Encapsulated electronics

[Winsu]

Hi All,

I have a question related to an NTC resistor inside an encapsulation. The NTC is used for a thermal foldback system in a converter. The NTC triggers the system to reduce the current of the system when the NTC is at 75°C without the encapsulation. When the encapsulation is covering all the electronics (including the NTC) the thermal foldback system will work the same way?. I mean, the NTC will get at 75°C in the same way it does without the encapsulation? or the output current will have to rise more to achieve a 75°C at the NTC?.

or better said, will the NTC needs more time to reach the 75°C as the encapsulant will be taking the heat away?

 

[betwixt]

For any given point (the location of the NTC) there is a 'flow' of heat energy in and a flow out, the difference results in rise or fall of temperature.
The unknown here is how the encapsulant carries the heat, if it insulates and fills a gap between the heat source and NTC, and the heat conducted away remains the same, there will be a delay in temperature rise but it will eventually stabilize. If the encapsulant carries heat away faster than it arrives, the temperature will always be sensed as too low. Ambient temperature, distances and surface area all play a part in the effect.

You can see there are many variables involved here. There is no simple calculation and I think I can speak for us more experienced engineers in saying some experimentation is needed.

Brian.