What Are Thermal Resistance and Heat Management?
Thermal resistance is the value that shows how hard it is for heat to flow from a component to its surroundings; its unit is °C/W. It's similar to electrical resistance: high thermal resistance means heat is dumped poorly (the component runs very hot).
What Is Thermal Resistance?
°C/W tells you "how many degrees the component heats up per 1 watt of power." For example, 2 W over a 5 °C/W path produces a temperature rise of 2 × 5 = 10 °C.
Junction Temperature
The hottest point inside a chip is the junction temperature, and it must not exceed the limit stated in the datasheet (e.g. 150 °C). The power dissipated and the thermal resistance set this temperature.
The Heat Path and the Heat Sink
Heat flows from the chip to its body, then to the heat sink and into the air. Each stage has a thermal resistance; the lower the total, the cooler the component stays.
| Measure | Function |
|---|---|
| Heat sink | Enlarges the surface, dumps heat into the air |
| Thermal paste | Improves component-to-sink contact |
| Fan | Boosts cooling with airflow |
Common Mistakes
- Skipping thermal paste: an air gap seriously worsens heat transfer.
- Undersized heat sink: the sink must match the power component's wattage; a small one isn't enough.
- Exceeding the junction limit: if the datasheet's maximum temperature is exceeded, the chip fails.
Frequently Asked Questions
What does °C/W mean?+
Does every power component need a heat sink?+
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