Power Dissipation: 1.5 V, 0.3 A, θ=200 °C/W
A small SMD component with 1.5 V and 0.3 A dissipates 0.45 W, giving a 90 °C junction rise at θJA=200 °C/W.
How to use this tool
- Enter voltage across component, current through component, resistance and thermal resistance (θ_ja) in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your power dissipated and the full breakdown beneath it.
Small SOT-23 packages have very high thermal resistance; even 0.45 W can cause a significant temperature rise in tiny SMD components.
Frequently asked questions
- What is thermal resistance (θ_JA)?
- It is the resistance to heat flow from the component junction (hottest point) to the ambient air, in °C/W. A small IC might have θ_JA = 100 °C/W; a power transistor on a heatsink might be 5 °C/W.
- How do I derate a component for safety?
- Most manufacturers recommend derating to 50–70% of the maximum rated power at 25 °C. Check the derating curve in the datasheet for operation at elevated ambient temperatures.