To understand Turn-on and Turn-off phenomena of the Power
MOSFET, we will assume clamped inductive switching as
it is the most widely used mode of operation. This is shown
in Fig. (4A) and Fig. (4B). A model of MOSFET is shown
with all relevant components, which play a role in turn-on
and turn-off events. As stated above, MOSFET’s Gate to
Source Capacitance CGS needs to be charged to a critical
voltage level to initiate conduction from Drain to Source. A
few words of explanation will help understand Fig. (4A)
and Fig. (4B). The clamped inductive load is being shown
by a current source with a diode D connected antiparallel
across the inductor. The MOSFET has its intrinsic internal
Gate resistance, called RGint. As described above, the inter-
junction parametric capacitances (CGS, CGD and CDS)
are shown and connected at their proper points. VDD represents
the DC Bus voltage to the Drain of the MOSFET
through the clamped inductive load. The Driver is supplied
by Vcc of value Vp and its ground is connected to the
common ground of VDD and is returned to the Source of
the MOSFET. The output from the Driver is connected to
the Gate of the MOSFET through a resistor RGext.