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I'm not sure to correctly understand the datasheet of Traco THN24 family. I read this:
Thermal impedance – Natural convection 17.6°C/W
but the DCDC is rated for 20W without de-rating (100% output power) at ambient temperature of 60 °C with natural convection and without heatsink.
This makes no sense for me, because the temperature should rise up to 20W * 17.6 °C/W = 352 °C!
Of course I'm wrong, otherwise the product cannot be used at the specified power. Where is my mistake?
The efficiency is given as a typical figure, so reduce it a little for a safety margin.
Output power: 20 W
Efficiency: 0.85
Input power = 20 W/0.85 = 23.53 W
Waste power = 23.53 W - 20 W = 3.53 W
Temperature rise = 3.53 W * 17.6 K/W = 62.1 K
Resulting case temperature at 20 °C ambient = 82 °C.
The data sheet says the maximum case temperature is 105 °C so it will work.
However I would not like a component to be that hot (e.g. it might severely reduce the life of other components near it) so I would be looking at adding a more substantial heat sink than the optional one and some forced air flow if it was going to be run at that heat dissipation.
