LDO Thermal Calculator
Linear Regulators (LDOs) are inefficient by design—they drop excess voltage by dissipating it as heat. This makes Power Dissipation (PD) and Junction Temperature (TJ) critical design factors.
Use this calculator to verify if your LDO will survive its operating conditions. It calculates the temperature rise based on the Thermal Resistance (θJA) of your package (e.g., SOT-23, TO-220) and warns you if a heatsink is required.
Operating Conditions
InputThermal Specs & Package
SpecsPerformance Analysis
ResultLDO Thermal Design Guide
Power Dissipation (PD)
This is the heat the LDO must get rid of. It is caused by the voltage difference between input and output.
PD = (Vin – Vout) × Iload
Thermal Resistance (θJA)
Theta-JA measures how hard it is for heat to escape the chip into the air. Lower numbers are better.
- SOT-23: High resistance (~200°C/W). Gets hot fast.
- TO-220: Low resistance (~65°C/W). Good for high power.
Junction Temperature (TJ)
The internal temperature of the silicon die. If this exceeds 125°C or 150°C (depending on the datasheet), the chip will shut down or burn out.
TJ = Tamb + (PD × θJA)
Dropout Voltage
The minimum voltage difference required between Input and Output for the LDO to work. If Vin drops below (Vout + Vdo), the output will sag.
How to Use This Calculator
Enter Operating Conditions
Input your source voltage (Vin), target voltage (Vout), and the maximum current your load will draw. The tool will instantly check for dropout errors.
Select Package / Thermal Specs
Find the θJA value in your LDO’s datasheet (usually Page 3 or 4). Or, click the preset buttons (SOT-23, TO-220) to estimate.
Verify Safety
Look at the Junction Temp result. If it turns RED, you must add a heatsink, increase PCB copper area, or switch to a Buck Converter.
Frequently Asked Questions
How do I lower the LDO temperature?
You can use a larger package (like TO-220), increase the copper area on your PCB connected to the ground tab, add a heatsink, or reduce the input voltage to minimize the voltage drop.
What happens if Vin is too close to Vout?
If the difference (Headroom) is less than the Dropout Voltage (Vdo), the LDO enters “Dropout Mode.” It acts like a resistor, and the output voltage will start to follow the input voltage down, failing to regulate.
When should I use a Switching Regulator instead?
If your efficiency is below 70% or your power dissipation is > 1-2 Watts, a Switching Regulator (Buck Converter) is usually better. LDOs are best for low noise and low power applications.