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-   -   NPN negative collector resistance?? (http://www.diyaudio.com/forums/parts/108442-npn-negative-collector-resistance.html)

darkfenriz 13th September 2007 09:23 AM

NPN negative collector resistance??
 
2 Attachment(s)
at 0.2mA Ib :confused:

OzMikeH 13th September 2007 09:51 AM

Perhaps I am reading the graph wrong but the reistance is still greater than zero, the trend is that the resistance reduces very slightly with increasing voltage.

I think there are cases of negagitive resistance in theoretical applications, the standard unit of negative resistance is the "Mho"
(that may be a joke at my expense when I was an apprentice, I have never encountered it personally)

phase_accurate 13th September 2007 10:01 AM

It does inded show a negative dynamic resistance. But I assume it is an issue of plotting accuracy.
Otherwise it can be used to build oscillators (like tunnel diodes).

Regards

Charles

darkfenriz 13th September 2007 01:23 PM

Any semiconductor phenomena to judge if this is possible or not?

Elvee 13th September 2007 02:01 PM

Hi

A number of phenomena can cause a negative resitance; but generally, it's the other variety, ie an increase in current causing a decrease of the voltage across the device (avalanche+injection, diacs, etc).
This one is rather unusual, and I suppose Charles is right: it has to be an artefact. With an FET in the right conditions, it could be caused by thermal effects, but in a bipolar, it's rather the other way round.
LV

PigletsDad 13th September 2007 02:40 PM

I expect it is just a drafting mistake.

The curves for most bipolars in this region fit pretty well to constant Early voltage.

I would expect the product of output resistance and collector current to be roughly constant - this product is the Early voltage.

darkfenriz 13th September 2007 07:11 PM

Thank you guys, I thought I had lost my head....

radtech 16th September 2007 05:45 PM

Quote:

Originally posted by OzMikeH
the standard unit of negative resistance is the "Mho"
(that may be a joke at my expense when I was an apprentice, I have never encountered it personally)


The term 'mho' was used in the past as the unit of electrical conductance, the reciprocal of resistance (1/R). The term has been replaced by 'siemens'.


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