Inconsistency Between C3M0120090J datasheet and SpeedFit 2.0 Design Simulator for Switching Loss Cal

Efecan

Hello,

As a company we use your SpeedFit 2.0 Design Simulator in Wolfspeed website. While simulating, we encounter with following problem.

Here, we use C3M0120090J SiC Mosfet in the circuit. we take gate resistance(Rg) of the transistor as 10 ohm in the simulation. Also, we enter below inputs for simulation in 25 Celcius. (400V, 15A)

After input stage, we get following results at the end of simulation. Switching power loss for all four SiC Mosfets is around 21W as you can observe.

When we look at the graph from C3M0120090J SiC Mosfet datasheet, we see that when Rg=10 ohm switching energy loss is around 50 uJ for one transistor. When it is multiplied by 250kHz switching frequency, 12,5W switching power loss is obtained for one transistor. As a result, for H-bridge circuit with 4 transistor above, total switching power loss should correspond to 50W according to datasheet. However, it is obtained as nearly 21W in the simulation. We wonder why inconsistency occurs in that situation. If you have any opinion for that problem can you explain?

Thank you for your consideration.

ZMiller

Hi,

I'm currently investigating your question and I will provide a follow-up as soon as I have a resolution for this.

Thanks,

Zack

ZMiller

Hi,

I believe that the losses you are seeing in Speedfit are a more accurate representation of the switching losses you would expect to see in real operation. Using the datasheet, the calculation assumes a current through the MOSFET of 15A for each switching cycle and does not factor in the impact of the controller on the switching cycle - namely, the lack of switching that occurs as the output voltage waveform approaches the bus voltage level.

Since Speedfit performs the switching loss calculation at each switching event, it is creating a more accurate switching loss profile by accounting for the variation in current during each switching event.

Please let me know if you have any further questions!

Thanks,

Zack

AAnders

Hi, I hope that this answered your question. I will close this discussion for now but if you have a follow up question, please "Start a New Discussion" and we would be glad to support you further.