Electronics - Field Effect Transistors (FET) - Discussion

The pinch-off voltage for an N-channel JFET is 4V. When VGS=1V, lVDS(min)l at which pinch-off occurs is equal to

*N-type JFET is operated with VGS<=0; (i.e., reverse gate to source).
* VGS controls ID.

When VGS=0, IDSS=maximum current.
Assuming, initially, VGS=0;

Option A:

Now if we decrease VGS (more negative), then ID decreases; (Option A is correct only if we are given assumption " Assuming, initially, VGS=0;". Note, A and B are giving same meaning if this assumption is not considered.)

Option B:

Increasing VGS(greater than 0), will not increase current as N-channel JFET requires negative VGS for its operation (and thus for to be in constant current region for any VGS.)
Option C and D cannot be correct as VGS controls ID. In constant-current region, current is constant wrt VDS and not VGS.

Yes as VGS decreases ID decreases but also when VGS increases ID remains constant so I think option D is also correct.

The correct option is D. Because constant current region means saturation region, so as Vgs increases Id remains constant.

This is simple explanation that depends on the depletion region, as Vgs increases, it tend to increase the depletion region. As the depletion region decreases it tends to allow less electrons flow through the channel, as the number of electrons flowing through the channel decreases then current also decreases.

When Vgs increases like 0v, 1v, 2v... Id also increases. According to the graph that we plot Id vs Vds as a function of Vgs.

As Vgs (reverse bias voltage gate to source) increases Id decreases because increase in Vgs causes to increase the depletion region and reduce the effective width of the channel so Id will decreases. And if we made Vgs positive Id will remain constant for n channel JFET.

As the drain to source voltage is increased this depletion region also widens narrowing down the channel at point both the regions touch pinching off the channel, the drain current increases linearly at first but after pinch off voltage it becomes constant.

Both A and D are correct as for me. Because in constant region Ids remains constant till breakdown region occurs.

Answer is 1.

As channel depends on Vgs and Ids depends on channel. So we can say Ids is proportional to Vgs.