Hi All,
I have an existing assembly with two power diodes in series mounted on
an aluminium heat sink, I am increasing the power dissipated on them and
I am trying to do the calculations, to make sure that the diodes will
still be fine using the current setup. 
I started by modelling the assembly:

I will have two branches in parallel of Rjunction-case in series with
Rcase-heatsink and they will be in series with Rheatsink-ambient.

I am just having some difficulty looking at it and need someone to check
if I am thinking correctly. Both diodes will dissipate, in this case,
the same power. The heat will flow from both to the heat sink and then
to ambient. 

Hence if I use the formula
 
                  Tj -(Tcase + Theatsink + Tambient) = Q*(
Rjunction-case + 				Rcase-heatsink +
Rheatsink-ambient)

Where Q is the sum of power dissipated on both diodes


In this case as the diodes are identical is it correct to say that the
Tj you get out of this calculation is the junction temperature for both
the diodes which is also the Tj each of them?

How would you do it for two diodes dissipating different power? It seems
to me that it would not matter, but at the same time I can not be sure,
especially if this power is pulsed instead of continuous.

Any thoughts welcomed.


Best Regards
             Luis

 

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