Junction Field Effect Transistor (JFET) Lecture Notes

Introduction to JFET

• Discussing the working of Junction Field Effect Transistor (JFET).

Control Voltage

• Control voltage: Vgs (Gate to Source Voltage).
• Vgs = 0 when there is no potential difference.

Channel Structure

• JFET has a highly doped P-type region.
• The channel is formed internally and connected to the potential.

Terminal Connections

• Drain Terminal: Connected to positive voltage (Vdd).
• Source Terminal: At zero potential.
• Voltage Vds = Voltage between Drain and Source.

Current Flow

• Current flows from Drain to Source through the JFET.
• Electrons move from Source to Drain.
• Current direction is opposite to electron flow (from Drain to Source).

Voltage Distribution

• Applying 2 volts at the Drain results in:
  • Source at 0V, causing Vds to be effectively 1V at the midpoint.
• As Vds increases, it eventually reaches a critical voltage called Vp (Pinch Off Voltage).

Pinch Off Condition

• When Vds reaches Vp, the channel enters a state called the pinch-off condition.
• Increased Vds leads to increasing depletion region.
• High current density causes pinch-off condition.

Current Characteristics

• The maximum current value in JFET is denoted as Idss (Drain Current at pinch-off).
• Pinch-off allows for controllable current flow in the JFET.

Conclusion

• Understanding JFET is crucial for electronic applications.
• Further discussions in next session.