This project report comprises of a mosfet gate driver circuit as well as an application for the same - Automatic Exhaust Fan using an arduino.

1. [Title Here, up to 12 Words, on One to Two Lines]
Sankarshan Durgaprasad – PES1201700495
PES University
Power Electronics Open Ended

2. Abstract
To create an efficient and instantaneous
system that detects the presence of
smoke / gas leaks in the environment and
expels the same. With the help of a power
electronic device preferably MOSFET as it
provides great amount of efficiency while
also having an extremely high switching
speed. This helps in alerting and taking
the necessary action immediately.
MOSFETS
Metal Oxide Silicon Field Effect Transistor
is abbreviated as MOSFET. It is merely a
unipolar transistor and used as an
electronic switch and to amplify electronic
signals. The device has three terminals
consisting of a source, gate and drain.
Apart from these terminals there is a
substrate generally called the body which
is always connected to the source
terminal for practical applications.
MOSFET Characteristics
MOSFET is seen to exhibit three operating
regions.
1. 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.
2. 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.
3. Saturation Region
In saturation region, the MOSFETs
have their IDS constant inspite of
an increase in VDS and occurs once
VDS exceeds the value of pinch-
off voltage VP. Under this
condition, the 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.
Types of MOSFETs
 Enhancements type MOSFET
 Depletion type MOSFET
Depletion-mode MOSFET,
which is less common than the
enhancement mode types is normally
switched “ON” (conducting) without the
application of a gate bias voltage. That is
the channel conducts
when VGS = 0 making it a “normally-
closed” device.
Enhancement-mode MOSFET or
eMOSFET, is the reverse of the depletion-
mode type. Here the conducting channel

3. is lightly doped or even undoped making it
non-conductive. This results in the device
being normally “OFF” (non-conducting)
when the gate bias voltage, VGS is equal to
zero.
Applications of MOSFETS
 MOSFETs areused in digital integrated
circuits,such as microprocessors.
 Used in calculators.
 Used in memories and in logic CMOS gates.
 Used as analogswitches.
 Used as amplifiers.
 Used in the applicationsof power
electronics and switch mode power
supplies.
 MOSFETs areused as oscillators in radio
systems.
 Used in automobilesound systems and in
sound reinforcement systems.
In this project, we will be focusing on
N channel enhancement MOSFET.
Other component used - Optocoupler
An Optocoupler, is an electronic
components that interconnects two
separate electrical circuits by means of a
light sensitive optical interface. In this
project we will be using a PC 817
optocoupler which is a 4 terminal device.
On providing 5 V between the anode and
cathode the IR diode turns on hence
emitting IR rays, this results in the base of
the phototransistor getting triggered and
hence the transistor turns on. The desired
voltage is given to terminal 4 and the
output is obtained at terminal 3.
MQ2 Sensor
MO2 sensor is a sensor that can detect
both LPG and smoke. It can product both
Analog output as well and Digital output.
It works on the principle of voltage
divider. When the sensor detects
smoke/LPG it gives a high voltage output
whereas in its absence gives 0 V output.
Cut off Characteristics

4. Saturation Characteristics
Circuit Diagram
Working
On State ( Saturation )
In the presence of smoke/LPG the MQ2
sensor produces analog outputs. If the
analog outputs received by the Arduino is
greater than the thresh hold that has
been pre-defined the Arduino produces 5
v output. The 5 V given by the Arduino
triggers the optocoupler on, on doing so
12 V trigger voltage is given to the gate
terminal of the MOSFET.
At this state Vth < Vgs of the mosfet.
Hence the MOSFET turns on this results in
Running the mosfet
Off State ( cut-off )
In the absence of smoke/LPG there is no
analog output received by the Arduino
hence 5v is not given by the Arduino.
Therefore, the optocoupler is turned off.
This means that there is no Triggering
voltage given to the MOSFET. Hence as
discussed earlier for an enhancement type
MOSFET Vgs > Vth for the MOSFET to be
on.

5. Numerically finding out the power
dissipated in the MOSFET.
Considering the MOTOR ( 12 V , 12 W ) to
be fully on,
P = V * Id
Id = 12 W / 12 V = 1 A
Rds = 0.077 ohm ( from data sheet )
Power dissipated at the MOSFET
= Id^2 * Rds
= 1*1 * 0.077 A
= 0.077 W
When using the MOSFET as a switch to
control DC motors or electrical loads with
high inrush currents the “ON” Channel
resistance ( RDS(on) ) between the drain and
the source is very important. For example,
MOSFETs that control DC motors, are
subjected to a high in-rush current when
the motor first begins to rotate, because
the motors starting current is only limited
by the very low resistance value of the
motors windings.
As the basic power relationship
is: P = I2*R, then a high RDS(on) channel
resistance value would simply result in
large amounts of power being dissipated
and wasted within the MOSFET itself
resulting in an excessive temperature rise,
which if not controlled could result in the
MOSFET becoming very hot and damaged
due to a thermal overload.
A lower RDS(on) value for the channel
resistance is also a desirable parameter as
it helps to reduce the channels effective
saturation voltage ( VDS(sat) = ID*RDS(on) )
across the MOSFET and will therefore
operate at a cooler temperature. Power
MOSFETs generally have a RDS(on) value of
less than 0.01Ω which allows them to run
cooler, extending their operational life
span.
When using a MOSFET or any type of field
effect transistor for that matter as a solid-
state switching device it is always
advisable to select ones that have a very
low RDS(on) value or at least mount them
onto a suitable heatsink to help reduce
any thermal runaway and damage.