JFET Construction, Working Principle And V-I Characterstics

JFET (Junction Field Effect Transistor)
It is a voltage controlled semiconductor device.
In this, the current is carried by only one type of carriers.
So, it is a Unipolar device (one polarity of charge carrier)
No minority carrier storage
JFET consists of a doped Si

1. A Presentation On
JFET
It’s Construction,
Working Principle
And V-I Characterstics

Prepared By:
Biplap Bhattarai

2. JFET (Junction Field Effect Transistor)
It is a voltage controlled semiconductor device.
In this, the current is carried by only one type of carriers.
So, it is a Unipolar device (one polarity of charge carrier)
No minority carrier storage
JFET consists of a doped Si

3. P P
+
-
+
-
+
-
N
N
Construction of a JFET
Gate
Drain
Source

4. •JFET output characteristics For Vgs
Pinch off region
Breakdown

5. •Operation
–the reverse-biased gate junction produced a
depletion layer in the region of the channel
–the gate volt controls the thickness of the depletion
layer and hence the thickness of the channel
–consider an n-channel device
•the gate will always be negative with respect to the
source to keep the junction between the gate and the
channel reverse-biased
•making the gate more negative increases the thickness of
the depletion layer, reducing the width of the channel –
increasing the resistance of the channel.

6. The JFET
6
•Characteristics:
no saturation saturation

7. •JFET circuit symbols

8. •Notation
–FETs are 3 terminal devices
•drain (d)
•source (s)
•gate(g)
–the gate is the control
input
–diagram illustrates the
notation used for labelling
voltages and currents

9. Summary of JFET Characteristics
•FETS have three terminals: drain, source and gate
•The gate is the control input
•Two polarities of device: n-channel and p-channel
•In each case the drain current is controlled by the
voltage applied to the gate with respect to the source
•Behaviour is characterised by the transconductance
•The operating point differs between devices