I am calculating the MOSFET Switching losses in the PLECS with the thermal wizard using the formula panel. I wrote simple formula as I don’t have any switching losses graph from the vendor. My question is, Do I need to provide voltage and current value or Software will take data automatically?

If Software is taking data automatically, I am not getting any switching losses (Very minimal) which I think is wrong compare to analytical calculation.

Basically How does the formula method in the themal wizard works if the Graphs ae not provided by the vendors?

Firstly, I would like to point out that in the absence of a sufficiently detailed data sheet or thermal model from the vendor you run the risk of generating less meaningful (more bluntly, incorrect) simulation results. Simple formulas will neglect the temperature dependence of the loss characteristics and other non-linear characteristics, which of course can greatly impact the results. However, in academic settings or if there is a complete lack of data, the approach outlined below could be helpful.

Attached is a basic example using formulas from Chapter 4 of Erickson’s “Fundamentals of Power Electronics”. The v, i, and T values are the voltages, currents, and temperature of the switch during a given switching transition. The t_r, t_f, Qrr, and RdsOn variables are in the “variables” tab of the thermal description. Then you can then refer to them in the formulas. Another resource is the Infineon App Note titled “Mosfet power losses calculation using the data-sheet parameters”.

bucktherm.zip (212 KB)

Hello Bryan Lieblick,

Thank you for the detailed explaination and the sample model. It is really helpful.