The current rating is not the thermal answer
Linear Regulator Thermal Calculator
Estimate the heat created by a linear regulator, the resulting junction temperature, and whether the input still clears the required dropout at your chosen operating point.
Written and verified by John Merton · verified 2026-07-12
Put your board in the equation
Thermal and dropout estimate
What the calculator does
- Load dissipation
- (VIN − VOUT) × ILOAD
- Ground-current dissipation
- VIN × IGND
- Estimated junction
- ambient + total dissipation × θJA
- Electrical headroom
- VIN − VOUT − required dropout
The model is deliberately simple. It does not model transient thermal impedance, package-to-case interfaces, heatsinks, board spreading resistance, load duty cycle, current limiting, thermal shutdown cycling, or regulator-specific safe-operating-area behavior.
Use defensible inputs
- VIN: use the worst-case voltage at the regulator pin, not the supply label.
- Dropout: prefer the maximum at relevant load and temperature over a headline typical.
- θJA: match package, copper area, board stack, and airflow as closely as the manufacturer’s datasheet permits.
- Junction limit: use the recommended operating boundary for the exact grade when it is lower than absolute maximum.
Stop conditions
Stop if electrical headroom is negative, the estimate reaches the entered junction limit, or the design depends on a best-case typical thermal number. A positive calculator margin is permission to verify, not proof that the assembly is safe.
Choose the exact regulator
Comparing 1117-family parts? Read the AMS1117, LM1117, and TLV1117 comparison before transferring one manufacturer’s limits to another part.
Change the architecture when needed
The PCB power-tree design guide and the voltage-regulator selection surface connect this estimate to switching conversion, rail sequencing, and verified parts. Then propagate this stage and its children through the multi-rail power budget.
Common questions
What does θJA mean in this calculator?
θJA is the junction-to-ambient thermal resistance used to estimate junction temperature: ambient plus total dissipation times θJA. Match it to the exact package, copper area, board stack, and airflow as closely as the manufacturer's datasheet permits—a mismatched θJA value makes the temperature estimate meaningless.
What does the calculator's dissipation estimate include?
The calculator sums load dissipation, (VIN − VOUT) × ILOAD, and ground-current dissipation, VIN × IGND, to get total heat. It is deliberately simple: it does not model transient thermal impedance, package-to-case interfaces, heatsinks, board spreading resistance, load duty cycle, current limiting, thermal shutdown cycling, or safe-operating-area behavior.
What counts as a stop condition on this calculator?
Stop if electrical headroom—VIN minus VOUT minus required dropout—is negative, the estimate reaches the entered junction limit, or the design depends on a best-case typical thermal number. A positive calculator margin is permission to verify further, not proof that the assembly is thermally safe.
Is the thermal calculator result a sign-off for production?
No. It is an estimate, not a sign-off. θJA depends on package, copper, vias, airflow, neighboring heat sources, orientation, and the manufacturer's test board. Use the exact datasheet, worst-case tolerances, thermal measurements, and the applicable operating junction limit before releasing hardware.
Found an error? Submit a correction — we verify every correction against the manufacturer’s datasheet.