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Resistance is the slope of current with respect to voltage. If the current decreases as the voltage increases (or vice-versa), the slope is negative, and the device is said to have negative resistance. Examples of such devices are:
. Tunnel Diode
. Transistor in the collector-emitter breakdown region
Regards,
Jon
A negative resistance is often used to create an oscillator:
Each oscillation network (e.g. LC) has losses. These are given from unwanted effects inside the components (resistance of inductor, loss in capacitor) or by radiation in higher frequency ranges. To get your oscillator to work, you have to compensate these losses (which can be described as a real resistor).
Easy said: +R (losses) + -R (device with negative resistance) = 0
I was under the impression that there is no such thing as a 'negative resistance' just like there is no such thing as a negative area! So in the case of resistors, can you say that there is a -10kohm resistor?
There is no such thing as ' -1$ coin ' ,
but sometimes (in real live) you can have -1$ balance on your account
(at first I used the Polish expresion "saldo", my mistake, sorry)
The "negative money" exist in form of written obligation, that you will pay back the money in the future.
It is also possible to built a negative resistance element using for example operational amplifiers and get two terminal element with a characteristic that.
δu /δi < 0 [ohm]
The characteristic It is static (valid also for DC components) and linear with wide range of voltages and currents. It must be supplied from the power supply (but this is not the merit of the negative resistance definition).
During circuit calculation you can simply ignore the complicated structure of the device and replace it by the eqiuivalent resistor of negative kohm value.
negative resistance is nothing but decrease in current ,in increasing voltage.this type of property is found in semicinductor.thermister has also posseses this property.tunnel diode has one region in which it has negative resistance
First you have to know the pos. resistance. By definition R=V/I where current flow throw (into) the resistor. From this we can also define that resistor absorb the power by generating heat. That is positive resistance.
For negative resistance the direction of current is come out of resistor, it generate the power instead of absorbing power. That you can see in oscillator.
From this we can conclude that if you want your design stable (not oscillating) you have to avoid getting neg. resistance in your design. For oscillator you have to design to get neg. resistance.
I hope that will help you to get some ideas about resistance.
Resistance is the slope of current with respect to voltage. If the current decreases as the voltage increases (or vice-versa), the slope is negative, and the device is said to have negative resistance. Examples of such devices are:
. Tunnel Diode
an exact definition wud be from "the illustrated dictionary of electronics" McGrawhill...
"negative resistance 1. A decrease in voltage across a device as the current through it increases, and an increase in voltage as the current decreases. 2. A decrease in current through a device as the voltage across it increases, and an increase in
current as the voltage decreases. This is opposite to the behavior of an ohmic (positive) resistance.
Most replies about negative resistance call out a dynamic resistance .
It is correct , because -R in this form exist in majority of applications (to name generators as an example).
I personally like negative resistance in "pure form" that can be realised as two terminal device as presented in enclosed diagram .
(from : http://ryszardrybka.webpark.pl/wzo.doc )
The "Z" impedance connected to terminals 2 is seen as -Z impedance at terminals 1.
C is seen as L,
R is seen as -R
More about such solutions one can find by searching for the key word "gyrator" .
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