Thermal Formulas
Thermal formulas relate power dissipation, thermal resistance, and temperature rise across semiconductors and heatsinks. These calculators predict junction temperature and help you choose adequate cooling before a part overheats. They are critical for reliable power and high-density designs.
Thermal Formula Calculators
- Junction Temperature Tj = Ta + P × Rθja
- Full Thermal Chain Tj = Ta + P × (Rθjc + Rθcs + Rθsa)
- Required Heatsink Rθsa = (Tj,max − Ta) / P − Rθjc − Rθcs
- Maximum Power (Junction to Case) Pmax = (Tj − Tc) / θjc
- Thermal Time Constant τ = Cth × Rth
- Forced Convection Heat Transfer Q = h × A × ΔT
- Power Derating (Temperature) Pmax = Prated × (Tmax−T) / (Tmax−Tknee)
- Natural Convection Thermal Resistance Rsa = 1 / (h × A)
- Thermal Runaway Stability Check Stable if dP/dT < 1/Rth_ja
- PCB Copper Thermal Resistance Rth = d / (k × A)
- Cooling Fan Airflow Requirement CFM = P / (1.08 × ΔT)
Related Formula Categories
Browse the full formulas index for all 32 categories.