This document describes the components and operation of an N-channel JFET transistor. It has three main parts: 1) The source, drain, and gate components, with the channel between the gate regions allowing majority carriers to flow from source to drain. 2) Increasing the gate-source voltage widens the depletion region, decreasing the channel width and thereby controlling the current from drain to source. 3) The drain characteristics show three regions: an ohmic region, a saturation region where current is independent of drain-source voltage, and a cut-off region where no current flows.

1. N- CHANNEL J-FET
Presented By
Shirisha Reddymalla..

2. N-CHANNEL J-FET
Here we have 3-components
1.SOURCE
2.DRAIN
3.GATE
SOURCE : where majority charge carries entires the
substrate called as source.

3. N-CHANNEL J-FET
• DRAIN : The terminal where the majority charge carries leave the path called as Drain.
GATE: On both sides of the n-type substrates heavily doped p+ region or acceptor ions
have been formed by alloying or diffusion .this impurity region is called as GATE.
CHANNEL: The region of the N-type material between 2-gate region the channel. The
channel is the path through which the majority carriers move from source to drain

4. FET OPERATION
 Vds is +ve in order to move electron from source to
drain
 At the drain the junction is reverse bised compared to
source
 The widing of depletion width is by
 1)conducting to the +ve voltage to the n-type material
 Connecting +ve voltage to the p-type (at the gate ) so the
gate is reverse bised w.r.t source as Vgs increases
negately .The width of the depletion layer increases the
channel gets decreases

5. CONDITIONS IN J-FET
Case1:VGS =0
1) Vgs increases then depletetion region at drain
increase and Id increases
2) At a particular point the two layers will touch each
other then that point is called as ‘‘pinch off point’’.
3) At a particular voltage the two depletion width touch
each other then that point is called as ‘‘pinch off voltage’’.
4) After pinch off point the VGS=0 or VGS=+ve then ID is
constant.

6. J-FET
CASE:2
1)VGS negatively increases then..
Depletion width increases so that channel
width decreases width.
For VDS constant as VGS negatively
increases the channel width decreases.

7. CHARACTERISTICS OR
DRAIN
CHARACTERISTICS
Here we have 3 regions
1) Ohmic region
2) saturation
3) Cut off region

8. OHMIC REGION
• VDS >0 and VDS < V GS –VP this is called as ohmic region
• There is no pinch of the channel here
• When VGS increases negatively then the channel conductance decreases therefore
resistance increases
• So the J-FET can be used as a voltage control resistor
• ID =f(VDS )
• As V DS varies therefore ID is also varies
• The resistor in the ohmic region is typically varies from 100 ohms to 10K ohms

9. SATURATION REGION
• VDS >VGS –vp
ID is independent of VDS
ID is dependent of VGS
ID=f(VGS )
ID =IDSS (1- VGS/VP) ²

10. CUT -OFF
• |VGS|> | VP| implies ID =0
• For the JFET to work as a amplifier it is to be operated in “saturation region”.
• Output current depends on input voltage. Hence it is called as Trans Conductance
Device.