Aim :
To study the characteristics of a field-effect transistor (FET) and its use as a voltage-variable resistance (VVR).
Apparatus :
n- channel FET, two dc power supplies, milliametres, resistance, voltmeters, connecting wires.
Formula :
Circuit Diagram :
Procedure :
Credit – Sadhish Prabhu
- Connect the circuit for obtaining the drain curves (ID – VDS characteristics) as shown in figure.
- Keep VGS = 0V. Vary VDS from 0 to 10 V in suitable steps and note corresponding values of ID. In order to get ohmic region characteristics VDS can be varied as 0.0V, 0.2V, 0.4V, 0.6V, 0.8V, 1.0V, 2.0V, 3.0V, ……….10V.
- Repeat the above procedure keeping VGS = -0.5V, -1.0V and -1.5V.
- Plot ID against VDS (drain curve). Show the ohmic and active regions of the characteristics curves.
- Determine the pinch-off voltage (VP) from the graph (for VGS = 0V).
- Obtain the values of RDS of JFET operation in the ohmic region. Tabulate the values of RDS against VGS. Comment on the result.
- Now, connect the circuit for transconductance curve (ID – VGS characteristics). Keep VDS = 10V. Observe IDSS, when VGS = 0V. Vary VGS from 0V downwards through the negative values till ID tends to zero.
- Plot ID against VGS (transconductance curve). Note down VGS(OFF) from the graph.
- Calculate gmo from the graph using the mirror when IDSS=0.
- Calculate VP from the formula. Compare the values of VP obtained from drain characteristics and from calculation.
Observation :
Viva Question and Answers [FAQ] :
1. What is JFET?
Ans : Junction Field Effect Transistor
2. What is aim of this Experiment?
Ans : Study the characteristics of a field-effect transistor (FET) and its use as a voltage-variable resistance (VVR).
3. What is apparatus for this experiment?
Ans : n- channel FET, two dc power supplies, milliametres, resistance, voltmeters, connecting wires.
4. Write formula for drain current?
Ans : Check formula below the apparatus section of this post.
5. What is nature of graph for drain curve?
Ans : Voltage verses Current.