Turn-On Losses at negative current using SiC (NVH4L018N0755C1)

[djdadzie]

I want to find the turn-on losses of this device (NVH4L018N0755C1) in a buck converter. I am operating the converter with some minimum negative current (from -1A to - 20 A). Theoretically, I expect that this negative current will flow through the body diode briefly, and then, the MOSFET would turn on. However, the turn-on losses of the device are predicted to be 0 W by the thermal model.

Analysing the thermal model in the image attached, there is no turn-on loss information below 0 A. Also, the equation only calculates the turn-on loss when (i > 0).

What modifications can I make to this model to estimate the turn-on losses when there is a negative current? Can I copy the tabular information for the positive current and use it for the negative current? eg: If at 40 A, the Energy is 3.4 uJ can I make it -40 A, E = -3.4 uJ?

[Bryan_Lieblick]

When the MOSFET turns on due to negative current that commutates through the body diode, this is a soft switching or ZVS as the gate is closed with zero voltage once the diode is conducting. The losses in this case will be very small, and this model assumes that the ZVS losses are zero which is a much better approximation than your proposed approach. onsemi also offers a tool to better characterize the devices under soft switching, but it requires quite a bit of application specific data to generate this custom model. You can access the tool here.