Tuesday, 28 April 2015

MOSFET Miller effect: length of the gate voltage flat area


As per Miller effect the gate voltage stops to grow at the threshold level until some certain moment:


enter image description here


This can be explained as the drain to gate capacitance drives current through the gate. However - it is clearly can be seen on the picture that the flat area goes far beyond the moment Vds drops to the minimum. I could suppose that Vgs should grow further after 35 nC or so. But it stays still until 85 nC or so.


It is clear that dU/dt (which is the most important part in the equation of the capacitor current) much lower after 35 nC or so.


I checked several datasheets from different manufacturers but the picture is roughly the same.


So the question is:


What holds the gate for extra 50 nC (if we take this TK31V60W5 Toshiba MOSFET as the example)?





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