Mosfet ,types, working, modes of operation ,diagram ,applications.

1. MADHAV INSTITUTE OF TECHONOLOGY AND SCIENCE
Submitted to,
Prof. D.K Parsedia
Prof. Ranbir Tyagi
Submitted by,
Shubham Yadav
Mahima Shakya
Akhil Rojouria
Asit Rajouria
Virendra Rohitas

2. MOSFETs
Metal-Oxide-Semiconductor
Field Effect Transistors

3. 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. The MOSFET is a core of integrated circuit and
it can be designed and fabricated in a single chip because of these very small
sizes. The MOSFET is a four terminal device with source(S), gate (G), drain (D)
and body (B) terminals. The body of the MOSFET is frequently connected to the
source terminal so making it a three terminal device like field effect transistor.
The MOSFET is very far the most common transistor and can be used in both
analog and digital circuits. The conductivity (or resistivity) of the path between
two contacts, the source and the drain, is altered by the voltage applied to the
gate.
Device is also known as a voltage controlled resistor.
AN INTRODUCTION TO MOSFET -

4. The Source and Drain are separated about 10-20 micrometer. A thin layer
( 1000 – 2000 A), layer of insulating silicone dioxide (SiO2) is grown over the
surface of structure.

5. The P- Channel MOSFET has a P- Channel region between source and drain. It is
a four terminal device such as gate, drain, source, body. The drain and source
are heavily doped p+ region and the body or substrate is n-type. The flow of
current is positively charged holes. When we apply the negative gate voltage,
the electrons present under the oxide layer with are pushed downward into the
substrate with a repulsive force. The depletion region populated by the bound
positive charges which are associated with the donor atoms. The negative gate
voltage also attracts holes from p+ source and drain region into the channel
region.
TYPES OF MOSFET -
1) p-type

7. N type –
The N-Channel MOSFET has a N- channel region between source and
drain It is a four terminal device such as gate, drain , source , body.
This type of MOSFET the drain and source are heavily doped n+ region
and the substrate or body is P- type. The current flows due to the
negatively charged electrons. When we apply the positive gate
voltage the holes present under the oxide layer pushed downward
into the substrate with a repulsive force. The depletion region is
populated by the bound negative charges which are associated with
the acceptor atoms. The electrons reach channel is formed. The
positive voltage also attracts electrons from the n+ source and drain
regions into the channel. Now, if a voltage is applied between the
drain and source the current flows freely between the source and
drain and the gate voltage controls the electrons in the channel

9. MODES OF OPERATION-
Enhancement mode
 Also known as Normally Off transistors.
 A voltage must be applied to the gate of
the transistor, at least equal to the threshold
voltage, to create a conduction path
between the source and the drain of the
transistor before current can flow between
the source and drain.
Depletion mode
 Also known as Normally On transistors.
 A voltage must be applied to the gate of the
transistor, at least equal to the threshold
voltage, to destroy a conduction path
between the source and the drain of the
transistor to prevent current from flowing
between the source and drain.

10. Enhancement Mode -
Symbols for n channel
Enhancement Mode MOSFET
Symbols for p channel
Enhancement Mode MOSFET

11. Depletion mode -
Symbols for n channel
Depletion Mode MOSFET
Symbols for p channel
Depletion Mode MOSFET

13. APPLICATIONS-

14. Enhancement n-channel MOSFETs
are in their OFF state when no gate-
to-source voltage is applied. However
when biased with a suitable positive
voltage, it starts to conduct allowing
the flow of drain current through it.
This current is seen to increase in
magnitude as the bias voltage
increases which in turn leads to the
increase in output voltage. Thus the
MOSFETs serve as amplifiers .
MOSFET amplifiers are used in radio-
frequency applications and in sound
systems.
AS AN AMPLIFIER -

15. The switching action of MOSFETs can be
exploited to design chopper circuits as
shown by Figure 4. Here the DC voltage,
VDC is converted into AC voltage with the
same amplitude level, VAC by biasing the
MOSFET using a square voltage waveform
between its gate and source terminals. This
causes the MOSFETs to operate in cut-off
and saturation regions in alternate cycles.
AS CHOPPER -

16. Depletion type MOSFETs in source-
follower configuration are used in
linear voltage regulator circuits as
pass transistors (Figure 5). Here the
source voltage, VL follows the gate
voltage, VG minus the gate-to-source
voltage, VGS. Further VGS increases
with an increase in the drain current,
ID. Thus if the gate voltage is fixed,
then the source voltage will reduce
as the load current, IL increases.
AS VOLTAGE REGULATOR -

17. NUMERICALS -

21. THANKYOU