MOSFET Thermal Design Basics – Heatsink Tips
🔥 The Problem: Why MOSFETs Overheat
When a MOSFET switches high current, it generates heat due to conduction and switching losses. Without proper thermal design, this heat can damage components or reduce efficiency. Many hobbyists overlook heat management, leading to burnt MOSFETs in DIY power supplies, motor drivers, and SMPS circuits.
🛠️ The Solution: Thermal Management Essentials
To keep your MOSFETs cool and safe, use heatsinks, thermal pads, and ensure good PCB layout. Select MOSFETs with low R<sub>DS(on)</sub> and calculate thermal resistance to determine if a heatsink is needed. Always check the datasheet’s max junction temperature (usually 150°C).
🔍 Practical Example :
Let’s say you’re using an IRFZ44N MOSFET switching 10A at 12V.
If its R<sub>DS(on)</sub> = 0.022Ω, power loss =
P = I² × R = 10² × 0.022 = 2.2W.
Without cooling, this 2.2W can push the junction temp beyond safe limits.
📐 Sample Calculation :
Assume thermal resistance from junction to ambient (no heatsink) = 62°C/W:
ΔT = 2.2W × 62°C/W = 136.4°C
If ambient is 30°C, junction reaches ≈166°C — too hot!
Add a heatsink with R<sub>th</sub> = 10°C/W, new ΔT = 2.2 × 10 = 22°C, making it safe.
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