I just mentioned metal core pcbs because I make my own..
I was just trying to find another excuse to use it..
So... it's not very effective to heat sink (by Cu trace or mcpcb) a
2512,2010 or 1206 chip resistor in this case to handle a 26mJ energy
burst..
I'll go for that.
Thanks..
I guess my weak spot in heat dynamics is showing
Join the club. Even if you know the theory, the practical issues -
finding reliable data, modeling 3D distributed diffusive systems,
estimating reliability vs temp - are still fuzzy. [envision global
warming rant here]. At least most thermal conduction systems are
linear, sort of.
All I know is this:
Heat has a propagation time.
Materials have thermal resistance.
Most materials increase in resistance with heat.
Materials decompose if spot is hot enough.
Heating an object is like charging a capacitor???
Yes. There's a direct similarity between thermal and electrical
circuits. You can model thermal things with Spice, making the simple
equivalences
1 volt == 1 degree C
1 amp electrical == 1 watt thermal
1 farad == 1 gram aluminum
1 ohm == 1 degc/watt
1 second == 1 second
which is good to about 5%. There's no thermal equivalent of an
inductor. The bitch is that, while circuits are usually lumped,
thermal systems are often distributed, so diffusion equations apply.
Yuk.
At first I didn't quite understand what was meant by tau...It clicked
in about 1 hour later...
Thermal time constant, how fast a thing transitions to its
steady-state temperature. Can range from nanoseconds to kiloyears.
They estimate time of death by how much a body has cooled down.
If a device has a thermal tau of, say 1 second, it will jump about
1/10th of the way to its steady-state temp if you pulse it for 0.1
second.
This is excellent, and free:
http://web.mit.edu/lienhard/www/downloadform1.html
John