To study and draw the characteristics of FET in common source configuration

Jun 23 2023

Aim

To study and draw the characteristics of FET in common source configuration.

Apparatus Required:

Power supply, FET characteristic Kit, connecting leads, two Multimeters.

Brief Theory:

A FET is a three terminal semiconductor device in which current conduction is by one type of carries & is controlled by the effect of electric field. There are two types of FET namely JFET & MOSFET. Again, a JFET can either have N-channel or P-channel. A N-channel JFET has a N-type semiconductor bar, the two ends of which make the Drain & source terminal. On the two sides of this bar, P-N junction is made. This P region makes gate. Usually, these two gates are connected Together to form a single gate .The gate is given a –ve bias w.r.t source. The Drain is given +ve potential w.r.t source.

Circuit Diagram:

Procedure:

Connect the circuit as per the circuit diagram

Input characteristics

Keep drain-source voltage constant
Vary gate-source voltage in steps and note down drain current
Readings are tabulated and graph is drawn

Output characteristics

Keep gate-source voltage constant
Vary drain-source voltage in steps and note down drain current.
Readings are tabulated and graph is drawn

Observation Table:

S. No	I/P at const. VDS/VGS (V)/ID (mA)	O/P at const. VGS/VDS (V)//ID (mA)
1
2
3
4
5
6
7
8
9
10
11
12
13
14

Precautions:

Connections should be tight
Handle the equipment’s with care

Result:Input and output characteristics is obtained.

Quiz:

Q.No	Question	Answers
1	Define FET?	The field effect transistor is a semi-conductor device which depends for its operation on the control of current by an electric field.
2	How many types of FET’s are there?	Two types (a) Junction field effect transistor (JFET). (b) Metal Oxide Semiconductor FET(MOSFET)
3	Write advantages of FET over conventional Transistor?	Advantages are (a) Thermal stability. (b) Immunity to radiation (c) High input impedance.
4	Write one disadvantage of FET?	Main disadvantage is relatively small ‘Gain- Band Width ‘product.
5	Define Drain resistance?	Drain resistance can be defined as ratio of drain to source voltage to drain current.
6	Define Tran conductance?	Tran conductance can be defined as ratio of drain current to gate to source voltage.
7	Define transfer characteristic of FET?	The curve drawn between drain current and gate- source voltage for a given value of drain-source voltage.
8	Write applications of a FET?	Applications of FET are(A)Low noise amplifier (B) Buffer amplifier(C) Cascade amplifier (D) Analog switch (E)Chopper
9	How is Drain current controlled in JFET?	In JFET drain current is controlled by controlling the reverse bias given to its base.
10	Define pinch-off voltage?	The value of drain-source voltage at which channel is pinched off (i.e. all the free charges from the channel are removed) is called pinch-off voltage.