Thermal Resistance Calculator

Calculate junction temperature through a chain of thermal resistances from junction to ambient.

W
°C/W
°C/W
°C/W
°C

Junction Temperature

85.0 °C

Total Thermal Resistance12.0 °C/W
Case Temperature70.0 °C

Junction Temperature vs Power Dissipated

Thermal Resistance Chain

Formula

T_junction = T_ambient + P x (θjc + θcs + θsa)

Thermal resistances add in series like electrical resistances. Each interface adds temperature rise per watt of dissipation.

  • θjc: junction to case (from datasheet)
  • θcs: case to heat sink (thermal pad/paste)
  • θsa: heat sink to ambient (heat sink rating)
  • Example Calculation

    5 W dissipation, theta_jc=3, theta_cs=1, theta_sa=8 C/W, 25C ambient.

    1. 01Total theta = 3 + 1 + 8 = 12 C/W
    2. 02T_junction = 25 + 5 x 12 = 85C
    3. 03T_case = 25 + 5 x 9 = 70C

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