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AN920

Negative resistance experiment

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Here is a simple experiment to see the effect of negative restance from a reversed biased transistor. It will happen at a certain bias level. If you copy my circuit then the same values should work for you.

We would expect the voltage to decrease when we add resistor R2 as we will be drawing more current through R1. The opposite happens. The voltage increase by 1 volt. Read more on Google about negative resistance to understand this.

This won't work using a circuit simulator.

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Hi AN920

I thank you for your wonderful to deliver some of the concepts that are new, at least for me.
I want to know from a practicle perspective, I want to know the importance of this subject. Where we need to calculate the -ve resistance?
I did some search and get the following:
http://www.st-andrews.ac.uk/~jcgl/Scots_Guide/RadCom/part5/page1.html
I'll discuss with you:
(1)

Considering the amount of attention given to superconducting materials which have an effective electrical resistance of zero it is surprising that the property usually called Negative Resistance is so little known.

From this i understand that Negative Resistance = superconducting.

(2)
fig1.gif
In general, the current tends to rise with increasing voltage, but there is a region between the peak voltage and valley voltage, where the the current falls as the voltage is increased. This is called the Negative Resistance Region because in this voltage range the dynamic resistance, r<0 .

I think that this is the best simplified  definition of the concept of the Negative Resistance. Did agrees with me?

(3)If you read the rest of the page and saw the pictures following, you'll know that there were three cases :
fig2.gif
fig3.gif

a- R be greater than 0 . This is the factual situation that we know.
b- R be equal to 0, a situation virtually impossible.
c- Or to be less than 0, and here I ask how it can be made so?

After receiving reply I'll discuss with u the contents of the next page :
http://en.wikipedia.org/wiki/Negative_resistance

thank u very much

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Rather think of negative resistance as a negative differential resistance that behaves opposite to ohms law in that region. Some high frequency diodes also have this property, with the tunnel diode the most well known. Uni-junction transistors also operate on this principle.

Another configuration you may want to lookup is the "lambda diode" that can be constructed with JFET's or a JFET-bipolar combination.

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Hi Ann
I wish that the dialogue is always reply point by point. I spend a long time in the preparation of the question therefore hope that the reply on the points that I'm asking about them specifically and not a general answer.
The question that I wish to find a definitive answer for is : Why must know -ve resistance, and when necessary to developer in mind?
thanks

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Hello AN920,

You could also review quantum tunneling which has a very similar outline.

Where the wavelength of a particle's wave function is inversely proportional to the momentum of the electron.
The concept behind negative resistance has been discussed a long time ago; noted in klystron/magnetron tube theory.
However, today the theory is actually being applied in a more versatile manner.

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