## FET CHARACTERISTICS

AIM

To plot the characteristics of FET (BFW 10) and to find the following parameters

1. Drain dynamic resistance

2. Mutual conductance

3. Amplification factor

COMPONENTS AND EQUIPMENTS REQUIRED

1. FET

2. Ammeter

3. Voltmeter

4. DC supply

CIRCUIT DIAGRAM

THEORY

FET is the Field Effect Transistor. It is 3 terminal voltage controlled device. It’s terminals are drain, source and gate. Gate is the controlling terminal. Consider an n channel device. The gate (p material) is diffused. At zero gate voltage there is no reverse voltage at the channel. So as Vds (drain source voltage) increases current Ids also increases linearly. As the voltage is increased, at a particular voltage, pinch off occurs .This voltage is known as pinch off voltage. After pinch off drain current remains stationary .If we apply a gate voltage (negative voltage) the pinch ff occurs early.

Advantages of FET over BJT are:

a) No minority carriers

b) High input impedance

c)  It is a voltage controlled device

d) Better thermal stability

PROCEDURE

1. Identify the leads of FET

2. Make the circuit as given.

3. Keeping the gate voltage at 0 V, vary the drain source voltage and observe the current values.

4. Now make the gate voltage at any value (say -1 V) .Vary the drain source voltage and observe the current values.

5.  Plot the graph of static characteristics

6. Now make drain source voltage at a value (say 10 V) and take the ammeter                                                                                                                                                                                                                                                      readings by varying the gate voltage.

7. Take the readings for other drain to source voltages.

8. Plot the graph (transfer characteristics)

9. Find the drain dynamic resistance from static characteristics and Mutual conductance from transfer characteristics by taking the slopes

10. Find the amplification factor by multiplying the above two values

OBSERVATIONS

1.      To plot the static characteristics

.Vgs=0 V                                     Vgs= -1 V                               Vgs= -2V

 Vds(volts) Id(mA) Vds Id Vds Id

2.      To plot the transfer characteristics

Vds=10 V                                                         Vds= 20 V

 Vgs(volts) Id(mA) Vgs Id

GRAPH OF STATIC CHARACTERISTICS

TRANSFER CHARACTERISTICS

CALCULATIONS

Drain resistance, rd=∆Vds/∆ Ids (take the slope of graph)

Mutual conductance, gm=∆Id/∆Vgs

Gain, μ=gm rd

RESULT

Characteristics of FET were plotted.

Drain dynamic resistance=…………..

Mutual conductance=………………..

Amplification factor=………………..

SAMPLE VIVA QUESTIONS

1. What are the advantages of FET over BJT?

a) No minority carriers

b) High input impedance

c) It is a voltage controlled device

d) Better thermal stability

3.      Define pinch off voltage

See theory

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### 8 Responses to “FET CHARACTERISTICS”

• ravindra jallepalli says:

please mention some of the applications of the given circuits

• ravindra jallepalli says:

• vijay says:

i cannot able to view the circuit diagrams in electronic circuit lab link, anybody kindly help me in this issue, iam using google chrome, i tried in mozilla firefox also,

• rupali says:

whats d procedure to identify the leads of fet?

• swamy says:

fisrt observe the natch on the fet from the natch anti clock wise direction
source,gate anddrain orderly.

• rutuja ghalle says: