Heat Sink Thermal Calculator
Junction temp from thermal resistance R_θ
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Heat Sink Thermal Calculator
Junction temperature from power × thermal resistance + ambient. Check T_J vs T_Jmax with safety margin. Required heatsink R_θSA for given specs.
How to use this tool
- 1
Power dissipation
Component power in watts.
- 2
Thermal resistances
Junction-to-case, case-to-sink, sink-to-ambient.
- 3
Junction temperature
Compare to T_jmax.
Frequently Asked Questions
Why R_θJC + R_θCS + R_θSA?
Heat flows in series: junction → case → heatsink → ambient. Each interface has thermal resistance. Total R_θJA = sum. T_J = T_A + (P × R_θJA).
How to choose heatsink R_θSA?
Required R_θSA = (T_Jmax - T_A)/P - R_θJC - R_θCS. Below required = OK. Smaller R_θSA = larger/finned heatsink. Add safety margin (T_Jmax - 25°C).
Thermal interface material?
Thermal grease ~0.5°C/W contribution. Thermal pad ~1-2°C/W. No interface = 5-10°C/W (terrible). For high-power: phase-change pad or grease + good clamping.
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