Cds Capacitance for ZVS Calculations

yfahmy

Hello,

I am interested in the drain source capacitance and the charge that will be moved onto and off of it during soft switching (ZVS). The data sheet for the 32120K and similar TO package FETs list Coss and Crss, which are typically subtracted to give Cds. One part I did not fully understand is the Vac of 25mV (applied to Vgs? Vds?). Does this imply this is a small signal capacitance and therefore cannot be used for the full Vds bus swing?

Or can I use the values provided so that at an 800V bus we should expect Cds ~= 100pF (fig 17) and therefore if softswitching is achieved in a two level converter that Qds ~= 80nC will be moved every switching cycle?

If it is indeed a small signal value is there a large signal value that can be provided by Wolfspeed? Or will this have to be measured in a test setup?

Thank you in advance.