The MOSFET is a four-terminal semiconductor device used for switching and amplifying electronic signals. It comes in two basic forms, P-channel and N-channel, and two modes, depletion and enhancement. MOSFETs exhibit three operating regions - cut-off, where no current flows; ohmic or linear, where current increases with drain-source voltage; and saturation, where current reaches a maximum. MOSFETs are voltage-controlled, unipolar devices that can switch or amplify depending on their operating region.

1. Power MOSFET
Prepared by,
Mr. A. Johny Renoald M.E., Ph.D.,

2. Symbol and Structure
• The MOSFET (Metal Oxide Semiconductor Field Effect Transistor)
transistor is a semiconductor device which is widely used for switching and
amplifying electronic signals in the electronic devices
MOSFET is a four terminal device
• Source(S)
• Gate (G)
• Drain (D)
• Body (B)

3. Types
MOSFETs are available in two basic forms
P- Channel
N – Channel
• Depletion Type: The transistor requires the Gate-Source voltage (VGS) to
switch the device “OFF”. The depletion mode MOSFET is equivalent to a
“Normally Closed” switch.
• Enhancement Type: The transistor requires a Gate-Source voltage(VGS) to
switch the device “ON”. The enhancement mode MOSFET is equivalent to
a “Normally Open” switch.

4. P-Channel MOSFET

5. N-Channel MOSFET

6. MOSFET Characteristics
• MOSFETs are tri-terminal, unipolar, voltage-controlled device which form an
integral part of vast variety of electronic circuits.
• These devices can be classified into two types
Depletion-type
Enhancement-type
MOSFET exhibits three operating regions
Cut-Off Region
• Cut-off region is a region in which the MOSFET will be OFF as there will be no
current flow through it.
• In this region, MOSFET behaves like an open switch and is thus used when they
are required to function as electronic switches
Ohmic or Linear Region
• Ohmic or linear region is a region where in the current IDS increases with an
increase in the value of VDS.
• When MOSFETs are made to operate in this region, they can be used as amplifiers.

7. Saturation Region
• In saturation region device will act like a closed switch through which a
saturated value of IDS flows.
• As a result, this operating region is chosen whenever MOSFETs are
required to perform switching operations

8. • Transfer characteristics (drain-to-source current IDS versus gate-to-source
voltage VGS) of n-channel Enhancement-type MOSFET
• Current through the device will be zero until the VGS exceeds the value of
threshold voltage VT
• Under this condition, even an increase in VDS will result in no current flow
• Once VGS crosses VT, the current through the device increases with an
increase in IDS initially (Ohmic region) and then saturates to a value as
determined by the VGS (saturation region of operation)

9. Thank you