What Is the Heat Sink Thermal Resistance Calculator?
The Heat Sink Thermal Resistance Calculator sizes heat sinks for power transistors, CPUs, and LED modules to prevent semiconductor burnout.
How Does the Heat Sink Thermal Resistance Calculator Work?
Applies thermal Ohm’s Law across the three-stage conduction network (Junction → Case → Sink → Ambient).
Heat Sink Thermal Resistance Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
R_{sa} \le \frac{T_{j,max} - T_{margin} - T_{amb}}{P_{diss}} - R_{jc} - R_{cs}
Thermal circuit resistance chain equating temperature rise to power dissipation.
How to Use the Heat Sink Thermal Resistance Calculator
- Enter dissipated electrical wattage.
- Input maximum silicon temperature and worst-case ambient temperature.
- Specify internal package resistance R_jc and thermal grease resistance R_cs.
- Select a commercially available heat sink rated at or below the calculated R_sa.
Step-by-Step Example Calculation
Power MOSFET Sizing in Enclosed Chassis
Input Values:
powerDissipation:25
maxJunctionTemp:125
ambientTemp:40
thermalResistanceJc:1.2
thermalResistanceCs:0.5
safetyMarginTemp:15
Worked Steps: Requires heat sink with thermal resistance R_sa ≤ 1.10 °C/W.
Understanding Your Result
Required R_sa: Maximum thermal resistance allowable for the heatsink.
Total R_ja: System-wide thermal impedance.
Case & Sink Temperatures: Expected operating steady-state temperatures.
Factors That Affect the Result
- Adding forced fan airflow dramatically reduces heat sink R_sa compared to natural convection.
When Should You Use This Calculator?
- Power supply design, audio amplifiers, motor drives, and computer CPU cooler sizing.
Assumptions & Limitations
- Assumes steady-state thermal equilibrium without accounting for transient heat capacity.
Frequently Asked Questions
Calculation Accuracy & Reference Note
Standard IEEE/JEDEC thermal resistance modeling.