> I can then say that if one of the diodes is > on the heatsink but is not dissipating any power, > its Tj will be the same as the calculated heatsink, > which will be due to the power dissipated by the other diode? Of course, except for the probably a small effect of the cooling via the Rth body-ambient of the inactive diode. > So now I am thinking, what happens if you have this heatsink inside a > box? You will heat the air and hence your Tj will start to increase, > hence I need cooling, to reduce ambient temperature in the box. > How do I calculate this? I dunno. Safest thing to do is to provide enough air flow, forced (ventilator) or natural. > Also what about water cooling, what is the process to calculate > requirements? In most cases the water part will be a low Rth, it simply dislocates the Rth X-to-air. -- Wouter van Ooijen -- ------------------------------------------- Van Ooijen Technische Informatica: www.voti.nl consultancy, development, PICmicro products docent Hogeschool van Utrecht: www.voti.nl/hvu -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist