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Topic: Temperature vs Watts (Read 4 times) previous topic - next topic

jluciani

To determine the temperature rise you need to calculate the junction
to ambient thermal resistance (Tja) ---

Tja = Tjc + Tcs + Tsa   all the dimensions are DegC/W

Tjc thermal resistance between the IC junction and IC case.  This is
   from the IC datasheet.

Tcs thermal resistance between the IC case and your heatsink. This
   should also be in the IC datasheet. Usually you place a thermal
   compound between the IC case and the heat sink to decrease the
   thermal resistance.  The decrease occurs because the thermal
   compound fills the air gaps between the two surfaces and conducts
   heat better than the air.

Tsa thermal resistance between the heatsink and ambient air. This is
   in the heatsink datasheet. Most heatsink datasheets specify Tsa
   with and without airflow. You can determine if you need a fan by
   reviewing this number.

For a single heatsource the junction temperature would be

Tj = Tja * P + Tamb  (DegC)

where P is the power dissipated in the IC and Ta is the ambient
temperature.

(* jcl *)

Jassper

jluciani
Thanks for that info, I searched for hours last night on the web and never came across anything that put it into simply terms like you did. Thanks

jluciani

You're welcome.

Since I've answered this question a few times on different lists I decided to
save the answer and re-post as needed  ;)

(* jcl *)

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