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Home > Archive > Electrical Engineering > March 2007 > MOSFET I vs. T curve
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| Author |
MOSFET I vs. T curve
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| John E. 2007-03-13, 5:25 pm |
| As junction temp increases, r goes up and I goes down, right?
This must be a misprint:
<www.cgi/http://www.allcomponents.ru...antx2n7224.gif?>
(This is IRFM150/2N7224)
(see fig. 1 & 2 on p. 4). I think these 2 graphs are transposed. The higher
condition should result in less current, yes?
Just testing my grasp of the knowledge...
Thanks,
--
John English
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| Robert Baer 2007-03-13, 5:25 pm |
| John E. wrote:
> As junction temp increases, r goes up and I goes down, right?
>
> This must be a misprint:
> <www.cgi/http://www.allcomponents.ru...antx2n7224.gif?>
>
> (This is IRFM150/2N7224)
>
> (see fig. 1 & 2 on p. 4). I think these 2 graphs are transposed. The higher
> condition should result in less current, yes?
>
> Just testing my grasp of the knowledge...
>
> Thanks,
Page 4 of a GIF??????
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| Robert Baer 2007-03-13, 5:25 pm |
| John E. wrote:
> As junction temp increases, r goes up and I goes down, right?
>
> This must be a misprint:
> <www.cgi/http://www.allcomponents.ru...antx2n7224.gif?>
>
> (This is IRFM150/2N7224)
>
> (see fig. 1 & 2 on p. 4). I think these 2 graphs are transposed. The higher
> condition should result in less current, yes?
>
> Just testing my grasp of the knowledge...
>
> Thanks,
NOT FOUND in DigiKey; either 2N7224 or IRFM150.
Fantasy?
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| cr500r 2007-03-13, 8:25 pm |
| "John E." <incognito@yahoo.com> wrote in message
news:0001HW.C21C739301833A49F01826C8@news.sf.sbcglobal.net...
> Sorry:
>
> <http://www.allcomponents.ru/irf/jantx2n7224.htm>
>
> Click on the data sheet image.
>
> Thanks,
> --
> John English
>
The graphs look correct to me.
BTW there is no I vs. T curve, it's R vs. T on fig 4, page 4, and none of
the other graphs are even close to I vs. T.
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| John E. wrote:
> As junction temp increases, r goes up and I goes down, right?
>
> This must be a misprint:
> <www.cgi/http://www.allcomponents.ru...antx2n7224.gif?>
>
> (This is IRFM150/2N7224)
>
> (see fig. 1 & 2 on p. 4). I think these 2 graphs are transposed. The higher
> condition should result in less current, yes?
>
> Just testing my grasp of the knowledge...
>
> Thanks,
In the graphs you're looking at, you can hold Vds constant (say one
volt) and compare Id at the two temperatures. It is clear that r
decreases with increases in temperature. More carriers or something.
Isn't that a characteristic of all junctions?
You will find a similar result for the IRF510, for example.
Chuck
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http://www.droptable.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
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| Robert Baer 2007-03-14, 3:25 am |
| John E. wrote:
> Sorry:
>
> <http://www.allcomponents.ru/irf/jantx2n7224.htm>
>
> Click on the data sheet image.
>
> Thanks,
Look carefully; the figures are correct; it takes a lower Vgs for a
given Id at 500V (linear current sink region) and one gets a lower
Rds(on) at a given gate drive (look at Vds=1V, Vgs=7.0V).
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| Tim Williams 2007-03-14, 9:25 am |
| Gate threshold voltage has a negative coefficient, so falls with temperature
(causing the Vgs = 4.5V curve to move up from about 1.1 to 4.5A). This can
cause runaway conditions in paralleled linear circutis.
Rds(on) rises, as can be seen by looking at the saturated region of the,
say, Vg = 15V curve: at 1V, Ids falls from about 30 to 17A. This causes
stability in paralleled switching circuits (unlike bare silicon junctions in
diodes and BJTs, and to a lesser extent, IGBTs).
It can be seen in Fig.4 that Rds rises about by a factor of 2 from 25 to
150°C, so my rough reading of the log plot is within reason.
Tim
--
Deep Fryer: A very philosophical monk.
Website @ http://webpages.charter.net/dawill/tmoranwms
"John E." <incognito@yahoo.com> wrote in message
news:0001HW.C21C5846017CD46DF01826C8@news.sf.sbcglobal.net...
> As junction temp increases, r goes up and I goes down, right?
>
> This must be a misprint:
> <www.cgi/http://www.allcomponents.ru...antx2n7224.gif?>
>
> (This is IRFM150/2N7224)
>
> (see fig. 1 & 2 on p. 4). I think these 2 graphs are transposed. The
higher
> condition should result in less current, yes?
>
> Just testing my grasp of the knowledge...
>
> Thanks,
> --
> John English
>
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