https://www.fluke.com/en/learn/blog/digital-multimeters/how-to-test-diodes

[SiliconWizard]

Making a poll about terms without defining those terms is either trolling, or rather stupid.

The entire question is only about one of implicit definitions, and has nothing to do with understanding.  Just replace "an LED" with "a male after surgery", and "a resistor" with "a woman", to see what I mean.

Yes.
Beyond the definitions, there's an underlying thought that any model of a reality equates this reality - for which, incidentally, your example also works.

[Sredni]

Making a poll about terms without defining those terms is either trolling, or rather stupid.

Had I defined the terms, there would be no reason for a poll. What I am polling is other people's definition of diode and resistor, so there is no point in suggesting mine (even if I gave it in the ensuing discussion).
Maybe I should rephrase the poll as

Are nonlinear resistors resistors?

Or

Do nonlinear resistors exist at all? And if they do, why can't they have an exponential VI characteristics?

[PlainName]

To avoid making a further post, here is a note from Fluke where they show how to measure the (static) resistance of a diode. It's easy if the forward voltage at the supplied current stays below the compliance of the internal current source.

https://www.fluke.com/en/learn/blog/digital-multimeters/how-to-test-diodes

You are misreading it. They say it's not showing the diode resistance, it is just showing a resistance reading one way and not the other, which you can use to assume the diode is working. Like if you shove a large voltage up a digitial thermometer input it will show a temperature reading. That's not the temperature of whatever is supplying the voltage, it is merely using the temperature reading to indicate a voltage is present.

[Sredni]

It is reading the *static* resistance at the operating point set by the constant current supplied by the DMM.

(It is one value among infinitely many, but it shows that a multimeter can measure the resistance of a diode when used in ohmmeter mode on the device alone).

[switchabl]

What is a very bad idea in my opinion is implicitly broadening the meaning of a word. You are effectively redefining the word "resistor" to encompass this generalization.

No, why?
A resistor is a device whose state is defined by the current values of voltage and current.
That's it.
It applies to linear resistors, to symmetric nonlinear resistors (incandescent lamps), to asymmetric nonlinear resistors (diodes, LEDs...), etc.

Because that is not a common definition in an engineering context where resistor (without further qualification) very strongly implies "ohmic". And this is an EE forum. Theory papers and books sometimes use it as a shorthand for anything that lives in the I-V plane. But they are usually very careful to make that explicit.

[Sredni]

So a nonlinear resistor is NOT a resistor?

[NiHaoMike]

A LED is not a resistor. An incandescent bulb is a resistor, one that emits light and has a rather high temperature coefficient. (So those should be called LERs?)

[amyk]

Since no one has said it yet: yes, it turns into a resistor if you pass enough current through it for long enough.

[bdunham7]

It is reading the *static* resistance at the operating point set by the constant current supplied by the DMM.

(It is one value among infinitely many, but it shows that a multimeter can measure the resistance of a diode when used in ohmmeter mode on the device alone).

Those DMMs that work with a fixed precision test current (which is not all of them b/t/w) are actually displaying the voltage that results from the test current or sometimes a computed ratio of that voltage.  One older model I have specifically refers to diode testing using the 2k resistance range, which uses a 1mA test current and then displays voltage with 2V full scale.  So a typical diode will read like a 600 ohm or so resistor, as you'd expect.  Can I claim that resistors are actually symmetrical linear diodes (diode means two wires, after all) with a highly current-dependent V_f?  Or would that be ridiculous and confusing?

[IanB]

What is a very bad idea in my opinion is implicitly broadening the meaning of a word. You are effectively redefining the word "resistor" to encompass this generalization.

No, why?
A resistor is a device whose state is defined by the current values of voltage and current.
That's it.
It applies to linear resistors, to symmetric nonlinear resistors (incandescent lamps), to asymmetric nonlinear resistors (diodes, LEDs...), etc.

Since at this point you appear to be trolling, let us cut through your trollish behavior.

A resistor is a device with the primary purpose of introducing resistance into a circuit. If that is not its primary purpose, then it is not a resistor, it is something else.

Many devices exhibit resistance, but not all of them are resistors.

If you start calling diodes or other things resistors, then you have made the word "resistor" useless, since that word can no longer be usefully used to identify the things which are sold, labeled, used, and drawn on schematic diagrams as resistors.

[Sredni]

Vf does not exists. It is a figment of our imagination. Plot the exponential characteristic on a logarithmic scale and you will see a straight line. Where is Vf?

But anyway, it's not that nonlinear functions are specializations of linear functions. Among all characteristics in the VI plane, the really special ones are the linear ones - because they allow you to apply superposition. This is why we try to linearize problems wherever we can (small signal analysis, and dynamic resistance which is locally linear).

I have to ask again: is a nonlinear resistor NOT a resistor?

[Sredni]

No, why?
A resistor is a device whose state is defined by the current values of voltage and current.
That's it.
It applies to linear resistors, to symmetric nonlinear resistors (incandescent lamps), to asymmetric nonlinear resistors (diodes, LEDs...), etc.

Since at this point you appear to be trolling, let us cut through your trollish behavior.

Again with this trolling. Did you not see the reference I gave? Leon O. Chua is an authority in the field (I believe he was the one who postulated the existence of the memristor, he's the Chua of Chua's circuit). Both he and Charles A. Desoer taught at MIT. And MIT is the absolute excellence in the EE field. Do you think they are trolls?
Desoer and Kuh also wrote the previous high level bible of circuit theory, used in universities all over the world. No trolling, believe them.

You think that a resistor is defined upon its primary purpose. That's a nice definition for vocational school students. But when you raise the level and want to systematize the resolution of general nonlinear circuits containing any sort of elements you must be a little more cunning. You need to identify the true nature of a component from the point of view of the state variables. And this leads to generalization of concepts. As I said, there are four type of elements: resistors, capacitors, inductors and memristors. A diode? It's a nonlinear resistor. A varicap? It's a nonlinear capacitor. A Josephson junction? It's a nonlinear inductor.
And this is not classification per se: you need to place your elements variables in the correct part of the vector and matrices used to systematically solve these circuits. You don't have slots for diodes, Josephson junctions and so on. You have elements that depends on certain quantities, their derivatives or integrals.

I acknowledge that, so far, the majority of members seem to think that diodes are not resistors, it's fine. I am a bit puzzled by the lack of stance on the existence of nonlinear resistor according to them.

Do nonlinear resistors exists? And why can't they have an exponential VI characteristic?

[bdunham7]

Vf does not exists. It is a figment of our imagination. Plot the exponential characteristic on a logarithmic scale and you will see a straight line. Where is Vf?

Well, that isn't really true in my world(there may be a straight-ish section but not the whole VI plot) but that's beside the point so lets talk about your world.  If you can define 'resistance' as a ratio that changes with applied voltage and/or current and thus can be any number (infinite values, right) and only determined for each individual operating point, then I can claim the same for V_f.  It's not a constant, it just is what it is under any specific condition that one chooses to test it at.  So if I test my newly defined diode (formerly "resistor") with a test current of 1mA and then 2mA, V_f is simply twice as high in the second case.  It has infinite possible values.

[bdunham7]

Do you think they are trolls?

Do nonlinear resistors exists? And why can't they have an exponential VI characteristic?

Nobody is accusing them of being trolls.  Some are accusing you of being a troll.  That's a pretty simple concept and quoting respected authoritative people doesn't change anything either way.

What you are calling a "nonlinear resistor" certainly does exist, but that doesn't mean we have to accept either your terminology or your assertion that failing to acknowledge some theoretical connection between these devices and what is more typically known as a resistor is some big educational failing or lack of understanding.  The definition of a resistor doesn't need to be rigidly defined by a concise theoretical concept either.  Again, if you like, call them all "marklar". 

[magic]

Making a poll about terms without defining those terms is either trolling, or rather stupid.

Considering both the question of the poll and the choices of answers, why not both?

[electrodacus]

Vf does not exists. It is a figment of our imagination. Plot the exponential characteristic on a logarithmic scale and you will see a straight line. Where is Vf?

How do you define an ideal diode?
Also for contrast how do you define an ideal resistor ?

[Sredni]

Vf does not exists. It is a figment of our imagination. Plot the exponential characteristic on a logarithmic scale and you will see a straight line. Where is Vf?

How do you define an ideal diode?
Also for contrast how do you define an ideal resistor ?

My point of view on the non existence of a Vf is summarized here
https://electronics.stackexchange.com/questions/655076/forward-bias-voltage-of-diode/655157#655157

It applies to exponential functions.
An ideal diode has a piecewise vi characteristic that has a definite Vf of zero volts. It's kind of a special case of nonlinear resistor.

[Sredni]

What you are calling a "nonlinear resistor" certainly does exist,

Ok. So if nonlinear resistors do exists and if their vi char can be any (reasonable, non-pathological) function, then we can imagine a nonlinear resistor with exponential characteristic exactly identical to that of a diode.
Is this nonlinear resistor a... resistor?

but that doesn't mean we have to accept either your terminology

I do not ask anyone to accept "my" terminology (again it is not mine), I am just curious to see how this misconception is widespread.

[electrodacus]

Vf does not exists. It is a figment of our imagination. Plot the exponential characteristic on a logarithmic scale and you will see a straight line. Where is Vf?

How do you define an ideal diode?
Also for contrast how do you define an ideal resistor ?

It applies to exponential functions.
An ideal diode has a piecewise vi characteristic that has a definite Vf of zero volts. It's kind of a special case of nonlinear resistor.

I think it will be useful if you can define what an ideal diode is and see if it has anything in common with an ideal resistor.

Let me know of you agree with this ideal diode definition:
Perfect conductor in forward bias and zero volt drop.
Open circuit in reverse bias

An ideal resistor will be defined as purely resistive.

If you agree with this definitions then diodes are clearly not resistors.

[Kim Christensen]

Here I present to you, the "Sredni Common Emitter Amplifier"...

Notice how the voltage divider formed by R1 and R2, sets the base voltage perfectly. These are Blue and Red LEDs respectively. (You may have to stack multiple blue LEDs. This task is left to the students)
R4 (1N4007) and R3 (1N4736) are selected so that Q1 operates in it's linear region and the quiescent voltage at the collector is 1/2Vcc. Input coupling is provided by capacitor C1 and output coupling by C2. There will be some capacitor leakage.

For the students,
Q: If Vcc is 12V and V1 is a perfect 1Vpk-pk sinewave, what is the output waveform's Pk-Pk value and THD?
Bonus Q: model Q1 as an amplifying resistor network. Show your work.

[Sredni]

Kim, do you consider all diodes to be equal? Can you use a tunnel diode where a Schottky diode is needed, or a zener where an LED is required?

I hope not.
Each diode has a specific vi characteristic, just like each linear resistor of different value has one. I consider them all resistors, but I choose them with the right characteristic for their application.

And I am supposed to be the one trolling?
😁

[Kim Christensen]

Kim, do you consider all diodes to be equal? Can you use a tunnel diode where a Schottky diode is needed, or a zener where an LED is required?😁

Those aren't diodes.
They are resistors.

[bdunham7]

Is this nonlinear resistor a... resistor?
I do not ask anyone to accept "my" terminology (again it is not mine), I am just curious to see how this misconception is widespread.

You can call it that if you like.  In the case of an LED, it does 'resist' to a degree so I suppose I can't say it is wrong, just that it is an unusual and unhelpful degeneration of the term 'resistor'.  But what exactly is this 'misconception' that you keep bleating about?  That your 'nonlinear resistor' devices shoud be lumped in with linear ones as kindred spirits and not have a separate category of their own?  Meh.

[DimitriP]

TL;DR
...but this has a smell of an upcoming veritasium video.

I am a resistor of most things "rather stupid".
We should all be resistors.

[IanB]

It's mainly a problem of language and logic.

Properties of circuit elements include resistance, capacitance and inductance.

All resistors have resistance. Not all devices with resistance are resistors.

All capacitors have capacitance. Not all devices with capacitance are capacitors.

All inductors have inductance. Not all devices with inductance are inductors.

If the topic title were changed to something like "Do LEDs exhibit resistance to electric current?" then the whole thread would not exist.

[SiliconWizard]

Yes, but as I said earlier, that may just be a rhetorical question involving modeling components.

Can a diode be mathematically modeled with a variable resistor, the resistance of which is a non-linear function of voltage? For a simplified model, yes. Does that make it a resistor?

From the usual definition, no, as Ohm's law defines a resistor as a constant relationship between voltage and current. It can't vary, linearly or non-linearly. Now, real resistors have a resistance which does vary, at least with temperature (and thus, with current, due to damn Joules).

Models.

[magic]

Nah, it's another common and utterly boring case of somebody learning about resistors and insisting that everything that passively resists current flow must be a resistor, on purely linguistic grounds.

The OP hasn't posted any single mathematical model of anything.

edit
Except for the idea that you can define "momentary resistance" of a diode as the ratio of its momentary Vf and If, which is an utterly useless notion and I'm pretty sure it is not the topic of any reputable sources that the OP might bring up to justify himself.

[switchabl]

So a nonlinear resistor is NOT a resistor?

In an ordinary (non network theory) sense, no. Blame it on the theorists who couldn't be bothered to come up with a new name for their extended concept. The physical component and it's idealized (linear) version definitely came first. And nobody wants to keep specifying "linear resistor" when that's what they mean 99% of the time.

Vf does not exists. It is a figment of our imagination. Plot the exponential characteristic on a logarithmic scale and you will see a straight line. Where is Vf?

Vf exists in an approximate sense because there is a limited useful current range between "does not visibly light up" and "catches fire". As a consequence of the exponential characteristic, the voltage does not actually vary that much throughout this range. For design work you would usually start there, then check the actual I-V curve or do a simulation later if you need something more accurate.

Except for the idea that you can define "momentary resistance" of a diode as the ratio of its momentary Vf and If, which is an utterly useless notion and I'm pretty sure it is not the topic of any reputable sources that the OP might bring up to justify himself.

It is unfortunately a thing in (non-linear) network theory to call everything a "resistor" that can be defined in terms of f(v, i, t) = 0. A regular resistor would actually be a "linear, time-invariant resistor" in that terminology. I have never before met anyone who tried to push that definition in engineering.

It's a bit like going on a computer graphics forum, showing a picture of a circle and asking people if it's "not a sphere, because it's a circle" or "just a different kind of sphere". Indeed, in mathematics the word "sphere" is usually generalized to include "spheres" of arbitrary dimensionality of which both the circle (the 1-sphere) and the actual sphere (the 2-sphere) are just special cases. And you can find many reputable sources which will back this up. But that doesn't make more appropriate or less confusing in a different context.

[tom66]

Yes.

But only when you burn it out and resistance approaches zero.  That makes it a Darkness Emitting Diode (DED).

[Zero999]

I wonder how many people here chose electronics to avoid philosophy?

This discussion is no longer about engineering or science. We might as well talk about fascism, Marxism, feminism, gender ideology, critical race theory etc. 

At this point, discussing critical social justice seems far more productive.

Let's start by looking at systemic racism and patriarchal influence in engineering. The fact that the colours brown and black in the resistor colour code indicate low values 0 and 1 and white is the highest at 9, demonstrates that resistors are racist and white supremacist. Male and female connectors are a sign of heteronormativity, which marginalizes gay and non-binary voices. 

[tom66]

OK, this thread has officially jumped the shark with that post.   

[Berni]

Anything can be a resistor if you want it to look like a resistor.

Inductors have internal resistance so at DC they are low value resistors.
Capacitors have leakage current so at DC they are a high value resistor.
Memrisors are also just a resistor if you apply DC across it.
Heck even a mono audio jack can be a resistor since the insulating materials inside it have a very very high but not quite infinite resistance.
Or even all 2 terminal devices could be considered resistors since they can have a voltage U and current I across it so you can apply ohms law.

The question is more "is it appropriate to think of it as a resistor?"

In some cases it definitely is appropriate to think of a diode as a resistor. For example if you are analyzing the feedback loop of a LED or laser diode driver or something you will be interested in the didoes dynamic resistance, since it is what affects the loop gain and might decide if your loop is stable or not.

But in the vast majority of cases it is better to consider the diode being well.. a diode.Especially in simple calculations like calculating the correct resistor for a LED. It is definitely not appropriate to wave this idea around in an educational setting as this would only serve to confuse people into thinking they can use a diode as a resistor in a circuit. After all what datasheet specifies the characteristic in Ohms? They all show the IV curves instead, those make more sense.

Imagine the diode as whatever helps you get the job done. Just don't expect others to imagine it the same way because they might be doing the same job with that diode

[Siwastaja]

I can even show my hand: it is a resistor, a nonlinear resistor to be precise. Why? because its state is determined by the present values of voltage and current (and not their derivatives and integrals like capacitors, inductors, and memristors).
...
But a lot of people have trouble in recognizing that.
...
I just wanted to see how widespread this misconception is.

A very INTERESTING and internally coherent and logical way to define a resistor, but you can't just arbitrarily come up with new meanings for existing words and then say others have "trouble" recognizing your invention, or call this misconception.

There is a simple solution to all of this: just call an LED LED. Then anyone can check out the characteristics, such as voltage-current transfer curve, amount of capacitance and inductance, from the literature, or, more exactly, from a particular datasheet. This is to avoid obfuscation and word trickery.

[Sredni]

So, it seems that the main objection comes down to:

Since Ohm's law is defined as a linear relationship, nonlinear *resistors* are not resistors.

Fascinating.

[langwadt]

So, it seems that the main objection comes down to:

Since Ohm's law is defined as a linear relationship, nonlinear *resistors* are not resistors.

Fascinating.

if you see everything you can stick the probes of an ohmmeter on and get a result as a resistor then everything is a resistor, making the word pointless

[Rick Law]

I can even show my hand: it is a resistor, a nonlinear resistor to be precise. Why? because its state is determined by the present values of voltage and current (and not their derivatives and integrals like capacitors, inductors, and memristors).
...
But a lot of people have trouble in recognizing that.
...
I just wanted to see how widespread this misconception is.

A very INTERESTING and internally coherent and logical way to define a resistor, but you can't just arbitrarily come up with new meanings for existing words and then say others have "trouble" recognizing your invention, or call this misconception.

There is a simple solution to all of this: just call an LED LED. Then anyone can check out the characteristics, such as voltage-current transfer curve, amount of capacitance and inductance, from the literature, or, more exactly, from a particular datasheet. This is to avoid obfuscation and word trickery.

Adding to Siwastaja's point:  When one can (re)define resistor that way, then everything on earth is a resistor.  You sure can call "Air" a resistor, just give it enough voltage, we see thunder lightning.

Current flow is a matter of electrons transfer.  We all know that electrons can go anywhere physical condition dictates, even in vacuum.  I am hard pressed to think of any material that entirely block the transfer of electrons from point A to point B in this universe we know. 

I personally think, best definition for resistor is "Something design to pass a specific amount of current directly proportional to the voltage applied (ohm's law)."

[Nominal Animal]

When no specific context or definition is supplied, one should default to the dictionary meaning for maximum chance of successful communication.  Otherwise, it is almost certain that the discussion will be about the definition or context, and thus superficial; never reaching the actual interesting stuff.  It is like arguing about when to argue about a practical thing, instead of arguing about the practical thing directly.

For a resistor, this is "an electric component that transmits current in direct proportion to the voltage across it" (Wiktionary); "a part of an electrical circuit designed to produce a particular amount of resistance to the flow of current" (Cambridge dictionary); "electrical component that opposes the flow of either direct or alternating current, [...] Resistors can have a fixed value of resistance, or they can be made variable or adjustable within a certain range, in which case they may be called rheostats, or potentiometers." (Britannica).

In other words, by default, when one uses "resistor" without a specific context or definition, it refers to a circuit element with fixed resistance, and thus a linear relationship (direct proportion) between voltage and current over it.

None of this is about electrical engineering per se; this is purely about how to communicate with others effectively.  If you disagree, you're basically offering your own theory about effective communication between humans, so you better have a ton of proof about your assertions.  A couple of eminent scientists or half-nut Nobel laureates is not enough; they are so focused on their own area of expertise that their opinions about human communications are basically irrelevant.  (In mathematics, physics, et cetera, this is amply evidenced by these scientists often developing their own notations, because they fail to convey the concepts effectively using existing notations.)

Now, if one bothers to additionally compare the dictionary references to "nonlinear resistors", one will see that terms "nonlinear element" or "nonlinear component" are preferred and more widely used; see for example Wikipedia, Britannica/memristor, and so on.

Considering all of the above:

I for one fully reject the term "nonlinear resistor", and insist you use the standard term, "nonlinear element" or "nonlinear component" instead.

If we were to accept such twisted terms, we should accept "enhanced bicycle" for an automobile, "wide-ended stick" for a shovel, "multi-prong spoon" for a fork, and so on.  Such terms reduce the likelihood of concepts being conveyed without degradation, without bringing anything positive to the discussion; only allowing semantic games and trickery, which leads to discussions where nobody learns anything new.  Therefore, such twisted terms should be rejected with maximum prejudice.

[Sredni]

Anything can be a resistor if you want it to look like a resistor.

As I said before, I am neglecting secondary or parasitic effects.
A resistor is a device that primarily behaves as a resistor. Yes, it may have some parasitic capacitance and inductance but these are minor effects unless you push the conditions too far.
A piece of coiled wire is a shunt resistor until I push the frequency so high that its inductive reactance becomes appreciable. And if I push it even further it might even show a significant capacitive reactance.

But I made clear that I am neglecting secondary effect. I am here talking about a diode completely described by it exponential Shockley equation. That is, soleley by its V-I relationship. I am even neglecting the effect of junction capacitance (which is there) because unless I push the frequency too far (or build a diode with abnormous junction capacitance to exploit that effect), its effect in the qV plane is negligible compared to the *resistive* behavior in the VI plane.

And what a diode with negligible capacitance does is... showing a resistance (which is not constant but depends on the voltage or current). That is all it does, from the point of view of the circuit. It does not matter that the power it takes out goes all in IR heat, visible light or aura vibrations. The circuit sees a variable resistance (a fixed resistance once you fixed the operating point).

And yet people cannot see it is behaving as a resistor. I find it fascinating. (I have just watched an old ST convention on YT so I'm in Spock mode, now).


(Funny that nobody has noticed I called a varicap a nonlinear capacitor...)

[MK14]

(Bold and font size change, made by me)

And what a diode with negligible capacitance does is... showing a resistance (which is not constant but depends on the voltage or current). That is all it does, from the point of view of the circuit. It does not matter that the power it takes out goes all in IR heat, visible light or aura vibrations. The circuit sees a variable resistance (a fixed resistance once you fixed the operating point).

And yet people cannot see it is behaving as a resistor. I find it fascinating. (I have just watched an old ST convention on YT so I'm in Spock mode, now).

But, it is NOT behaving like a resistor (the diode), because it reacts in completely different ways (i.e. current flow or not), depending on the polarity across it (unlike a proper resistor, which is unpolarised).  I.e. reversing the polarity, will usually have a dramatic effect on the current flow.

Also, the current verses the voltage across it (non-ohmic), is usually not proportional, in the same way it would be with a real resistor.

Example:
To run down a battery, overnight.  If I gave you a small, brand new 9 volt battery, and a power diode.  Then, as a challenge, you needed to connect it up and leave it over-night.  Assuming I've rubbed off the polarity markings on the diode.  How would you be more than 50% sure, that you had connected it up the right way, to discharge the battery (assuming I don't give you enough time, to see if it or the battery, gets hot or not), overnight?

N.B. The DIFFERENCE matters.  Because that is why a diode is called a diode and not a fuse, short-circuit, open-circuit or resistor etc.

[Sredni]

It is not behaving like a *linear* resistor. It has an asymmetric nonlinear vi characteristic. As I said, the amount of resistance depends on the operating point, but it is resistance nonetheless.

I mean, it is not capacitance. Not inductance. Not memristance.
I don't think it diodance...

Now I am curious: are nonlinear inductors... Inductors?
If I take a coil in air with linear relationship phi = L I, that is an inductor, will it cease to be an inductor when I stick a piece of iron inside it making its characteristic in the phi-I plane nonlinear?

[MK14]

It is not behaving like a *linear* resistor. It has an asymmetric nonlinear vi characteristic. As I said, the amount of resistance depends on the operating point, but it is resistance nonetheless.

I mean, it is not capacitance. Not inductance. Not memristance.
I don't think it diodance...

Now I am curious: are nonlinear inductors... Inductors?
If I take a coil in air with linear relationship phi = L I, that is an inductor, will it cease to be an inductor when I stick a piece of iron inside it making its characteristic in the phi-I plane nonlinear?

A 'resistor' is normally taken, to mean a specific physical entity (component), that often has two (or more, e.g. four) terminals/leads/connections, and a (usually) somewhat precise value and other (datasheet) characteristics, such as specific dimensions, and maximum ratings.

[Kim Christensen]

We name things by their dominant property.
That's why we do not call diodes, capacitors, and inductors, resistors.   

[IanB]

but it is resistance nonetheless

Ah, you are starting to improve your English. If you change the verb and say that a diode "has resistance", then you will be doing even better.

[switchabl]

This thread has reminded me of a delightful little story I read a long time ago and it was a nice surprise to find that someone has translated it into English: A Table is a Table

[M0HZH]

Anything can be a resistor in very specific circumstances.

Nothing is a resistor if you use too much voltage.

For everything else, we use the most dominant caracteristic.

[Sredni]

We name things by their dominant property.
That's why we do not call diodes, capacitors, and inductors, resistors.   

The property being...?

Diodance?

[electrodacus]

As I said before, I am neglecting secondary or parasitic effects.

That is not a true statement else there will be no discussion here.


I asked you to define an ideal diode as that will have no resistance at all.
Above image shows a simple equivalent model of a real diode. If that resistor is non linear as most resistors are it has nothing to do with the diode (theoretical ideal diode).
If you say a diode is nothing other than a resistor you should be able to remove that "ideal diode" from the model.

[Kim Christensen]

We name things by their dominant property.
That's why we do not call diodes, capacitors, and inductors, resistors.   

The property being...?
Diodance?

Close. It's called rectification. Diodes are also called rectifiers. That's it's dominant property and one of it's main use cases. Hence we don't call them resistors.
 

[bdunham7]

The property being...?

Diodance?

No, "nonlinear resistance" is just fine if you insist on assigning a specific term to its properties.  That doesn't mean we need to call it a resistor anymore than the fact that I can locomote makes me a locomotive.

[Sredni]

I don't know how to say it more clearly. An ideal diode is a nonlinear resistor whose vi characteristic is a piecewise function formed by an horizontal line until V=0 and a vertical line for V=0.
It is a resistor that has infinite resistance (the horizontal part of the vi char) for V<0 and zero resistance for V>=0.
I am using resistance to specify its behaviour.

The device you show is a nonlinear resistor with piecewise linear VI characteristic that shows infinite resistance for V<Vf and a resistance that depends linearly from the operating point for V>Vf.

A silicon diode is a nonlinear resistor with exponential continuous VI characteristic. It shows very high resistance for negative voltages and an increasingly  smaller (operating point dependent) resistance for positive voltages.

It is always about the resistance it opposes to the flow of current.

[Sredni]

We name things by their dominant property.
That's why we do not call diodes, capacitors, and inductors, resistors.   

The property being...?
Diodance?

Close. It's called rectification. Diodes are also called rectifiers. That's it's dominant property and one of it's main use cases. Hence we don't call them resistors.

What are the physical units of this "rectification"?

I use resistance and it is expressed in ohms. I can tell you exactly how many ohms a silicon diode 1N4148 exhibits at a given voltage or current.

I should remind you that in circuit theory there are only four types of (passive) elements, each one described quantitatively by their respective property:

1. Resistance
2. Capacitance
3. Inductance
4. Memristance

Do you think there is a fifth one, rectification or rectificance?

[MK14]

What are the physical units of this "rectification"?

I use resistance and it is expressed in ohms. I can tell you exactly how many ohms a silicon diode 1N4148 exhibits at a given voltage or current.

I should remind you that in circuit theory there are only four types of (passive) elements, each one described quantitatively by their respective property:

1. Resistance
2. Capacitance
3. Inductance
4. Memristance

Do you think there is a fifth one, rectification or rectificance?

What exactly is your equivalent circuit for a diode (such as the 1N4148, you mentioned)?

Let's put it in a black box, and let an independent observer, see if they can tell your equivalent circuit, from another black box, containing a real diode.

Inspiration for this post, came from here:
https://www.sciencedirect.com/topics/engineering/circuit-theory

[PlainName]

I don't know how to say it more clearly.

I think if you look just two message up your problem will be solved.

[madires]

As an academic exercise one could model an LED as a strange kind of resistor. But there's more. An LED can be used as a poor light sensor. So one could have the idea to model an LED as a current or voltage source. And we could model a power source as a negative resistance. Now the LED's resistance model becomes even more complex. But does this make an LED a power source, a resistor, or something else?

[Berni]

And what a diode with negligible capacitance does is... showing a resistance (which is not constant but depends on the voltage or current). That is all it does, from the point of view of the circuit. It does not matter that the power it takes out goes all in IR heat, visible light or aura vibrations. The circuit sees a variable resistance (a fixed resistance once you fixed the operating point).

And yet people cannot see it is behaving as a resistor. I find it fascinating. (I have just watched an old ST convention on YT so I'm in Spock mode, now).

(Funny that nobody has noticed I called a varicap a nonlinear capacitor...)

The problem is that you are just mixing together commonly used terms as if it was one thing. There is a reason why these things are called different things.

What you are trying to say is that a diode exhibits the effect of "electrical resistance" or "resistivity".

This effect is not particularly special and just describes that the device can consume electrical power and turn it into something else, rather than store it and give it back(like capacitance or inductance can). The most common example of this is indeed a resistor that turns the applied power into heat, but other devices can turn it into other things, like a LED can turn it straight into light, an electrolysis cell can turn it into chemical energy..etc. The laws of physics impose this as a requirement since energy can only be moved or converted. This is why the effect of resistivity is everywhere in electrical circuits. Any DC circuit can only be comprised of power sources and resistances to extract work from said sources (Yes even a memristor becomes just a regular resistor once observed in steady state DC conditions). This in itself is pretty neat.

A resistor is 2 terminal electrical device that primarily exhibits the effect of electrical resistance. From wikipedia the first line reads "A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element" Such components are expected to have predictable and well controlled resistance, since the ones that don't are given different names, this is to distinguish them and avoid confusion. For example a resistor where its resistance is strongly affected by the voltage across it is called a varistor or "voltage dependent resistor". So if you are to draw similarities, you can say a diode is a form of asymmetrical varistor.

In a similar vein a varicap diode is still just a PN junction diode. It has the same type of "varistor like" behavior as a regular rectifier diode. So why does it need a different name then? It is just because it is specifically optimized to implement the effect voltage dependent capacitance, so the name already tells you about what characteristics to expect from the component.

But bending the meaning of common industry standard terms helps nobody. It just causes confusion and misunderstanding.

[magic]

An ideal diode is a nonlinear resistor whose vi characteristic is a piecewise function formed by an horizontal line until V=0 and a vertical line for V=0.
It is a resistor that has infinite resistance (the horizontal part of the vi char) for V<0 and zero resistance for V>=0.

If only William Shockley could realize it's that simple and spare us those bizarre exponential equations...

[Gyro]

It's quicker to draw the schematic, but specifying some of the values is very tricky (and sample dependent) and the parasitics are absolutely horrendous.  

[Zero999]

We name things by their dominant property.
That's why we do not call diodes, capacitors, and inductors, resistors.   

The property being...?
Diodance?

Close. It's called rectification. Diodes are also called rectifiers. That's it's dominant property and one of it's main use cases. Hence we don't call them resistors.

What are the physical units of this "rectification"?

I use resistance and it is expressed in ohms. I can tell you exactly how many ohms a silicon diode 1N4148 exhibits at a given voltage or current.

I should remind you that in circuit theory there are only four types of (passive) elements, each one described quantitatively by their respective property:

1. Resistance
2. Capacitance
3. Inductance
4. Memristance

Do you think there is a fifth one, rectification or rectificance?

EDIT:

To spell it out for you:

A diode is not a passive device.

[Nominal Animal]

I can buy LEDs and resistors (of the fixed resistance kind) off Mouser, but nobody sells any "nonlinear resistors".  Are they magick?

Or is it just a stupid term used in a narrow field, because the more widely used "nonlinear component" or "nonlinear part" just didn't sit right with The Big Names?  Just like the artsy-fartsy visual arts people who redefine exact physics terms all willy-nilly, and then wonder why they find physics so unfathomably strange (until they learn that terms are specific to the field or context they are used in, and not universal).

If you want to use the narrow field definition, say so; otherwise you're just playing tricks on others.

It is okay to use field specific terms only when you make the usage clear; i.e. either define the term, for example via "(according to the definition used in electrical engineering)" or "(according to the definition used in visual arts)".  Otherwise everyone else will default to the standard dictionary definition, and think of you as a highly obnoxious person for playing word games on others like that.

The fact that Sredni acknowledged that had they defined the terms there would be no reason for the poll, tells everyone everything worth knowing.  The reason this poll was created has nothing to do with the terms or devices described by those terms, and everything to do with Sredni trying to feel superior to others by playing word games.

I find it contemptible.  It does not surprise me at all that the question initially came up in StackExchange: a site for social points-scoring masquerading as questions and answers. 

[tooki]

Let's start by looking at systemic racism and patriarchal influence in engineering. The fact that the colours brown and black in the resistor colour code indicate low values 0 and 1 and white is the highest at 9, demonstrates that resistors are racist and white supremacist. Male and female connectors are a sign of heteronormativity, which marginalizes gay and non-binary voices.

You’re right! As a gay man, I shall endeavor to only use hermaphroditic connectors in my future designs! (Since then each contact is the same as the one it mates with. Like me! 😂)

[Gyro]

Let's start by looking at systemic racism and patriarchal influence in engineering. The fact that the colours brown and black in the resistor colour code indicate low values 0 and 1 and white is the highest at 9, demonstrates that resistors are racist and white supremacist. Male and female connectors are a sign of heteronormativity, which marginalizes gay and non-binary voices.

I sense an opportunity to bring this daft thread to a close.

[Sredni]

I sense an opportunity to bring this daft thread to a close.

It looks like some people feels threatened by ideas that do not fit in the frozen model they have made of the world when they were in high school.
I have witnessed a lot of name calling in this thread, and I have chosen not to respond to any provocation (stupid idea, daft thread, silly jokes about using resistors symbols everywhere, complex of superiority...). It seems we have reached a new level: since I do not accept provocations, the reason for closing the thread is fabricated entirely by someone else.

This is interesting from a social point of view, but I intend to keep the thread firmly on technical grounds and I hope that an evential moderation would be limited to the removal of the non technical posts.

[Nominal Animal]

It looks like some people feels threatened

No, nobody is threatened by your lame attempt at tricking others so you can feel superior.  We're just exasperated.

Perhaps you should read the Why writing style and grammar matters in posts, a sticky in the Beginners forum?  Especially the paragraph about terms and abbreviations,

Because terms and abbreviations vary across the world, it is important to define the terms and abbreviations you use, to ensure your post is understood the way you intended.  For example, CIA does not always refer to an intelligence agency.  It may refer to a MOS 6526 or MOS 8520 Complex Interface Adapter IC (as used with the 6502 microprocessor), "Confidentiality, Integrity, Availability" (concept triplet in information security), CAN in automation, or a number of other things including four different international airports.  It also means that arguments like what a term exactly means (its definition) are useless, because it is just a matter of convention, and we can agree to one definition in one thread, and a different one in another thread; the important thing is that we all understand the posts the same way.

[DimitriP]

I sense an opportunity to bring this daft thread to a close.

About ^%^ time!!

[TimFox]

There is a standard term for a two-terminal device with an arbitrary relationship between the voltage and current across and through the terminals:
"One-Port" see  https://en.wikibooks.org/wiki/Circuit_Theory/One_Port_Devices 
In general, what's inside the rectangle that comprises the one-port is a bunch of more elementary devices, such as resistors, capacitors, diodes, etc., defined in a civilized manner and connected in a more-or-less complex circuit.
There's no need to re-name the one-port the "resistor", since we already have a good definition for a resistor that is far less general than what can be called a one-port.

[Sredni]

The problem is that you are just mixing together commonly used terms as if it was one thing. There is a reason why these things are called different things.

When I attended elementary school, when the dinosaurs roamed the world,  they taught me about sets. Do they still teach sets nowadays?

Because (here < stands for "include", and U stands for "union"):

Resistor < Linear resistor U Nonlinear resistor
Nonlinear resistor < incandescent lamps U diodes U ...

So, you can still call it a diode, recognize that it is a nonlinear resistor and, as such, that it belongs to the more general set of resistors.

Does this make any sense to you?

What you are trying to say is that a diode exhibits the effect of "electrical resistance" or "resistivity".

This effect is not particularly special and just describes that the device can consume electrical power and turn it into something else,

The point I make is that this is ALL a diode does.
Huge resistance when reverse biased, small resistance when forward biased. This is not a side effect. It is what it does (if we neglect secondary effects due to parasitics in real devices).
It does not store energy in the electric field.
It does not store energy in the magnetic field.
It does not do whatever sorcery a memristor does.
It just oppose a resistance that takes power out of the circuit.
 

[MK14]

The problem is that you are just mixing together commonly used terms as if it was one thing. There is a reason why these things are called different things.

When I attended elementary school, when the dinosaurs roamed the world,  they taught me about sets. Do they still teach sets nowadays?

Because (here < stands for "include", and U stands for "union"):

Resistor < Linear resistor U Nonlinear resistor
Nonlinear resistor < incandescent lamps U diodes U ...

So, you can still call it a diode, recognize that it is a nonlinear resistor and, as such, that it belongs to the more general set of resistors.

Does this make any sense to you?

What you are trying to say is that a diode exhibits the effect of "electrical resistance" or "resistivity".

This effect is not particularly special and just describes that the device can consume electrical power and turn it into something else,

The point I make is that this is ALL a diode does.
Huge resistance when reverse biased, small resistance when forward biased. This is not a side effect. It is what it does (if we neglect secondary effects due to parasitics in real devices).
It does not store energy in the electric field.
It does not store energy in the magnetic field.
It does not do whatever sorcery a memristor does.
It just oppose a resistance that takes power out of the circuit.

No, this seems to be heading into the ...
All cars are vehicles.
BUT, not all vehicles are cars.
Type of argument.

Or to use your terminology (Analogy):

Cars < Real-Cars U Toy-Cars U Pictures-of-Cars

Therefore (using your apparent logic), a toy car, is a member of 'Cars', but it is NOT, as you can't drive a toy car, between different towns etc.

A picture of a car, has some kind of connection, to a real car.  But should not be considered, as a real or usable car.  Similarly, LEDs are NOT suited to be used or classed as resistors.

Or get LEDs in a range of Ohm values between a fraction of an Ohm and many tens of megaohms.

I.e. LEDs are not usually used (or suitable for being used) as 'RESISTORS'.

[IanB]

It looks like some people feels threatened by ideas that do not fit in the frozen model they have made of the world when they were in high school.

It often turns out that when someone thinks they are smarter than everyone around them, that he or she is in fact the dumb one, and everyone around them is just raising their eyes to the heavens in amusement.

[Sredni]

It looks like some people feels threatened by ideas that do not fit in the frozen model they have made of the world when they were in high school.

It often turns out that when someone thinks they are smarter than everyone around them, that he or she is in fact the dumb one, and everyone around them is just raising their eyes to the heavens in amusement.

Anyone has the email of Leon O. Chua?

[DimitriP]

I find it contemptible.  It does not surprise me at all that the question initially came up in StackExchange:

When the fiirst post contains the phrase ""another forum" it's never a good sign.

[Sredni]

There is a standard term for a two-terminal device with an arbitrary relationship between the voltage and current across and through the terminals:
"One-Port" see  https://en.wikibooks.org/wiki/Circuit_Theory/One_Port_Devices 
In general, what's inside the rectangle that comprises the one-port is a bunch of more elementary devices, such as resistors, capacitors, diodes, etc., defined in a civilized manner and connected in a more-or-less complex circuit.
There's no need to re-name the one-port the "resistor", since we already have a good definition for a resistor that is far less general than what can be called a one-port.

Ok, so you too think that there are no nonlinear resistors. They are just one-ports. In my view, using set theory

One port < Resistor U Capacitor U Inductor U Memristor U Any circuits composed of the connection of the previous four

And then I specialize each sunset into linear and nonlinear. So to me (and to Chua, Desoer and Kuh) nonlinear resistors are a specialization of one ports, like linear resistors from which they are disjoint.

But let's switch for a second to inductors: what do you call a coil with a ferrite core? A one port (but not an inductor)? Because I guess inductor only means linear inductor, right?

[globoy]

Sredni, to answer your original question.  No, I don't think of a LED as a resistor.  Even if I accept your premise that in some abstract theoretical sense it might be considered one.  Why would I?  What useful purpose does doing so achieve?  Is it going to help me the next time I design a circuit that includes a LED?  If so, how?

And finally, why do you ask this?  To what end is your question?

[TimFox]

There is a standard term for a two-terminal device with an arbitrary relationship between the voltage and current across and through the terminals:
"One-Port" see  https://en.wikibooks.org/wiki/Circuit_Theory/One_Port_Devices 
In general, what's inside the rectangle that comprises the one-port is a bunch of more elementary devices, such as resistors, capacitors, diodes, etc., defined in a civilized manner and connected in a more-or-less complex circuit.
There's no need to re-name the one-port the "resistor", since we already have a good definition for a resistor that is far less general than what can be called a one-port.

Ok, so you too think that there are no nonlinear resistors. They are just one-ports. In my view, using set theory

One port < Resistor U Capacitor U Inductor U Memristor U Any circuits composed of the connection of the previous four

And then I specialize each sunset into linear and nonlinear. So to me (and to Chua, Desoer and Kuh) nonlinear resistors are a specialization of one ports, like linear resistors from which they are disjoint.

But let's switch for a second to inductors: what do you call a coil with a ferrite core? A one port (but not an inductor)? Because I guess inductor only means linear inductor, right?

I call it a non-linear coil.  Under reasonable limited conditions, it exhibits inductance.  In Spice, it can be modeled as a one-port that includes hysteresis.
Of course there are one-ports, encased in plastic, that can be characterized as non-linear resistors (with non-linear V vs. I equations), but extending that nomenclature to semiconductor devices is useless sophistry.

[Kim Christensen]

It is always about the resistance it opposes to the flow of current.

Yes... But it's still called a diode. I don't know how I can say that more clearly.

[switchabl]

I don't think there is anything more I can (or want) to say on the semantics argument. I just want to add one word of caution for anyone thinking of adopting the kind of mental model the OP is proposing:

There is nothing wrong mathematically with thinking of an (idealized) diode as a circuit element that has varying resistance depending on the terminal voltage. But it is important to keep in mind that a physical diode is nothing like that. It is not made from some bulk material with variable resistance, it is a semiconductor junction. Otherwise your intuition can quickly lead you astray. To give just one example, a resistor exhibits thermal noise with a spectral density of <i²> = 4k_BT/R whereas the (primary) noise mechanism in a diode is shot noise with <i²> = 2eI.

[Sredni]

Ok, so you too think that there are no nonlinear resistors. They are just one-ports. In my view, using set theory

One port < Resistor U Capacitor U Inductor U Memristor U Any circuits composed of the connection of the previous four

And then I specialize each sunset into linear and nonlinear. So to me (and to Chua, Desoer and Kuh) nonlinear resistors are a specialization of one ports, like linear resistors from which they are disjoint.

But let's switch for a second to inductors: what do you call a coil with a ferrite core? A one port (but not an inductor)? Because I guess inductor only means linear inductor, right?

I call it a non-linear coil.  Under reasonable limited conditions, it exhibits inductance.  In Spice, it can be modeled as a one-port that includes hysteresis.
Of course there are one-ports, encased in plastic, that can be characterized as non-linear resistors (with non-linear V vs. I equations), but extending that nomenclature to semiconductor devices is useless sophistry.

Ok, therefore the big toroidal core coils used in switched power supplies are not inductors, but something different called nonlinear coil. Are we clear on that?
Can we also say that all inductors in a SEPIC are
 linear? What does the I stand for in the acronym?

[TimFox]

Yes, the “big toroidal core coils” (your phrase) have inductance.
They also have resistance.
Therefore you (but not I) can call them “resistors” and confuse them with RN65D metal-film thingies.

[Sredni]

As I have already explained at least three times, I am neglecting secondary effects. The ESR of a coil is a side effect. (While the static resistance exhibited by a diode is the main effect).

A 300uH coil to me is an inductor, irregardless of the fact that it be wound around a ferrite core or not. If it is nonlinear and shows saturation and hysterisis it is a nonlinear inductor and as such, it still belongs to the broader category of Inductors, side by side with the linear inductors.

While for people who do not believe in the existence on nonlinear inductors, it is a nonlinear coil (NLC, in brief). Like those used in SEPNLCC circuits.

[TimFox]

Enough nonsense—back to the original question.
I have two similar-size cylinders with axial leads.
One is an RN65D metal-film resistor.
Testing it, I see that it obeys Ohm’s law quite well, but has small parasitic inductance and capacitance, along with a slight self-heating and temperature co-efficient.
Ignoring the minor deviations from the Platonic ideal, I confirm the common opinion that it be called “resistor”.
The other is labeled 1N4007.
Initial measurements show it is not close to Ohmic, especially with respect to polarity reversal.
Testing it, I see that it conforms well to Shockley’s equation for a semiconductor diode (including temperature effects) with small parasitic series resistance (in the package), along with non-linear junction capacitance and charge storage.
Again, following your advice to ignore secondary effects, I confirm its proper name as “diode”.
Calling it a “resistor” would only be confusing.

[Kim Christensen]

What are the physical units of this "rectification"?
I use resistance and it is expressed in ohms. I can tell you exactly how many ohms a silicon diode 1N4148 exhibits at a given voltage or current.

[Sredni]

Enough nonsense—back to the original question.
I have two similar-size cylinders with axial leads.
One is an RN65D metal-film resistor.
Testing it, I see that it obeys Ohm’s law quite well, but has small parasitic inductance and capacitance, along with a slight self-heating and temperature co-efficient.
Ignoring the minor deviations from the Platonic ideal, I confirm the common opinion that it be called “resistor”.
The other is labeled 1N4007.
Initial measurements show it is not close to Ohmic, especially with respect to polarity reversal.
Testing it, I see that it conforms well to Shockley’s equation for a semiconductor diode (including temperature effects) with small parasitic series resistance (in the package), along with non-linear junction capacitance and charge storage.
Again, following your advice to ignore secondary effects, I confirm its proper name as “diode”.
Calling it a “resistor” would only be confusing.

Ok, this is the VI characteristic of a 1N4148 diode in LTSpice (default temperature) - sorry I went on simulating and picked 1n4148 instead of 1n4007. But it's immaterial.



and this is the resistance offered by the diode as a function of the voltage across it



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



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.



Now, let's see if we can make something with these values...
Let's say I have a 5V supply and a diode that has exactly that characteristic (you can find yours experimentally at your lab temp).
If the diode at 5mA shows a resistance of 132 ohms, we can create a circuit that drives 5mA by using a resistor such as

5mA (Rx + Rdiode) = 5V

or Rx = 5V / 5mA - 132 = 1000 - 132 = 868 ohm

Oh, look: 660 mV voltage, 5 mA current. What a lucky break.



How about the other one?

The diode shows 23.2 kohm at 0.4V.

Let's change equation, since I did not record the current. Let's use a voltage divider equation

Rdiode/ (Rx + Rdiode) 5V = 0.4V

23.2k / (Rx + 23.2k) = 0.4 / 5

Rx = 23.2k 5 / 0.4 - 23.2k = 266.8 kohm

and, oh look:



0.4V.
Now, let's see what we can do with resistors:



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?

[schmitt trigger]

I sense an opportunity to bring this daft thread to a close.

I believe the thread is rapidly approaching the 200 post milestone.

[Sredni]

What exactly is your equivalent circuit for a diode (such as the 1N4148, you mentioned)?

Let's put it in a black box, and let an independent observer, see if they can tell your equivalent circuit, from another black box, containing a real diode.

There is no need for an equivalent circuit: you specify the VI characteristic. Then if you want you can use other elements to approximate it, but it's not necessary. There is a symbol for nonlinear resistors. And nonlinear inductors. And nonlinear capacitors...

Inspiration for this post, came from here:
https://www.sciencedirect.com/topics/engineering/circuit-theory

Ah, ScienceDirect. There are several articles linked at that page. Which one are you referring to? Could it be this one?
https://www.sciencedirect.com/topics/engineering/nonlinear-resistor

[Circlotron]

There the cats whiskers when compared to many other illuminating devices

I wonder if anyone has succeeded in using a suitably biased LED as an RF detector?

[Kim Christensen]

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?

All we have to do is change the supply voltages.

Or stick an ammeter across each "resistor" in turn. 

[Sredni]

You still don't get the meaning of nonlinear? It means it is NOT linear. The resistance is NOT constant. That is the whole point.
But if you wish I think you could waste some time creating a voltage dependent resistor in LTSpice by copying the V-R characteristic I show above, and then you can change supply voltages all you want.

Nonlinear resistors exist and the term is used in engineering.

Go read the science direct link I posted above.

[Kim Christensen]

I don't need to. I understand the concept 100%. I just don't see the point. 

[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.

[electrodacus]

Ok, this is the VI characteristic of a 1N4148 diode in LTSpice (default temperature) - sorry I went on simulating and picked 1n4148 instead of 1n4007. But it's immaterial.

You can do the same thing for an inductor. Do you consider that all components are just resistors ?
A diode is the equivalent of a one-way valve.
While there is a minimum pressure needed to have the one-way valve open same as a minimum voltage is require for the diode to allow electrons to pass trough.
You will not call a one-way valve a restriction same as you will not call a diode a resistor.
Also one way valve will do what the name implies and allow the fluid to flow only in one direction but same as a diode if the pressure / voltage is high enough it will get damaged and then when they are damaged they are no longer a one-way valve or a diode but your favorite component a resistor.
So I'm OK to call a damaged diode a resistor but a working diode is not a resistor.

A real diode unlike an ideal diode has non ideal characteristics that impact the performance. It has resistance, inductance and capacitance and this non ideal proprieties are refereed to as parasitic elements. This including resistance are not desirable properties.

[Sredni]

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.

[Sredni]

Ok, this is the VI characteristic of a 1N4148 diode in LTSpice (default temperature) - sorry I went on simulating and picked 1n4148 instead of 1n4007. But it's immaterial.

You can do the same thing for an inductor.

No, you can't.
Different state variables.

[BU508A]

A LED is not a resistor.

This is a resistor which can emit light:

[SiliconWizard]

That's, once again, just about modeling. You can model all your heart's content, if you find that fun or see any practical use. Ultimately, it's just MODELS.

You're taking an I-V characteristic, basically, and claim that R = U/I, except that R here is a function of U (or I). Which makes it a dubious use of the "resistor" term, as quite a few have already said.
It doesn't serve much purpose either, other than playing with I-V characteristics, which is something that is pretty basic electronics, and obviously useful in itself.

And yes, inductors and capacitors are a slightly different beast, as they involve derivatives and their model is thus a differential equation. But you can still express them in terms of a relationship between U and I; no pun intended.
If you further twist your definition of a resistor with differential terms, then inductors and capacitors also become "resistors" in your definition.

Obviously that's still playing with models, as real-world parts all have resistive, capactive and inductive components as parasitics, and while useful, even the Shockley approximation is ultimately just for the birds, as someone would say.

[Berni]

Resistor < Linear resistor U Nonlinear resistor
Nonlinear resistor < incandescent lamps U diodes U ...

So, you can still call it a diode, recognize that it is a nonlinear resistor and, as such, that it belongs to the more general set of resistors.

Does this make any sense to you?

It does not make sense.

All resistors exhibit electrical resistance.
All of those semiconductor devices indeed also exhibit electrical resistance.
However not all devices that exhibit electrical resistance are resistors as they are not components purposely designed to implement a well defined resistance.

Does not matter what you understand as "resistor", the vast majority of forum members you are talking to on here understand it as a device specifically designed to implement a well defined amount of resistance. You don't have the authority to redefine established industry words used by others.

What you are trying to say is that a diode exhibits the effect of "electrical resistance" or "resistivity".

This effect is not particularly special and just describes that the device can consume electrical power and turn it into something else,

The point I make is that this is ALL a diode does.
Huge resistance when reverse biased, small resistance when forward biased. This is not a side effect. It is what it does (if we neglect secondary effects due to parasitics in real devices).
It does not store energy in the electric field.
It does not store energy in the magnetic field.
It does not do whatever sorcery a memristor does.
It just oppose a resistance that takes power out of the circuit.

Yes we all agree on here that at some fixed DC operating point a diode acts like resistance.

The point is that a diode is nothing special at doing this. The laws of physics force all power consuming components to look like resistors in steady state DC. This means that at a fixed DC operating point even a memristor is actually just electrical resistance, much like a diode acts as purely electrical resistance at that DC state.

Like what else do you expect an component to do at DC? It can either act as a power source (like a voltage or current source) or it can resist the flow of current hence resistance. There is nothing else for a component to do at DC.

[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.

[Siwastaja]

So,

A resistor is a component, which is purposely made resistor-like.

Most people would agree that to be resistor-like, there are two conditions;

1) Absence (or minimizing) of capacitive and inductive behavior, in other words, lack of time-dependent state (voltage and current are in relationship at any point in time, but not in relationship based on their history)

2) Linearity of the relationship between voltage and current, such that a simple scalar constant defines the relationship.

Sredni accepts (1) but doesn't accept (2).

Second condition is sometimes relaxed - e.g. variable resistors, thermistors, light-dependent resistors - but they are never called just "resistors", but with resistor only as part of the full name.

I don't suggest renaming something which already has another name, though, such as "light-emitting diode", as "non-linear light emitting resistor", even if you technically could. Maybe if it was originally named that way, we would be fine with the name. Then we would likely see Sredni creating a thread about how this non-linear resistor should be actually called a "diode".

[magic]

Resistors are bipolar (non-rectifying), non-light-emitting blue LEDs whose forward voltage just happens to depend on forward current linearly rather than logarithmically.

Prove me wrong

[Gyro]

A LED is not a resistor.

This is a resistor which can emit light:

Its operation has been studied and characterized too (attached, those happy days!).

[m k]

If only tool is a wheatstone bridge...

[Retep]

The poll should have had the option: "No. it is not a resistor, so it has a different name."

[xrunner]

I might start a new thread because this is so interesting -

Do you think a Vise-Grip is a hammer?

After all, I can hammer a nail with a vise-grip. If I give you two pieces of wood with driven nails - can you tell which one had the nails driven with a hammer and which one has nails driven with a vise-grip?

So I want to know if a vise-grip is in fact just another form of a hammer. Prove me wrong.

[PlainName]

Has the poll answers text been changed?

[MK14]

Has the poll answers text been changed?

No, I don't think so.

[armandine2]

I might start a new thread because this is so interesting -

Do you think a Vise-Grip is a hammer?

After all, I can hammer a nail with a vise-grip. If I give you two pieces of wood with driven nails - can you tell which one had the nails driven with a hammer and which one has nails driven with a vise-grip?

So I want to know if a vise-grip is in fact just another form of a hammer. Prove me wrong.

I was also thinking on mechanical lines 

... so if the electrical terms Resistance, Inductance and Capacitance have their mechanical equivalents what is the OPs mechanical device analogous to the LED? 

[Sredni]

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.

[MK14]

I am still NOT convinced.  I don't think an LED and a resistor are the same.

Apart from anything else, an LED is normally used as a light source or indicator.  Functions which a normal, non-overloaded resistor can't do.  At least in the visible spectrum.

[Sredni]

I might start a new thread because this is so interesting -

Do you think a Vise-Grip is a hammer?

After all, I can hammer a nail with a vise-grip. If I give you two pieces of wood with driven nails - can you tell which one had the nails driven with a hammer and which one has nails driven with a vise-grip?

So I want to know if a vise-grip is in fact just another form of a hammer. Prove me wrong.

I was also thinking on mechanical lines 

... so if the electrical terms Resistance, Inductance and Capacitance have their mechanical equivalents what is the OPs mechanical device analogous to the LED? 

Not sure you can find one with the exact same characteristic, it should have to be a dashpot that opposes diminishing resistance with increasing force.
If you consider an ideal diode, well a valve opposes infinite resistance to fluidmotion due to negative flow, and zero resistance to theotion with positive flow.
An electrician's zip tie allows you to slide freely in one direction and blocks the motion in the opposite direction, so it has a friction coefficient that depends on the sign of the force you apply to one end. You can consider it a force dependent friction device.

But maybe there is not an hydraulic or a translational or rotational mechanical analog of an exponential diode.
What is the mechanical analog of a Josephson junction?

[IanB]

what is the OPs mechanical device analogous to the LED?

This is interesting actually. The mechanical equivalent of an electrical diode is a non-return valve in hydraulics. What makes it interesting is that a non-return valve requires fluid flow to operate it (to make it open and close). For example if the valve is open and you want it to close, it requires a small amount of backflow to make it shut off--it is not instantaneous. There is a similar behavior in electrical diodes, where they do not operate until current flows through them. The amount of charge required to switch the state leads to the difference between fast signal diodes and high power diodes that switch more slowly.

[Sredni]

I am still NOT convinced.  I don't think an LED and a resistor are the same.

Apart from anything else, an LED is normally used as a light source or indicator.  Functions which a normal, non-overloaded resistor can't do.  At least in the visible spectrum.

I specified "from the point of view of circuit theory". From the point of view of the circuit it does not matter that the power extracted from the circuit by the diode resistance goes all in heat (IR light), visible light, UV, or chemical energy.

And saying that a LED or a diode is a resistor does not mean they have to be the same thing as another member of the set "resistors". It means that a LED or a diode is one kind of, is a type of, is one member of the wide set resistors.
The set "Resistor" is a set that encompasses linear resistors and nonlinear resistors, and nonlinear resistors include - among others - incandescent lamps, signal diodes, zener diodes, wieners and so on.

"This is Helen, she's a woman"
"Don't be silly! Kate is a woman, and Helen is clearly not Kate! She's not even blonde!!!"
"I assure you, she's a woman, just a different hairtype woman."
"Are you trolling me? The people in Stockholm are laughing at you right now. Look at Inga, that's a woman., and guess what? She's blonde too".



 

[PlainName]

For example if the valve is open and you want it to close, it requires a small amount of backflow to make it shut off

Until springs are invented.

Wouldn't that be a closer analog to a diode? The small amount of pressure required to overcome the spring would be similar to Vf of the diode.

[Sredni]

Resistor < Linear resistor U Nonlinear resistor
Nonlinear resistor < incandescent lamps U diodes U ...

So, you can still call it a diode, recognize that it is a nonlinear resistor and, as such, that it belongs to the more general set of resistors.

Does this make any sense to you?

It does not make sense.

All resistors exhibit electrical resistance.
All of those semiconductor devices indeed also exhibit electrical resistance.
However not all devices that exhibit electrical resistance are resistors as they are not components purposely designed to implement a well defined resistance.

Does not matter what you understand as "resistor", the vast majority of forum members you are talking to on here understand it as a device specifically designed to implement a well defined amount of resistance. You don't have the authority to redefine established industry words used by others.

What you are trying to say is that a diode exhibits the effect of "electrical resistance" or "resistivity".

This effect is not particularly special and just describes that the device can consume electrical power and turn it into something else,

The point I make is that this is ALL a diode does.
Huge resistance when reverse biased, small resistance when forward biased. This is not a side effect. It is what it does (if we neglect secondary effects due to parasitics in real devices).
It does not store energy in the electric field.
It does not store energy in the magnetic field.
It does not do whatever sorcery a memristor does.
It just oppose a resistance that takes power out of the circuit.

Yes we all agree on here that at some fixed DC operating point a diode acts like resistance.

The point is that a diode is nothing special at doing this. The laws of physics force all power consuming components to look like resistors in steady state DC. This means that at a fixed DC operating point even a memristor is actually just electrical resistance, much like a diode acts as purely electrical resistance at that DC state.

Like what else do you expect an component to do at DC? It can either act as a power source (like a voltage or current source) or it can resist the flow of current hence resistance. There is nothing else for a component to do at DC.

There is so much to unpack here but let's consider only the last part.
A capacitor at DC can hold a voltage without passing current; try to do that with a resistor.
An inductor at DC can hold a current without a voltage (if ideal, and a small voltage due to small resistive losses if real). Try to do that with a resistor.
You can use these properties to create memory cells. Try to do that with resistors alone.
I am not well versed in memristors to give an elementary setting that shows their fundamental difference from resistors, but I am pretty confident  you got that part wrong, as well.

Have you looked up the Science Direct link I gave above? I am not redefining industry standard terms: diodes have been considered to be nonlinear resistors for decades. You just wasn't aware of it.

[Sredni]

Second condition is sometimes relaxed - e.g. variable resistors, thermistors, light-dependent resistors - but they are never called just "resistors", but with resistor only as part of the full name.

I don't suggest renaming something which already has another name, though, such as "light-emitting diode", as "non-linear light emitting resistor", even if you technically could. Maybe if it was originally named that way, we would be fine with the name. Then we would likely see Sredni creating a thread about how this non-linear resistor should be actually called a "diode".

This is not about the naming per se, it is about the fundamental nature of a diode from the point of view of the circuit. All it does (neglecting secondary effects) is offering a resistance.

I am not saying that since Helen is a woman, she should be addressed as "woman". You can still call her Helen, but that does not mean she ceases to be a woman. And the fact that Helen and Kate are different individuals does not implies that one of them is not a woman.

Seriously, all this seems to point to a broader problem than I had thought. People here seem to have a problem in understanding set inclusion. Could it be it has been removed from elementary school curricula in the last decades?

[Kim Christensen]

This is not about the naming per se, it is about the fundamental nature of a diode from the point of view of the circuit. All it does (neglecting secondary effects) is offering a resistance.

Now you say it... yet your poll asked this:

Is an LED a resistor?
No. It has a different name, so it is not a resistor
Yes. It is a resistor, just not an ordinary one

You don't seem to realize that no one has an issue with a LED, or any other device, having resistive properties. We have an issue with you calling it a type of resistor.

resistance vs resistor 

[IanB]

You don't seem to realize that no one has an issue with a LED, or any other device, having resistive properties.

Of course Sredni realizes that. But if they acknowledged it, it would not serve the purpose of trolling the forum with a seven page thread.

[bdunham7]

People here seem to have a problem in understanding set inclusion.

The problem isn't most of us not understanding what LEDs are nor how basic set theory works.  The problem seems to be you trying to interweave a poorly constructed semantic argument with a particular type of circuit theory.

I'll leave the circuit theory to others such as switchabl who seems to be more familiar with nonlinear network theory than I am.  If we're going to have a discussion about memristors and the theory that posits them, that should be another thread.  It actually might be an interesting topic, but not an uncontroversial one from what I've read.  If anyone has a copy of or link to Chua's original paper, I'd like to see it as I haven't found it outside of a paywall.

Your semantic argument here seems to be that if you describe something using an adjective and a noun, then what you are describing is automatically a member or subset of the set of things described by the noun alone.  This is quite foolish and not how the English language works.  It is fairly common to describe things using an adjective/noun combination that is inherently oxymoronic.  Non-dairy milk, vegan hamburger, etc.  Whether these specific things are to be included in the larger set depends on the precise nature of what you are describing and the definition of the set, not just word combinations.

If you have a silver Rolex, a gold Rolex and an old Rolex, they are all members of the set Rolex.  However, does that mean that a fake Rolex is a Rolex?

Is a Gunn diode a diode?  Define diode first, then look up what a Gunn diode is and decide. 

The typical, ordinary definition of a resistor is a device that obeys Ohms law, IOW has a nominally linear V/I plot that goes through 0,0.  Thus the term "non-linear resistor" is oxymoronic using this definition and we would not include it in the set.  If you redefine the term 'resistor' to mean something other than what I've stated, then perhaps your definition can include LEDs and so forth.  As many have told you already, most of us would find this inclusion to be unhelpful.  This is not to due to stupidity or some great educational lacuna so please get over yourself and your pseudo-iconoclast act.

[Sredni]

This is not about the naming per se, it is about the fundamental nature of a diode from the point of view of the circuit. All it does (neglecting secondary effects) is offering a resistance.

Now you say it... yet your poll asked this:

Is an LED a resistor?
No. It has a different name, so it is not a resistor
Yes. It is a resistor, just not an ordinary one

You don't seem to realize that no one has an issue with a LED, or any other device, having resistive properties. We have an issue with you calling it a type of resistor.

resistance vs resistor 

Yes, because the mental block a lot of people have in recognizing that a diode (an LED) is a resistor seems rooted in the fact that it has a different name.
As if giving it a specific name could change its fundamental nature.

What a diode does is offering a resistance that changes with voltage or current. You can create a voltage dependent resistor in Spice with the same V-R characteristic of a silicon diode and it will behave the same at every current and voltage.

Have you looked up the Science direct link I gave above? It mentions multiple textbooks using the term nonlinear resistor without even batting an eye, and also acknowledging that a diode is a nonlinear resistor. Do you think they are trolling?

[BU508A]

Do you think they are trolling?

Perhaps not, but I think, you are the troll here. At least in this thread.

[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?

[magic]

Yes, because the mental block a lot of people have in recognizing that a diode (an LED) is a resistor seems rooted in the fact that it has a different name.
As if giving it a specific name could change its fundamental nature.

Have you considered the possibility that the diode was given a different name after some very smart experts realized that it really is a fundamentally different thing than a resistor?
 

[bdunham7]

Go tell Vishay they are using an 'oxymoronic' terminology.
After all what could they know about electronic components?

Calling a term oxymoronic doesn't imply that it is inherently erroneous, merely that there is a tension or conflict between two parts of the term.  I have no problem with the term "nonlinear resistor" and neither does anyone else.  You're tilting at imaginary windmills here.  Oxymoronic terminology is common when seeking to distinguish something from a set while also claiming some similarity, thus my example of non-dairy milk.  I have no issue with the term 'almond milk' as it readily describes the product, but if I ordered a gallon of milk without further specification, I wouldn't be happy if they delivered almond milk. 

Perhaps this brief tutorial will help:

https://www.skillshare.com/en/blog/the-oxymoron-a-terribly-helpful-literary-device/

[Berni]

There is so much to unpack here but let's consider only the last part.
A capacitor at DC can hold a voltage without passing current; try to do that with a resistor.
An inductor at DC can hold a current without a voltage (if ideal, and a small voltage due to small resistive losses if real). Try to do that with a resistor.
You can use these properties to create memory cells. Try to do that with resistors alone.
I am not well versed in memristors to give an elementary setting that shows their fundamental difference from resistors, but I am pretty confident  you got that part wrong, as well.

Have you looked up the Science Direct link I gave above? I am not redefining industry standard terms: diodes have been considered to be nonlinear resistors for decades. You just wasn't aware of it.

Yes and we have names for a resistive device that is designed to be very non linear, the industry standard term for that is a varistor instead of resistor.

If you just generalise all these things are being resistors, then you could also generalize all diodes as diodes (even tho they act very differently), then it falls apart even more as some TVS diodes exhibit a memrisor like behavior (they clamp down and stay clamped until you reduce the current, hence have memory of previous current). But that's besides the point. Diodes exhibiting electrical resistance is nothing special or ground breaking. Everyone in this thread knows about it.

The only problem is that you are throwing around the term resistor and resistance as being the same thing. They are not. The resistor is the industry standard term for a device that is designed to create the effect of resistance in a well defined manner. While electrical resistance is a physics phenomenon where something opposes the flow of current in a electrical circuit.

What is the point you are trying to make with this thread? That a diode has electrical resistance? Or that everything that exhibits electrical resistance should be called a resistor?

[Sredni]

Have you looked up the Science Direct link I gave above? I am not redefining industry standard terms: diodes have been considered to be nonlinear resistors for decades. You just wasn't aware of it.

Yes and we have names for a resistive device that is designed to be very non linear, the industry standard term for that is a varistor instead of resistor.

Ok, let's start from here. In a previous post you wrote

...a resistor where its resistance is strongly affected by the voltage across it is called a varistor or "voltage dependent resistor". So if you are to draw similarities, you can say a diode is a form of asymmetrical varistor.

So, is a varistor a resistor? You wrote right there: "a resistor where [...] is called a varistor or voltage depent resistor. I'd say that you just said a varistor is a special type of resistor.
And since you also write that a diode is a form of asymmetric varistor... What does that make a diode if not a special kind of resistor?

Do you see the cognitive dissonance, now?

The only problem is that you are throwing around the term resistor and resistance as being the same thing.

No. Resistance is the property. Resistor is the component exhibiting the resistive property. If resistance is constant, the resistor is linear; if it is not, it is nonlinear.

They are not. The resistor is the industry standard term for a device that is designed to create the effect of resistance in a well defined manner. While electrical resistance is a physics phenomenon where something opposes the flow of current in a electrical circuit.

What is the point you are trying to make with this thread? That a diode has electrical resistance? Or that everything that exhibits electrical resistance should be called a resistor?

I am trying to uncover the roots of this cognitive dissonance. First you say that varistors are resistors that... And then you say no, they are not resistors, because resistors are only linear.

Go on that Vishay page that shows how to simulate nonlinear resistors (a term that up to a few messages ago you people thought I had invented, LOL) and simulated your resistor with an exponential characteristic. There you have your diode. It is a nonlinear resistor.

[Zero999]

Perhaps a thyristor is another type of resistor, since it has ristor in it?

Nonsense. A resistive load will always result in unity power factor when connected to an AC source. A diode will not give unity power factor, when connected to an AC source, therefore it is not a resistor. End of discussion.

[Kim Christensen]

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. 

[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....

[Sredni]

Ok, it really is basic comprehension of inclusion.
Watch this first
https://youtu.be/5_oCRtEN2pI

Then consider the set of the following elements:

Diodes (has its own name and symbol)
Zener diodes (has its own name and symbol)
Tunnel diodes (has its own name and symbol)
Metal Oxide Varistor (has its own name and symbol)
Neon NE2 lamp (has its own name and symbol)
Incandescent lamp (has its own name and symbol)

This is a set of...
of...



...nonlinear resistors!
Yeahhhhh!

Now take this big huge set of nonlinear resistors, and put it near the set of linear resistors (they also have their own symbol).
What have you got now? What is the set formed by the set of linear and nonlinear resistors?
It's a set of...
...


Resistors!
Yeahhhh!

Since linear resistors are so to speak the default, we give them the short name of resistors (after all they have been introduced with this name in high school). I hope this won't confuse you.
But apparently it does. Big time.

We call ordinary cars just "cars" even if the set of cars includes formula1 race cars. So, in the same vein the set of cars contains the cars you can drive on public road  (which are called just "cars") and the F1 racing cars, which you can't drive on public roads. The F1 cars have their own name, their own circuit, their own regulations but are still part of the greater set "cars", but are disjoint from the set of public road homologated cars (or "cars" in short).

[Kim Christensen]

Ok, it really is basic comprehension of inclusion.

Yea, and you fail it badly! 

And now, I'm going to "unsubscribe" to this thread, and leave you to your "own devices".

[MK14]

This is a set of...
of...



...nonlinear resistors!
Yeahhhhh!

Now take this big huge set of nonlinear resistors, and put it near the set of linear resistors (they also have their own symbol).
What have you got now? What is the set formed by the set of linear and nonlinear resistors?
It's a set of...
...


Resistors!
Yeahhhh!

I hoped (it was somewhat intentional on my part), that my recent post(s) in this thread, would elisit, more information from you (the OP), as to what you thought was going on, and it seems to have worked, as you seemed to have done that.

In summary and as a sort of analogy, this is how I seem to understand, the point(s)/concept(s) you seem to be trying to portray.

(Hypothetically speaking, i.e. I have NOT just done this).
I create an interesting and long new thread on here, describing my new $50,000 electric car, which happens to have (very approximately), a 100 volt battery set up, along with a 100kW motor (engine if you like).  I have then described the technical details, of all its (interesting to some) systems and functionalities.

You have now jumped into my (hypothetical) thread, and said ...
"no no NO NOOOOOOO!!!!, what nonsense MK14 is talking ......"

This is all really a 1 milliohm resistor (non-linear resistor), with a supplied link to a set theory YouTube video, for very young people.

So, although there is a little bit of technical merit (correctness), and the $50,000 new car, is a bit like (sort of, at a stretch of the imagination), a 1 milliohm resistor (non-linear).

The vast bulk of the time, and to almost everyone, it is NOT a useful, interesting or good way of expressing, what it is.

E.g. Which thread title would people be more likely to click on?

"I just bought my great new, $50,000 super fast electric car, technical details of all its electronic systems included, with advanced AI self-driving to level 3"

Or

"Today I bought a 1 milliohm, (non-linear) resistor"?
The start of the thread then says...
100V 100kW (max)


I hope my analogy is accurate?

[TopQuark]

The terms resistor or diode are just words we humans coined to describe certain electrical devices with a specific electrical property, to help us engineers abstractly express how our circuit design works and it's expected behavior.

There's no reason why you couldn't call every 2-leaded device as a resistor:

- A diode is a non-linear resistor that conducts current exponentially with applied voltage, and only in one way
- A capacitor is a giga-ohm resistor with two electrodes that conducts through dielectric materials, it also happen to store charge too. 
- An inductor is a low-value resistor made with coils of copper wire wrapped around something, that also happens to store energy in the magnetic field.

Go ahead, replace all your schematic symbols with resistors.

If a p-n junction can be described as an resistor, they why not draw your pnp junction transistor as a few resistors too?

Go ahead, when your boss or client asks you to design a circuit, send them a page of resistors. Next time you buy a CPU for a PC, ask for a package of 1 billion integrated non-linear resistors too! See what you get.

The fundamental reason a resistor is a resistor, and a diode is not a resistor, is because we engineers decided it is just easier for everyone to agree on using terms to abstractly describe devices with different classes of expected behavior.

It is non productive to call everything "resistor, but non-linear", "resistor, but stores charge", "resistor, but inductive". We decided there's a line in the sand where we split all these "resistors" into different abstract things, giving them different names "diode", "capacitor", "inductor" while reserving "resistor" for the linear device we already understand it to be.

You can invent your own method of describing a circuit. You can invent your own mathematical system. You can invent your new language. We simply agreed on what we commonly use to get everyone on the same page, and not having to explain everything from scratch every single time.

[Berni]

They are not. The resistor is the industry standard term for a device that is designed to create the effect of resistance in a well defined manner. While electrical resistance is a physics phenomenon where something opposes the flow of current in a electrical circuit.

What is the point you are trying to make with this thread? That a diode has electrical resistance? Or that everything that exhibits electrical resistance should be called a resistor?

I am trying to uncover the roots of this cognitive dissonance. First you say that varistors are resistors that... And then you say no, they are not resistors, because resistors are only linear.

Go on that Vishay page that shows how to simulate nonlinear resistors (a term that up to a few messages ago you people thought I had invented, LOL) and simulated your resistor with an exponential characteristic. There you have your diode. It is a nonlinear resistor.

Yes a resistor that is designed to exhibit high nolinearity is called a varistor, this is to not confuse it with a regular resistor that is meant to have just a well defined resistance as the primary characteristic.

So this thread is indeed just about you not agreeing with how things are named.

I don't decide what the industry decides to call things. I just follow the already established naming conventions so that there is no confusion about what we are talking about to the majority of people in the field. The purpose of giving things names is to facilitate communication. Sure not all names for things are the best choice and sometimes they are obsolete historical reasons for the origin of a name, but it is what it is.

The laws of physics don't change if you change the name of a device. This thread shows that the vast majority of forum members agree upon what a resistor is and it also agrees with what Wikipedia defines as a resistor. So i am going to continue using that definition of a resistor as it clearly is the more prevalent industry standard.

Nothing really to gain from arguing about already established naming conventions.
So i am leaving this thread. See ya 

[ebastler]

Sheesh... how long do you guys plan to continue this?

"Resistor", without any qualifier, is used in practice to designate a component which exhibits ohmic resistance. Strictly speaking, one should use the term "ohmic resistor" for that type of component, and reserve the unqualified "resistor" as the generic term for ohmic and non-linear resistors. But in practice, nobody does that.

We also use special terms for non-linear resistors with specific properties -- diode, varistor, NTC, PTC etc. -- and don't refer to them as "resistors". Otherwise, confusion would ensue since "resistor" is so commonly used to refer specifically to ohmic resistors.

So Sredni is right, in a fundamentalist, "how many angels on a pinhead?" kind of way -- which seems to give him great satisfaction. But in practical terms, everybody else is right.

[magic]

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.

Nonsense.

This circuit has almost linear decrease in gain as the input signal increases. Consider for example R1 = 1kΩ:

Vin = 1V, I = 1mA, Vout = -600mV, gain = -0.6
Vin = 2V, I = 2mA, Vout = -618mV, gain = -0.31
Vin = 5V, I = 5mA, Vout = -642mV, gain = -0.13
Vin = 10V, I = 10mA, Vout = -660mV, gain = -0.066

[DenzilPenberthy]

This thread is a truly dumb premise.  So what OP is saying is that literally every single electrical/electronic component that exists is a 'resistor' and that's somehow a useful or interesting observation?

Presumably OP would even pedantically call a superconductor a 'resistor' just 0 Ohms?

This is the same sort of person who spends the whole evening in the pub with friends strenuously arguing that breakfast cereal is a type of soup.

[Sredni]

There's no reason why you couldn't call every 2-leaded device as a resistor:

- A diode is a non-linear resistor that conducts current exponentially with applied voltage, and only in one way
- A capacitor is a giga-ohm resistor with two electrodes that conducts through dielectric materials, it also happen to store charge too. 
- An inductor is a low-value resistor made with coils of copper wire wrapped around something, that also happens to store energy in the magnetic field.

 

No.
Capacitors and inductors are FUNDAMENTALLY different from resistors. How many times do I have to repeat it? There are only four (three in practice) fundamental circuit elements: resistors, capacitors, inductors,(and memristors, but let's forget about them).

I mean, this is the basis of circuit theory.
It's all about what are the state variables that describe their behavior. All you need to describe the state of a circuit at any time are the values of charge q, magnetic flux phi and their derivatives, the current i=dq/dt and the voltage v=dphi/dt.

(Pure) Resistors are components described by a relationship in the V-I plane. If this relationship is a straight line they are linear resistors (but we call them just "resistors" for simplicity). If this relationship is not a straight line they are nonlinear resistors and depending on the particular shape of the characteristic they take many names such as incandescent lamp, varistor, diode, zener diode, tunnel diode, and so on.

(Pure) Capacitors are components described by a relationship in the q-V plane. If this relationship is a straight line they are linear capacitors (we call them "capacitors" for brevity). If the relationship is not a straight line they are nonlinear capacitors. You cannot describe the state of a capacitor by using the values V and I; you need v and the integral of I, that is charge.

(Pure) Inductors are components described by a relationship in the phi-I plane. If this relationship is a straight line they are linear inductors (and in introdoctury courses we call them "inductors" for brevity). If the relationship is not a straight line (because of saturation and hysterisis) they are nonlinear inductors (and we still call them "inductors" because they are very widespread, like the I in SEPIC).
You cannot describe the state of an inductor by just using the values of V and I; you need I and the derivative of V, that is the magnetic flux phi.

And before you say, if I give you the v(t) and I(t) functions I can still find the value of C and L, Think again: you need a function to extract information on the integral or derivative.

What is the value of a (linear) capacitor that has a voltage of 1 volt and a current of 1 mA? You can't find it. But if I tell you that when it has 1 volt across it, it's charge is 1 uC you will immediately tell me it's a 1uF capacitor.

So, no. You CAN'T call a (pure) capacitor a resistor because it is NOT a resistor.
This is the absolute bare minimum of circuit theory.

But you can call a (pure)diode a resistor because it IS a (nonlinear) resistor. Offering a voltage dependent resistance is what it FUNDAMENTALLY does. It's not a matter of naming, it's about it's findamental nature.

You can invent your own method of describing a circuit. You can invent your own mathematical system. You can invent your new language. We simply agreed on what we commonly use to get everyone on the same page, and not having to explain everything from scratch every single time.

You people should start read some books. This is NOT "my" method of describing circuits. This is not "my" language. This is how circuits are described in universities all over the world. It's just that not all textbooks join the dots for you.

[TopQuark]

This is stupid.

https://article.murata.com/en-global/article/insulation-resistance-and-leakage-current-of-capacitor

Capacitors can leak, dielectrics can conduct, it has a I-V curve at DC, so it could be resistive. Your pure, ideal capacitor in your head does not leak, but I look at all the capacitors in my parts storage, and all of them has a leakage current (I) when high enough voltage is applied to it (V). Should I relable it as all resistors?

(Pure) Resistors, (Pure) Capacitors, (Pure) Inductors

Resistance, capacitance, inductance are the words you are looking for. Those are the the theoretical physical properties that are well defined. Resistor, capacitor and inductors are the devices that does mostly what it says in the name, but we all know it isn't perfect. When I put a capacitor symbol in my schematics, I don't mean to spec in two magically floating metal plates separated by a perfect vacuum, I am placing a tube containing a couple strips of foil separated by paper soaked in electrolyte, a.k.a. an electrolytic capacitor on a PCB.

You can say a diode has resistance, which I am sure you can wrangle your math to proudly show it is so, fine, but that does not mean "an LED is a resistor". The ability to use maths and quote books to make pointless arguments proves you have linguistic intelligence, but it does mean not you are an intelligent person.

If you walk up to a straight dude, say he is gay, get punched in the face. You can argue "dude you are dumb, I saw you laughing, and according to the dictionary gay could mean happy, so I was correct. Did you even study English?". Who's the dumb one in this story? 

[Sredni]

I believe this is the sixth time I have to repeat it: in all this discussion I am neglecting parasitic effects. Because I am discussing the FUNDAMENTAL nature of the diode.

A silicon diode described by the exponential Shockley relation, with negligible junction capacitance and negligible inductance of its terminals is FUNDAMENTALLY just a nonlinear resistor, that is: a resistor whose resistance is a function of its voltage.
I also showed the R = R(V) curve in LTSpice.

It does nothing more than that. The nonlinear resistance is its primary and intended function. It is what it makes it a diode.
Unlike the ESR of capacitors and inductors, which is only an undesirable parasitics.

[PlainName]

It is what it makes it a diode

That's what you  keep getting told. A diode has non-linear resistance. A resistor has linear resistance.

[Sredni]

It is what it makes it a diode

That's what you  keep getting told. A diode has non-linear resistance. A resistor has linear resistance.

So you agree that a diode is a nonlinear resistor.

But you don't think that nonlinear resistors are... resistors. Correct?

[Zero999]

Non-linear resistors are not resistors. They are something else: diodes, DIACs, varistors etc. but not resistors. End of discussion.

[tom66]

This whole thread is a meaningless semantic argument, ultimately why does it matter if you want to go against the grain of most engineering and call a diode a resistor with non-linear properties then go ahead... but does it have any use in the real world?  No, it does not.  You can define a diode by a Vf and a few other basic parameters and get a useful result that is close to real world behaviour, but you cannot usefully define a diode by a resistance as the apparent "resistance" varies significantly across the V/I curve.  End of argument.  I really can't believe this has gone on for 9 pages.

[Sredni]

This whole thread is a meaningless semantic argument, ultimately why does it matter if you want to go against the grain of most engineering and call a diode a resistor with non-linear properties then go ahead... but does it have any use in the real world?  No, it does not.  You can define a diode by a Vf and a few other basic parameters and get a useful result that is close to real world behaviour, but you cannot usefully define a diode by a resistance as the apparent "resistance" varies significantly across the V/I curve.  End of argument.  I really can't believe this has gone on for 9 pages.

"Most engineering"? Are you sure that 'most engineering' do not realize the diode is a nonlinear resistor? I mean you can bring a load of vocational school books that do not need to go any further than a superficial hands-on description of the devices, but when it comes to serious engineering books, and even more so circuit theory books, and even more so nonlinear circuits theory books, it is glaring evident that a diode is a nonlinear resistor.

Even mainstream references, like "The Electrical Engineering Handbook" leave no room to ambiguities:

Nonlinear resistors commonly used in electronic circuits are diodes: exponential, zener, and tunnel (Esaki) diodes.

Maybe you can call Elsevier, or Simon Fraser university and tell the author of that chapter that they are going against the grain of 'most engineering'.

It took 9 pages because the objection shifted from "if it's a diode its not a resistor, duh", to "there is no such thing as a nonlinear resistor", to "nonlinear resistors exists but they can only be varistors, lamps, but not diodes", to "diodes are nonlinear resistors but nonlinear resistors are not resistors".

Edit: grammar

[MK14]

Bold and font size change, done by me.

I am curious. How many of you people think an LED is a resistor? I should add: from the point of view of circuit theory, not from that of technology and underlying physics.

(This question originates from a question in another forum, where polls are not possible).

You specifically said "resistor", in the poll.

So you can't start changing the "resistor" to other things, such as "non-linear" resistors, later in the thread.

Because it makes the poll (and possibly the thread), relatively meaningless.

[Sredni]

A nonlinear RESISTOR is a RESISTOR.

nonlinear here is an adjective that specifies a particular property of a subset of the general set of resistors.

A bald man is a man.
A one-legged man is still a man, even if in all medicine books the body of a man is shown with two legs.

A nonlinear inductor is still an inductor.
The inductors used in Single Ended Primary Inductor Converters are usually nonlinear but they are called inductors nonetheless. Have you ever read "the nonlinear coil two-port element's current is..." In the description of a switching circuit? No, everybody says "the inductor's current..."

Sheesh...

[Gyro]

This is getting nobody anywhere...

In the real world, semiconductors, including diodes (of all flavors) have datasheets. These specify the typical and worst case voltage / current characteristics under defined conditions. People find these USEFUL in designing them into circuits and products in the real world. Your dogmatic semantic argument that they are all resistors is NOT USEFUL in the real world. See the distinction?

Your dinner tonight will have electrical resistance, which will be determined by its composition temperature etc. as will the plate it is sitting on, the table they are sitting on, the chair you are sitting on (and the arse you're sitting on it with). Will you sit there making semantic arguments that they should all be defined as resistors until it gets cold (or in your case possibly moldy), or in the real world, will you just eat it?

[MK14]

A nonlinear RESISTOR is a RESISTOR.

nonlinear here is an adjective that specifies a particular property of a subset of the general set of resistors.

If someone in an opening forum post, says "Resistor".  That should mean a component, which obeys (without any trickery or messing around) Ohms Law.  So it can't be a non-linear thing.

If it is (or could be something) which doesn't obey Ohms Law and/or a weird type of resistor.  Then that should be clearly stated in the opening post/poll.

Otherwise, you are moving into the realms of (similar to), trick questions.

When making polls, it is very important that the question(s) and propositions etc.  Are very unambiguous, to a very wide audience.  Otherwise the poll results and possibly the thread, may just descend into massive arguments.

[bdunham7]

A bald man is a man.
A one-legged man is still a man, even if in all medicine books the body of a man is shown with two legs.

How about a fictional man?  Or a robotic man?  An AI man?  A virtual man? 

As I clearly explained earlier--and you appear to have used the concepts I explained and twisted them around to your own ends--something described by an adjective plus a noun does not necessarily belong to the set of things described by the noun alone.  So it all boils down to how you choose to define resistor.  And stop with the bleating that these aren't YOUR definitions but rather those of some famous people we're bound to respect--you don't have to invent the descriptions, they become "yours" if you choose to adopt them.  My definition of convenience is that the term 'resistor' used alone with no prefix means a fixed, nominally linear resistor.  I didn't invent that.

Wikipedia has an interesting statement--"The electrical function of a resistor is specified by its resistance".  I like that.  Is an LED's function specified by a resistance value?  There's an opening for you in that statement, perhaps you'll get another 9 pages out of it.

[PlainName]

It is what it makes it a diode

That's what you  keep getting told. A diode has non-linear resistance. A resistor has linear resistance.

So you agree that a diode is a nonlinear resistor.

But you don't think that nonlinear resistors are... resistors. Correct?

I think you need to take a course in reading comprehension. Ask an optician why you keep seeing 'resistor' where it really says 'resistance'.

[BU508A]

Because I am discussing the FUNDAMENTAL nature of the diode.

This is the fundamental behaviour of a diode. Doesn't really look like a resistor.

[Sredni]

That's a piecewise linear resistor: infinite resistance under threshold voltage, zero resistance above.
Really, this is basic circuit theory.

And no, to answer other objections I use resistor and resistance with care: resistance is the property, resistor is the circuital element.
A linear resistor (generally called "resistor" without adjective) has constant resistance. A nonlinear resistor has voltage or current dependent resistance.

And yes, form the point of view of the circuit all a (linear or nonlinear) resistor does is opposing a resistance and dissipate power. Dissipate means it leaves the circuit. It does not matter in what form: heat, light, chemical energy...
I have simulated LEDs in LTSpice and never saw light coming out of the screen :-)

[AVGresponding]

Every time I glance at this thread, I can feel IQ points evaporating

[bd139]

Is a non-linear resistor, like a thermistor non-linear in at least a small signal model at a set temperature? No it's linear because "R" is constant under those conditions and not dependent on I or V.

The definition of a non-linear resistor is even broken according to the arguments here.

So you can't even reason about the thought framework the question is posed in because it's so poorly defined.

Therefore I posit that it doesn't matter if anyone thinks an LED is a resistor or not, the original poster is a troll trying to be clever, thus is a dickhead and a fuckwit and this thread should be locked.

[edavid]

The original poster is a ... fuckwit and this thread should be locked.

Can we get a button for that?  It's a pain having to type it every time 

[Bud]

Cant believe this garbage thread is still continuing 

[Sredni]

Is a non-linear resistor, like a thermistor non-linear in at least a small signal model at a set temperature? No it's linear because "R" is constant under those conditions and not dependent on I or V.

The definition of a non-linear resistor is even broken according to the arguments here.

You don't understand the difference between small signal and large signal analysis.
You want to lock the thread because of that?
Have you seen the list if references I have given? Are they all troll (and the other names you called me)?

I assure that they, at least, understand what small signal analysis is about.

Again, I do not respond to provocations. If you don't like how Vishay classifies their components, or how experts on circuit theory call the fundamental circuital elements, just don't read this thread.

[fourfathom]

The original poster is a ... fuckwit and this thread should be locked.

Can we get a button for that?  It's a pain having to type it every time 

"JFW" works for me (Just F****** Wow!)

Resistor != Resistance

But it's fun to watch someone being so painfully obtuse.  Also kind of sad.

[bd139]

...or how experts on circuit theory call the fundamental circuital elements, just don't read this thread...

Ok in that case, give me a proof in any suitable domain, other than laplace for obvious reasons but I'm sure you know why that is[1], showing any equivalence between any transfer or large/small signal model of a resistor and an LED where I or V depend on R and not an external factor and vice-versa.

I expect you to explain this mathematically.

[1] feel free to explain for those who don't.

[Sredni]

A bald man is a man.
A one-legged man is still a man, even if in all medicine books the body of a man is shown with two legs.

How about a fictional man?  Or a robotic man?  An AI man?  A virtual man? 

Seriously?
Is a non-car a car?
Is a carrot a car?

We are at this point?
If you had read any of the circuit theory or general engineering books I have given you would know that in order to be part of the set --- let's call "all resistor" the elements need to share a common trait. Like when in that video for kids you have all vegetables in one set and all fruits in another set (and don't bring out the tomato!).

So, what is the common trait shared by the elements of the set "all resistors"? It's that they are fully characterized by a relationship between voltage and current. Only between V and I. Not q and V (those are capacitors) and not phi and I (those are inductors).

So, "all resistors" have a characteristic that is implicitly defined by  f(v, I)=0, that is a curve in the vi plane.

Now, among all these resistors, some have a curve that is a straight line, that is a v + b I = 0, which you can rewrite as v = R I. This is the subset "linear resistors" of the set "all resistors". It is a very important set because it has all the easy to understand properties of linear functions, including superposition. That is why we strive to make our components the more linear possible (yes, the five striped thingies called "resistors" you can buy are actually nonlinear and can only be considered linear within specified limits). Since they are so easy to understand, we teach about them in high school and we simply call them "resistors" not to overload feeble minds with unnecessary complications
 
But the set "(linear) resistors" is not the entire set "all resistors". We are left with all those components that are described by a VI characteristic that is NOT linear, like diodes, scrs, mov, incandescent lamps, neon bulbs... These form the huge subset "nonlinear resistors" of the larger set "all resistors". So, they are resistors with f(v,I) nonlinear.

And no, a carrot is not a car.

[bd139]

You sound like a programmer. Only programmers fuck up taxonomies this badly.

[Simon]

As predicted you started a stupid poll to piss everyone off by changing the question. Why don't you go back to those other forums where got your stupid little smartarse question. Come back when you have grown up!

[EEVblog]

Is this one of those trick questions where you pull a small-signal model out of your hat when everyone's distracted or explain later that when you said "resistor" you didn't actually mean resistor?

No, no trick question at all.
I can even show my hand: it is a resistor, a nonlinear resistor to be precise. Why? because its state is determined by the present values of voltage and current (and not their derivatives and integrals like capacitors, inductors, and memristors).

But a lot of people have trouble in recognizing that.

A diode is a resistor in the same way an incandescent lamp is a resistor. Both are nonlinear and both have exponential V-I characteristics. And yet everyone has no problem in computing power dissipated in circuits with incandescent lamp treating them as resistors, while when it comes to diodes the 'hard' exponential seems to create a mental block.

I just wanted to see how widespread this misconception is.

I've seen it taught that as a non-linear resistor for the purposes of calcuation, but it's not a resistor, it's a diode. Try changing the polarity and see what happens.
By your standard diodes are also resistors, or the B-E junction of a transistor is also a resistor, which is silly.

[Simon]

Dave, I locked the thread and this guy is taking the piss. PM from him:

Hi, have you had a breach in the system?
In the poll "do you think an LED is a resistor?" You wrote that the question was changed.

I just checked and the question is as I first formulated it. Has it been changed by someone else and then reverted back to its original form?