The characteristics of a JFET

Question

I understand that when Vgs = 0, and there is a steady current Vds, there is a pinching shaped depletion region and so on. But what I have a confusion with is when Vgs > 0 or Vgs < 0.

The book states that when Vgs < 0, the Vds current will be less and the pinched depletion region will be achieved at lower Ids. My explanation is that since some of the charge from the source moves to the source between Vgs, the current/charge flow decreases, but since Vds remains same, the depletion pinched region stays the same. Is this correct?

In case of a positive connection to g between Vgs, i.e. Vgs > 0v I can't think of what happens.

Answer 1

When VGS < 0.6 or so, a depletion region is formed between the gate and the channel (which is the conductive region between the drain and source). As VGS becomes more negative, this depletion region widens further into the channel, 'squeezing' the conductive region -- thereby reducing the current that flows.

With positive VGS (up to ~ 0.6 V or so), the depletion region narrows, and the device would run more current.

With VGS even greater than this, the gate-channel junction is forward biased, and a large gate-source current flows. This is generally not a useful mode of operation. Depending on the structure of the device, drain current may change also.