Documentation

Heat Sink Calculator

2 min read

This is a calculator based around the calculation of thermal resistance in a heat sink. It can be used to help with the selection of a suitable heat sink for a transistor or other semiconductor device that is mounted in a case that is then mounted on the heat sink.

Shortcuts

Default Keys: None

Default Menu: Utilities

Command: Design Calculators

Locating this option

Available from: Utilities menu > Design Calculators option

Using this option

This calculator is on a tab on the Design Calculators dialog, available from the Utilities menu. The following dialog appears when the Heat Sink tab is selected.

This calculator uses the basic formula:

Total Thermal Resistance = Temperature Rise / Device Power

The Temperature Rise is the rise from the ambient air temperature to the maximum device temperature, often called the junction temperature of the device.

The Total Thermal Resistance is made up the following parts:

  1. The “Junction to Case” thermal resistance for the device.

    This figure can usually be obtained for the device from the manufacturers data, or can be calculated from the device case temperature.

  2. The “Case to Sink” thermal resistance of the thermal interface material between the device and the heat sink.

    This is normally either a layer of thermal paste (thermal compound):

    or more likely an insulating washer with thermal paste either side:

  3. The thermal resistance between the heat sink base and the ambient air.

Using the dialog

First select the value you want calculated using the radio button on the appropriate section.

  • Device Power
  • Temperature Rise
  • Heat Sink Thermal Resistance

The value being calculated will become a read only box. Enter the values in the other sections to produce the result. The result will be blank if not all the required values are entered.

Once you have calculated the required result, you can switch to the Conversion Calculator tab to see the result in engineering or scientific notation.

NOTE: These calculations are approximations, and should not be used if a high degree of accuracy is required.

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