Why should a JFET be operated with only reverse bias on the gate-source?

Reason for JFET is always reverse biased Due to “depletion region” surface reduction increases the resistance of the drain source and reduces the current flow and so JFET is always reverse biased. This bias leads to the formation of a “depletion layer” within the channel and the width of which increases with bias.

What are the condition for which JFET act as independent current source?

A JFET can be made to operate as a voltage controlled constant current source whenever its gate-source junction is reverse biased, and for an N-channel device we need a -VGS and for a P-channel device we need a +VGS.

Why is the input impedance to a JFET so high?

Since the Gate junction is reverse biased and because there is no minority carrier contribution to the flow through the device, the input impedance is extremely high. The control element for the JFET comes from depletion of charge carriers from the n-channel.

Why JFET is voltage controlled device?

JFET is a three-terminal device and since gate voltage controls the drain current, JFET is called a voltage-controlled device. JFET’s have only a depletion mode of operation. Thus drain current in JFET is controlled by changing the channel width.

What is transconductance and how does it depend on output voltage?

1. Transconductance. Transconductance is the property of certain electronic components. Conductance is the reciprocal of resistance; transconductance is the ratio of. the current change at the output port to the voltage change at the input port.

How is the transconductance of a JFET determined?

The transconductance cruve of a JFET transistor is the the graph of the drain current, ID verses the gate-source voltage, VGS. The ratio of change in drain current, ∆ID, to the change in gate-source voltage, ∆VGS, is the transconductance, gm.

What is saturation current in JFET?

The Saturation Region of a FET transistor is the region where the drain current, ID, flowing from the drain to the source of the FET transistor, is the highest for the gate-source voltage, VGS, that is supplied. The saturation current when VGS= -2V is approximately 6mA.

What is the condition of JFET when maximum current will flow?

With no external Gate voltage ( VG = 0 ), and a small voltage ( VDS ) applied between the Drain and the Source, maximum saturation current ( IDSS ) will flow through the channel from the Drain to the Source restricted only by the small depletion region around the junctions.

Why the channel of JFET is never completely closed at drain end?

However the channel never completely closes. The reason for this is that the electrostatic forces between the electrons cause them to spread out, giving a counter effect to the increase in thickness of the depletion layer.