The switching device must be sufficiently cooled so that the junction temperature does not exceed the required values: usually 125 or 150°C (this value depends on the power components) and so that the temperature of the heatsink does not exceed 90 or 100°C.
The heatsink can be determined either by calculation (see technical note - pages 4 to 6) or directly from the curves provided by celduc.
The type of heatsink to use can be determined by the switched current and the ambient temperature.
Operating mode of the above curves:
1- identify the current to switch on the abscissa of the left-hand curve
2- plot a vertical line from the above point up to the curve (1)
3- from the obtained point, a horizontal line is plotted to the right-hand curve (2)
4- identify the ambient temperature on the abscissa of the right-hand curve
5- plot a vertical line from this point until you reach the horizontal line previously plotted (3)
6- this point determines the type of heatsink to use
7- select the heatsink corresponding to the curve located above this point. In this example 1.2°/W (4)
You can see that for a 1.2°/W, 6A heatsink, the ambient temperature should not exceed 54°C (8) (9)
And a 1.2°/W heatsink in a 38°C ambient temperature, the maximum current can reach up to 8A (5) (6) (7)
To have access to our complete range of heatsinks - click here
Also refer to:
Thermal Pads or Thermal Paste – Differences and Advantages