capacitancemosfetparasitic-capacitance
I need to use the best model for the MOSFET in my circuit I'm simulation on PSIM, the MOSFET is Si4108-TI-GE3.
But I am not given the parasitic capacitance values (Cgs Cds Cdg), I am only given this:
I think I should use Q=CU, but I don't see how to use Q=CU for Cds since I only have Total gate charge and I don't know if that is the drain-source charge. How do I calculate the necessary parasitic capacitance values?
\$C_{rss}\$ is not measured by putting a capacitance meter between gate and drain, and leaving the source open.
It is inferred from the ramping behaviour, which is largely controlled by the Miller capacitance, the gate current needed to charge up the \$C_{rss}\$ capacitor, when the drain is slewing in voltage.
This is equivalent to making a three-terminal capacitance measurement across gate and drain, with a guard terminal on the source. This is capable of measuring all three capacitors in that diagram independently, even for the very different values that are shown.
Though it has been more than one year since you ask this question, I think it might be helpful to leave a comment here in case someone has the same problem (like myself in twenty minutes ago). I find these values could be find in the log files named "yourschematicname.log" in the folder storing your schematics. This holds true for both BJT and CMOS. And I am sure that they vary when you modify the DC bias point.
Parasitic capacitances of BJT:
Parasitic capacitances of NMOS:
Best Answer
Read the data sheet: -
Ciss is gate-source capacitance. You should be able to work out the other two.