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Old 13th September 2007, 10:23 AM   #1
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Default NPN negative collector resistance??

at 0.2mA Ib
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Old 13th September 2007, 10:51 AM   #2
OzMikeH is offline OzMikeH  Australia
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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)
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Old 13th September 2007, 11:01 AM   #3
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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).

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Charles
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Old 13th September 2007, 02:23 PM   #4
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Any semiconductor phenomena to judge if this is possible or not?
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Old 13th September 2007, 03:01 PM   #5
Elvee is online now Elvee  Belgium
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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
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Old 13th September 2007, 03:40 PM   #6
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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.
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Old 13th September 2007, 08:11 PM   #7
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Thank you guys, I thought I had lost my head....
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Old 16th September 2007, 06:45 PM   #8
radtech is offline radtech  United States
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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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