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MOSFET I vs. T curve


Robert Baer

Jan 1, 1970


Jan 1, 1970
John said:
As junction temp increases, r goes up and I goes down, right?

This must be a misprint:

(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...


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.


Tim Williams

Jan 1, 1970
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.