Heat Sink Sizing Calculator
Calculate the maximum allowed heat sink thermal resistance to keep a component within temperature limits.
W
°C
°C/W
°C/W
°C
Max Heat Sink θsa
6.00 °C/W
Total Thermal Budget8.50 °C/W
Used by JC + CS2.50 °C/W
Max Heat Sink θsa vs Power Dissipated
Heat Sink Sizing
Formula
θsa_max = (Tj_max - T_ambient) / P - θjc - θcs
This gives the maximum thermal resistance the heat sink can have. Select a heat sink rated at or below this value. Forced air cooling reduces effective θsa.
Example Calculation
10 W device, Tj_max = 125C, theta_jc = 2, theta_cs = 0.5, ambient = 40C.
- 01Thermal budget = (125 - 40) / 10 = 8.5 C/W
- 02Used = 2 + 0.5 = 2.5 C/W
- 03Max theta_sa = 8.5 - 2.5 = 6.0 C/W
Frequently Asked Questions
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