On Saturday, 23 December 2017 11:43:57 UTC, The Natural Philosopher wrote:
On 22/12/17 23:35, tabbypurr wrote:
On Friday, 22 December 2017 17:32:13 UTC, The Natural Philosopher wrote:
On 22/12/17 15:18, tabbypurr wrote:

FWIW silicon devices are often specced to give claimed P_diss at unrealistic case temps, I wouldn't assume any better for other components.

Indeed. But that is not a true usbale 'rating' - that is a measure of
chip to case thermal conductivity.

of course

There is no other way to specify it for a power transistor bolted to a
heat sink of unknowable thermal resistance in an equally unknowable
ambient airflow.

Of course there's another way, give a power figure for realistic conditions. It's marketing innit.


You really have lost te plot you know.

What exactly are 'realistic conditions?
A TO3 bolted to a PCB? To a 3" square finned heatsink? To a massive fan
blown heatsink?

all of those happen, the middle one being the more common.

You are one of those ignorant people who insists on simple answers when
there are none.

er, really? lol

The spec sheet will tell you 5W in free air at 25C and 150W at a CASE
temperature of 25C

As a designer, you then need to look at the thermal resistance of
suitable heat sinks and determine what actual dissipation you can get
away with in a hot steamy discotheque in Botswana....;-)

yeees...
I see you have no valid point with this.


NT