On Sep 22, 2006, at 11:57 AM, Forrest W. Christian wrote:

>
>> I already have that. Still does not give me the depth
>> I want on semiconductor theory:( Theory of the
>> behavior of the silicon for a given environment or
>> operation.
>>
> I'm not aware of any book which specifically deals with that

Yeah, semiconductor theory tends to start deep in theory and doens't
quite get up to the "practical" level of things like power dissipation.
Manufacturer literature starts way up with the practical limits and
never gets down to their theoretical causes.

IIRC, at least some of the current limits are related to things
like the carrier density, ohmic resistance of contacts, junctions,
and channels, and so on.  Some of that will be covered in solid
state physics texts; I see a bunch of stuff that I don't understand
any more in my college copy of "Solid State Electronic Devices" by
Streetman (c  1972, so...)  The practical aspects may be deep company
I.P., some secret, some patented.  High power mosfets seem to commonly
be a bunch of parallel devices in a single package, for instance.

If you think of the maximum current as being imposed by the
solid state physics of the internal device, while the power
rating is determined by needing to maintain a temperature where
the solid state physics still applies (even before wires melt,
I seem to recall that temperature has assorted effects on carrier
mobility and such), you won't be TOO far wrong.  It's also possible
that a device was fabricated and then measured, and what you see
in the spec sheet is the max current where the device behaved in
a way that the company wanted to take credit for (ie it is at least
partially derived experimentally.)

BillW
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