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Power Dissipation & Thermal Calculator
This calculator estimates power dissipation, temperature rise, junction temperature, and thermal margin for power semiconductors. It is useful for SCRs, TRIACs, MOSFETs, IGBTs, diodes, rectifiers, voltage regulators, and other power devices that require thermal design.
Input Parameters
Results
For SCRs, TRIACs, diodes, and regulators, conduction loss is often the dominant heat source. For MOSFETs and IGBTs, switching loss and switching frequency may also be important.
Equations Used
Conduction Loss:
Pcond = I × Vdrop × Duty Cycle
Total Power Dissipation:
PD = Pcond + Pswitch
Temperature Rise:
ΔT = PD × θJA
Junction Temperature:
TJ = TA + ΔT
Thermal Margin:
Margin = TJ(max) - TJ
Required Thermal Resistance:
θJA(required) = (TJ(max) - TA) / PD
Where:
I = load current
Vdrop = on-state voltage drop or equivalent conduction voltage
PD = total device power dissipation
θJA = junction-to-ambient thermal resistance
TA = ambient temperature
TJ = junction temperature
Frequently Asked Questions (FAQ)
Q1: What does this power dissipation calculator do?
It estimates semiconductor power loss, temperature rise, junction temperature, thermal margin, and required thermal resistance.
Q2: Can this calculator be used for SCRs?
Yes. For SCRs and TRIACs, enter the RMS or average load current according to your design method, the on-state voltage drop, and the conduction duty cycle.
Q3: Can this be used for MOSFETs and IGBTs?
Yes, but use caution. MOSFET conduction loss is often calculated from I² × RDS(on), while this simplified calculator uses an equivalent voltage drop. Add switching loss separately.
Q4: What is θJA?
θJA is junction-to-ambient thermal resistance. It describes how much the junction temperature rises per watt of dissipated power.
Q5: What if the thermal margin is negative?
A negative margin means the estimated junction temperature exceeds the selected maximum limit. The design needs lower loss, better cooling, or a larger package/heatsink.
Q6: Why include switching loss?
In high-frequency converters, MOSFETs and IGBTs can dissipate significant switching energy. This loss should be added to conduction loss for thermal checking.
