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Heatsink Selection Calculator

Calculate the required heatsink thermal resistance (θSA) to keep a device junction below its maximum temperature. Use this to select an appropriate heatsink.

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Formula

θSA=TJ(max)−TAPD−θJC−θCS\theta_{SA} = \frac{T_{J(max)} - T_A}{P_D} - \theta_{JC} - \theta_{CS}
θ_SA — Required heatsink thermal resistance (°C/W)
T_J(max) — Maximum junction temperature (°C)
T_A — Ambient temperature (°C)
P_D — Power dissipation (W)
θ_JC — Junction-to-case thermal resistance (°C/W)
θ_CS — Case-to-heatsink thermal resistance (°C/W)

How It Works

Heatsink selection is a critical thermal management process for electronic components, focusing on preventing thermal failure by managing heat dissipation effectively. The thermal resistance calculation determines the maximum allowable thermal resistance between the semiconductor junction and ambient environment, considering key parameters like maximum junction temperature, ambient temperature, and power dissipation.

Worked Example

Problem: Select a heatsink for a transistor with Tj_max of 150°C, Ta of 25°C, Pd of 10W, θJC of 2°C/W, and θCS of 1°C/W Solution: 1. Calculate θJA_required: (150°C - 25°C) / 10W - 2°C/W - 1°C/W = 12.2°C/W 2. Apply 10% derating: 12.2°C/W * 1.1 = 13.42°C/W 3. Select a heatsink with thermal resistance ≤ 13.42°C/W

Practical Tips

  • ✓Always verify component datasheet for specific thermal specifications
  • ✓Consider airflow and mounting orientation
  • ✓Use thermal interface materials to improve heat transfer

Common Mistakes

  • ✗Ignoring ambient temperature variation
  • ✗Neglecting component-specific thermal resistance
  • ✗Failing to apply manufacturing derating factor

Frequently Asked Questions

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