Active devices can also exhibit a negative resitance, but again, there
has to be some source of power, since a negative resistance sources
power to whatever is connected to it.



I was thinking the neon lamp could display negative resistance at certain
voltage/current ranges. The tunnel diode can also.
Not sure right off it they are active devices or not without looking at some
old information I have.

"Ralph Mowery" wrote in message
ink.net...
Active devices can also exhibit a negative resitance, but again, there
has to be some source of power, since a negative resistance sources
power to whatever is connected to it.



I was thinking the neon lamp could display negative resistance at certain
voltage/current ranges. The tunnel diode can also.
Not sure right off it they are active devices or not without looking at
some
old information I have.


Hi, Ralph -

Yes, I am familiar with tunnel diodes from way back in the 60's. They were
GE devices as I recall. In fact, until about 10 years ago, I had an even
older schematic from an EDN magazine article that showed how to connect two
NPN transistors together to emulate a tunnel diode. Looked sort of like a
bistable connection, as I recall.

Anyway, that's why I limited my statements to passive devices although, as
Roy pointed out, I did not state that I had only one source.

Thanks.

John

To test a device, connect a resistor to its terminals. If the resistor
gets warm, you have a negative resistance.

The neon lamp and tunnel diode exhibit a negative *dynamic* resistance.
That it, the *slope* of the V/I curve is negative at some parts of the
range. They don't exhibit a true negative resistance -- that is, under
no conditions will you find the value of V/I to be negative.

Roy Lewallen, W7EL

Ralph Mowery wrote:

I was thinking the neon lamp could display negative resistance at certain
voltage/current ranges. The tunnel diode can also.
Not sure right off it they are active devices or not without looking at some
old information I have.