The junction-gate field-effect transistor (JFET) is one of the simplest types of field-effect transistor. JFETs are three-terminal semiconductor devices that can be used as electronically controlled switches or resistors, or to build amplifiers. Unlike bipolar junction transistors, JFETs are exclusively voltage-controlled in that they do not need a biasing current.

1. B.Sc. II
Dr. Vaishali V. Deshmukh
Dept. of Physics
Shri Shivaji Science College,
Amravati
Solid State Devices-II

2. JFET
Lecture 3

3. What is FET? , features
Introduction
01
JFET, MOSFET
Types
02
JFET
03
Comparison of BJT and FET
04
Outline
Construction, Working, V-I characteristics and Parameters

4. JFET
The Junction Field Effect Transistor, or JFET, is a voltage controlled three terminal unipolar semiconductor
device available in N-channel and P-channel configurations
Bipolar Transistor
(BJT)
Field Effect
Transistor (FET)
Emitter – (E) >> Source – (S)
Base – (B) >> Gate – (G)
Collector – (C) >> Drain – (D)
Types of FET

5. FET and BJT
Typical Field Effect
Transistor

6. JFET and BJT

7. JFET as an Amplifier

10. Output characteristics of JFET

11. The characteristics curves in Fig, shows the four different
regions of operation for a JFET and these are given as:
1. Ohmic Region – When VGS = 0 the depletion layer of
the channel is very small and the JFET acts like a voltage
controlled resistor.
2. Cut-off Region – This is also known as the pinch-off
region were the Gate voltage, VGS is sufficient to cause the
JFET to act as an open circuit as the channel resistance is
at maximum.
3. Saturation or Active Region – The JFET becomes a
good conductor and is controlled by the Gate-Source
voltage, ( VGS ) while the Drain-Source voltage, ( VDS )
has little or no effect.
4. Breakdown Region – The voltage between the Drain
and the Source, ( VDS ) is high enough to causes the
JFET’s resistive channel to break down and pass
uncontrolled maximum current.
Fig: Drain V-I characteristics for n-channel JFET
1. VGS and VDS both=0
2. Self pinch off at no bias(VGS =0)
3. VGS with negative bias
4. Breakdown Region

12. Transfer charactristics for n-channel JFET
The transfer characteristic is drawn between gate voltage and drain
current by keeping drain to source voltage at pinch-off voltage.
When the gate is in zero potential the maximum drain current
flowing through the transistor is shorted gate drain current(IDSS).
Now as the negative potential of the gate increases the
corresponding drain current get decreased. After a certain negative
gate voltage, the drain current becomes zero. This negative gate
terminal voltage at which drain current becomes zero for the applied
drain to source voltage same as pinch-off voltage is called gate to
source cut off voltage VGS(off).

13. Features of JFET

14. Applications of JFET
JFET Applications
JFET is used as a switch.
JFET is used as a chopper.
Used as an amplifier.
Used as a buffer.
Used in the oscillatory circuits because of its low
frequency drift.
Used in digital circuits, such as computers, LCD and
memory circuits because of their small size.
Used in communication equipments, such as FM and TV
receivers because of their low modulation distortion.
Used as voltage controlled resistors in operational
amplifiers.
JFETs are used in cascade amplifiers and in RF
amplifiers.

15. Science is a
field which
grows
continuously
with ever
expanding
frontiers. “The combined results of several people working together
is often much more effective than could be that of an
individual scientist working alone.”

16. THANK YOU