General > General Technical Chat
Do you think an LED is a resistor?
Kim Christensen:
--- Quote from: Sredni on April 23, 2024, 11:31:38 pm ---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.
--- End quote ---
Notice that they didn't write this:
--- Quote ---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.
--- End quote ---
:-DD
Someone:
--- Quote from: Sredni on April 23, 2024, 11:38:36 pm ---
--- Quote from: Someone on April 23, 2024, 11:16:56 pm ---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.
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Yes, this is the only one I have used. Did you not realize it?
--- Quote ---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.
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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.
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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:
--- Quote from: Kim Christensen on April 23, 2024, 11:46:44 pm ---Notice that they didn't write this:
--- Quote ---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.
--- End quote ---
:-DD
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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:
--- Quote ---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[...]
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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:
--- Quote ---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[...]
--- End quote ---
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).
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