Answer to Question #85269 in Electric Circuits for Anand

Question

Describe the construction of Junction Field Effect Transistor and explain why it is
called a voltage controlled device.

Answer 1

The JFETs have no PN-junctions like bipolar transistors, they have two P-type (N-type) layers connected to the gate and separated by N-type (P-type) channel between them. The channel at its ends has two terminals called source and drain.

The JFET is a voltage controlled device because the PN junction is reverse biased during normal operation (gate to source), and by changing the gate-source voltage we can control its resistance by controlling the drain to source current which depends on width of the channel.