THERMAL MANAGEMENT
Thermal Management
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Thermal Resistance
Thermal resistance is way of modelling the thermal behaviour of an object in a way analogous to calculating the current through a resistor by measuring it’s voltage.
The equation is given by:
where:
\( P_D \) = Power dissipated by device (\( W \))
\( \Delta T \) = Change in temperature between both end-points
\( \sum R_{\theta} \) = The sum of thermal resistances over which \( \Delta T \) exists
Which is usually expanded (and used) as:
If there is a heatsink involved, a new term is added:
A diagram showing how thermal resistance works. Image from http://www.aavid.com/sites/default/files/products/boardlevel/aavid-standard-heatsinks.pdf.
An analogy to electrical resistance…
The analogy of thermal resistance to electrical resistance. Image from http://www.vishay.com/docs/28705/mc_pro.pdf.
Inaccuracies In The Thermal Resistance Model
- Thermal resistances assume a linear relationship between temperature and heat flow. This is only a first-order approximation.
List Of Component Package Thermal Resistances
See the Component Packages page. This has many of the common component packages and their thermal resistances.
Below is a condensed list of experimentally found internal thermal resistances (junction-to-case).
Experimentally determined values for the internal thermal resistance (junction-to-case) for various sized SMD resistors. Image from http://www.vishay.com/docs/28705/mc_pro.pdf.
Authors
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