Power MOSFET or Power Metal Oxide Semiconductor Field Effect Transistor is a power device that is
used in many applications due to its promising capabilities like high switching speed compare to the
regular MOSFET and it also has low gate drive power advantage.
It has two polarities :
? P channel- positive
? N channel- negative
Figure 1: Power MOSFET’s Schematic Symbols
Figure 2. N-Channel Enhancement-Mode Power MOSFET
The Power MOSFET is also known as V- MOSFET / VFET due to its vertical structure which can be
visualized on the construction of the device or its ” V” cut (as shown on the figure above). It consist of
four layers of n+, p, n,- n+ structure. The n+ source and drain terminal are separated due to the presence
of p- base region , Then the p-base region creates a P-N junction between that p base region and the
drain. In addition, the flow of current is in vertical fashion which is different from other MOSFET which
are known as the planar MOSFETS, which current flows in horizontal or planar direction.
Power MOSFET has two modes of operation which are:
A. Enhancement mode – the device is being “normally off”, it has no channel, meaning the
current from the source (S) has no way towards the drain (D) unless otherwise enhanced.
When there is no current applied then there will be nothing to flow or it will not conduct.
B. Depletion mode- the device is “normally on”, means that it doesn’t require a gate current
(Ig) to function. It’s called depletion mode because it “depletes” when we apply more
negative gate voltage than the threshold voltage -VTH or –VGS.
The power MOSFET’s are used in the power supply applications
? It can be used as a DC to DC converters
? Low voltage motor controllers
? These are widely used in the low voltage switches which are less than the 200V
Guide Book in Electronics Engineering by Ronnie B. Villamor