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Heat-Sink Thermal Resistance

Heat flows through a series of thermal resistances (°C/W) like current through resistors: Tj = Ta + P·(Rjc + Rcs + Rsa). Solve for the heat-sink resistance (Rsa) you need, or the junction temperature you'll get, or the power you can dissipate.

Power dissipated P (W)

Ambient Ta (°C)

Max junction Tj (°C)

θjc — junction→case

θcs — case→sink (interface)

Required heat-sink θsa

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Max power at this θsa=required

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Steady-state 1-D resistance network. A helper, not a substitute for engineering judgment.