To get 0.9C/W you need an extruded heatsink, very large and heavy. probably about 12" wide, 4" high.I cant find anywhere heat sink for TO220 with the spec:
The total power is ~70W.
So "theta" sink-to-ambient = 0,92°C/W.
It doesn't matter natural or forced cooling.
Thanks in advance.
CORRECT. Thermal resistances add in series. The 4C/W junction-case of the TO-220 is MUCH larger than 0.9C/W. Going to the TO-3 which is <1C/W junction-case saves most of the total thermal resistance.There is also the option of using a different (bigger) package. A TO-3 plus proper heat sink and fan might be smaller than a TO-220 with proper heat sink and fan.
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