a question about resistors in an arc experiment

What's it take, maybe a minute?

As for importing netlists, I'm sure LTspice can do it. You sure can do it in PSpice... actually it's "Run" circuitname.cir

...Jim Thompson

I enjoy the Folsom Street S/M Fair. And lesbian weddings. Skiing out of control. Brainstorming wild ideas in front of customers. Reading outrageous stuff, like history. Eating strange food. I live in one of the wildest and most diverse cities on the planet, by choice. I must not understand your definition of "prissy."

Don't be silly. Pop psychology isn't in your skill set. Circuit design seems to be enough of a challenge.

Personally, I've adapted my personality to do good engineering. It's working.

I seek no followers, or anyone to follow. I can, and do, turn off the TV set and don't subscribe to People Magazine. The trash that modern culture has become saddens me, but doesn't affect me much.

He managed to kill himself, too, depriving us of his brilliance.

As someone in the entertainment biz said, killing yourself can be a good career move.

John

Hey, prongie, post some circuits. Maybe even ones that work.

John

Maybe because he is coarse, rude, has a scat fetish, and he's Always Wrong. But there's no accounting for taste.

John

I've met a couple of COBOL programmers - the one seemed quite level-headed, and after all, how hard is it to write COBOL? The other one asked me to tutor her, but that was just a ruse to get into my knickers. >:->

Cheers! Rich

OK, I can nitpick too - we're not even talking about a "negative resistor"

- obviously, such a thing can't exist. What we're talking about is "negative resistANCE", which is a characteristic of various things, notably, and arc, a UJT, or a tunnel diode.

Hope This Helps! Rich

If it's posted as an attachment (probably have to be in a binaries group) I can just click on it from Agent (I have .asc or whatever it is associated with LTSpice).

But please don't do that. It's great that, partly thanks to LTSPice and AACircuit, we can still easily exchange circuits in these non-binary groups.

Don't you just hate it when that happens?

John

As far as I can tell, the current meter in LTspice tells which way the resistor is oriented. It doesn't say which way the current is flowing. If you flip the resistor 180 degrees, the current meter points the opposite direction, even though nothing else has changed.

I am unable to find a reference in the LTspice documentation that explains how this is supposed to work, but that doesn't mean it is not there.

For netlists, if someone is using XNews and uses the attachment option for the ASC and PLT files, XNews will save them to the directory you specify with the original filenames. You can then run the file normally as you would any other LTspice file.

This has a number of drawbacks. XNews changes the thread title, so your post disappears from the current thread and people are not likely to see it. Also, this behavior may be unique to XNews and the other news clients may behave differently.

For saving netlists, I wrote my own editor and have a function that selects the entire block with one keystroke, then a second keystroke allows me to enter a fileame and save it. But my editor won't run on your system.

Mike

Well, the sex was OK (after all, is there any such thing as _bad_ sex?), but after, she'd leave without even kissing me. I felt like the way a woman must feel when a guy does a slam-bam-thank-you-maam and runs away.

I didn't like that part very much.

Thanks, Rich

Then how does it make your life better to anoint yourself arbiter of it?

Thanks, Rich

I have no power to be an arbiter; what gave you the idea that I do?

But I can certainly have personal preferences and opinions, just as you do. And in an electronics newsgroup, I prefer the electronics to be right.

John

And it would be a good counter, if what you had provided actually looked like a negative resistance in that situation. But it doesn't. Measure the current going in, and you'll find it's positive - that is, that the circuit presents a positive resistance, not a negative one.

Sylvia.

We're not talking about a negative resistance characteristic in this subthread. We're talking about total negative resistance.

Sylvia.

I don't see why a negative resistor would do that. Of course, we have the problem of hypothesising a physcial mechanism for something we're pretty sure can't exist anyway, but to the extent we can think past that obstacle, I can't see why an unattached negative resistor wouldn't just lie there quietly with no voltage and no current.

Sylvia.

In a noiseless world it would. But if somehow its terminal voltage got to be any amount nonzero, no matter how small, it would begin to source current in the direction such as to reinforce that voltage, and awwwwway we go. Any thermal or quantum fluctuation would be enough to set it off.

Spice will allow perfectly noiseless positive-feedback states to persist forever, for want of a direction to go in, the equivalent of a pencil balanced on its point for a zillion years. One sometimes has to poke in a tiny initial condition to shake things up.

Oh, I was wrong about the first circuit not working. It is a different kind of negative resistance, one that accepts a current drive and reacts with a "backwards" voltage response, but goes bonkers if driven by a voltage source. The second circuit is stable if driven by a voltage source, and reacts with a negative current, but explodes if you leave it open. Both dump power *into* the source.

Just tried it in Lt Spice. A -10 ohm resistor in parallel with a 1F capacitor will sit quietly forever. But goose it with a really tiny current pulse, just once, and the voltage takes off exponentially. Cool. LT Spice seems to use the second type negative resistor.

I still can't get my head around the fundamental reason why there's only one kind of positive resistor but two kinds of negative resistor.

John