Step-by-step method
- Always check units, prefixes and order of magnitude.
- Estimate semiconductor junction temperature, total thermal resistance and maximum power.
- Compare the result with temperature, tolerances and real conditions.
Semiconductor thermal dissipation
Estimate semiconductor junction temperature, total thermal resistance and maximum power.
Calculate
Junction temperature
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Total thermal resistance
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Theoretical maximum power
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Thermal margin
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Mistakes to avoid
- Always check units, prefixes and order of magnitude.
- Do not use an ideal result without margin or a datasheet check.
- Compare the result with temperature, tolerances and real conditions.
Component selection
Select heatsink and interface with margin; check transient thermal impedance for pulses and varying cycles.
Worked example
At 5 W, 25 °C ambient and 12 °C/W total, the junction reaches about 85 °C.
Limits and safety
Datasheet thermal resistance depends on package, PCB, mounting, airflow and measurement conditions.
Technical sources
Do not use an ideal result without margin or a datasheet check.