To Study and Draw the Characteristics of FET in Common Drain Configuration

Aim

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

Apparatus Required:

Power supply, FET charact. 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. Drain is Common In In input and output.

Circuit Diagram:

Procedure:

(a) Connect the circuit as per the circuit diagram

Input characteristics

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

Output characteristics

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

Observation Table:

Precaution:

1. Connections should be tight
2. Handle the equipment’s with care

Result:Input and output characteristics is obtained.

Quiz/Answers:

Q1:Which is the common log in common drain FET amplifier Between input and output.

A1:Drain leg is common between input and output.

Q2:Define Pinch off voltage.

A2: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

Q3:Write advantages of FET over conventional Transistor.

A3:Advantages are (a) Thermal stability. (b) Immunity to radiation.(c)High input impedance.

Q4:How much is the gain of common drain FET amplifier?

A4:Gain of common drain amplifier is less than unity.

Q5:Define Drain resistance.

A5:Drain resistance can be defined as ratio of drain to source voltage to drain current.

Q6:Define Tran conductance.

A6:Tran conductance can be defined as ratio of drain current to gate to source voltage