Power Management
A 50 W CPU is fitted with a cooler of thermal resistance 0.5 K/W. Roughly how many degrees above ambient does the chip run (ignoring other heat paths)?
- AAbout 100°C
- BAbout 25°C
- CAbout 0.01°C
Show answer and explanation
Answer: B. About 25°C
Thermal resistance is the temperature rise per watt of heat flow, so temperature rise = power × thermal resistance. 50 W × 0.5 K/W = 25 K, so with 25°C ambient the chip sits around 50°C. Doubling power doubles the rise, so working backward from the allowed temperature determines the usable power limit or the cooler performance required.
- A. Multiply by the thermal resistance; do not divide.
- B. Correct. 50 × 0.5 = 25.
- C. That divides by the thermal resistance.