thermal model T-Type

Question

Hi!
I’m trying to build a thermal model of the single leg of a T-Type, consisting of 4 MOSFETs+diodes. When I try to run, I get that in Sub4 the graph has a negative peak before reaching stationat conditions, even if, when I record the MOSFET+diode temperature, this is always increasing.
I'm leaving the model built below, together with the XML for the thermal model.
I’ve only been using PLECS for a short time and I can’t figure the mistake out. If someone could help me, it would be very welcome!
Thank you very much

Comments

Hello, can you also include the XML file for SCT020H120G3AG that you are using in your model?

Answer 1

Hello, I was able to reproduce what you mentioned. Here the initial power flow in Device 4 goes to charge up the large junction capacitance you assigned (1 J/K, to all device junctions) before then flowing out to ambient. This is just the nature of your circuit and its parameters. In this case I might suggest that you either use a much lower thermal capacitance value or import the transient thermal impedance curve from the datasheet (Figure 2 - single pulse) into the Thermal Editor's Thermal chain tab directly (and then not use the external Cth_j and Rth_jc values). When I imported this curve you can see the order of magnitude of the capacitance values assigned:

From a quick simulation this then shows a positive-only transient heat flow out from device 4's junction.