Negative Resistance

It sounds like a money-making scam from here.

See these links

http://www.intalek.com/Index/Projects/Research/Negistor.htm

http://www.fact-index.com/n/ne/negative_resistance.html

Negative resistance components and configurations are not ever used to actually save power. You cannot get something for nothing. But tunnel diodes, gyrators and negative impedance converters do have configurations that exhibit a negative resistance slope. These parts though are typically used to generate controllable oscillators or other special case small power analog circuit configurations.

Surprisingly good answers considering the "i am asking for it" OP......i am happy about this.

A tangential thought comes.... Varistors, ubiquitous in electronic circuits...don't they have a "negative resistance slope" .... almost infinity at normal voltage, and practically a short-circuit when the voltage rises. A great device for surge protection.

Actually a varistor is never really a negative resistance where the current decreases immediately as the voltage increases. In a varistor the temperature of the varistor must first change to effectively change the value of the resistance. But in the middle of a discussion on varistors I would not correct anyone about this subtle difference. Unless I was just looking for a fight.

Disclaimers :

1.i am no expert of any kind on Varistors, just curious. i use them though.

2. i am not looking for any fight either, just want to learn more

With that as a given, this paper mentions that varistors react in one nanosecond (hardly enough time for thermal effects perhaps?) and does not mention temperature as a factor for the negative change in the resistance.......

Nice paper, by LittleFuse.

If you look at the initial figure from your paper, the I vs V graph of a Varistor, you will notice that this very non-linear component has either a very high positive slope or a near zero slope. At no time does the slope go negative. (Remember the slope of the I-V curve is the resistance of the component.) So a real negative resistance component will have a I-V slope like this:

The Wikipedia link shows how to make an operational amplifier driven negative resistance input impedance device.

I also have a Mea Culpa to plead. Earlier I confused a thermistor with a varistor. A positive thermal coefficient thermistor will reduce current after a higher voltage self heats the thermistor sufficiently.

Yes, i see that now. Thanks.

There was a great little Polymer-based PTC device called "Prolim" by ABB, which limited all short-circuit currents to 6kA, enabling MCBs to be put on 50kA systems. A flurry of patents came from many companies, Eaton and GE among them. A promising invention, but seems to have withered away...

Here is the ABB patent ... http://www.freepatentsonline.com/5414403.pdf

Apparently you can make a nice one by heating a piece of galvanized steel to a red heat, TAKING CARE NOT TO BREATHE THIS SMOKE, and letting it cool. You'll get small dark spots that have really strange resistance.

Negative resistance I know from loudspeaker design.

It is when the motor coil becomes a generator.

You can not get them ( not even from a catalogue ??!!)

It is just to correct the mathematics you encounter.

I believe some diodes exhibit negative resistance sometimes.

You can not "save power with this effect.