Study of transfer characteristics and output characteristics of Junction Field Effect Transistor (JFET)

Objective:

To Plot the characteristics of FET & determine rd, gm, μ, IDSS,VP. 

Theory:

FET is a voltage operated device. It has got 3 terminals. They are Source, Drain & Gate. When the gate is biased negative with respect to the source, the pn junctions are reverse biased & depletion regions are formed. The channel is more lightly doped than the p type gate, so the depletion regions penetrate deeply in to the channel. The result is that the channel is narrowed, its resistance is increased, & ID is reduced. When the negative bias voltage is further increased, the depletion regions meet at the center& ID is cutoff completely.

Apparatus Used:

Circuit Diagram:

Procedure: 

  • Transfer Characteristics:
  1. Connect the circuit as per the circuit diagram.
  2. Set the drain voltage VDS = 5 V.
  3. Vary the gate voltage VGS in steps of 1V & note down the corresponding ID.
  4. Repeat the same procedure for VDS = 10V.

Plot the graph VGS Vs ID for constant VDS.

  • Drain Characteristics:
  1. Connect the circuit as per the circuit diagram.
  2. Set the gate voltage VGS = 0V.
  3. Vary VDS in steps of 1 V & note down the corresponding ID.
  4. Repeat the same procedure for VGS = -1V.
  5. Plot the graph VDS Vs ID for constant VGS. 

Drain Resistance     rd = ∆VDS/ ∆IDfor Constant VGS 

Transconductance   gm = ∆ID/ ∆VGS for Constant VDS 

Amplification factor  μ=rd . gm 

Observation Table:

  • Transfer Characteristics:

For VDS=5V

For VDS=10V

  • Output Characteristics:

For VGS=0V

For VGS= -1V

Result and Analysis:

Conclusion: Should follow result in conformation with theory.

 

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