Skip to content

Product strategy & process Industrial design & mechanical Electronics development Prototyping & manufacturing Certification & compliance Founder advisory Electronics manufacturing Sourcing & manufacturing Supplier sourcing Production management

Mechanical engineering tools Electronics engineering tools Software engineering tools All engineering tools Downloads Hardware notes

Projects About Contact Start a Project

TOOL IDB-ELE-005

Heatsink & junction T

Desktop only

Engineering tools are available only on desktop screens.

Heatsink & junction T

Junction temperature, required heatsink thermal resistance, and safety margin for a power device.

Thermal stack J → A RSA = —

Tj vs power dissipated at chosen Rθtotal

Power dissipated W

Ambient Ta °C

Max Tj °C

Derate margin °C

R_θJC °C/W

R_θCS °C/W

Engineering notes

Thermal stack

Tj = Ta + P · (R_JC + R_CS + R_SA)
Required: R_SA ≤ (Tjmax − margin − Ta)/P − R_JC − R_CS

Sanity checks

If R_SA required is negative, even an infinite heatsink isn't enough.
Natural convection in plastic rarely beats 10–15°C/W on standard heatsinks.

Result

Live

We would like to use Google Analytics to see which pages are actually useful. It stores a cookie in your browser and sends your IP address to Google. We measure nothing unless you say yes.

How we use data

Ideambox Contact Privacy Policy TermsIf the required heatsink comes out impossible, the reference has the LDO-vs-buck rule that stops making the heat. Electronics and PCB design → Staff login