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