What are the three regions of JFET?
JFET Characteristics
- Ohmic Region. The only region in which transconductance curve shows linear response and drain current is opposed by the JFET transistor resistance is termed as Ohmic region.
- Saturation Region.
- Cutoff Region.
- Breakdown Region.
What is cutoff region in P channel JFET?
Ohmic Region – When VGS = 0 the depletion layer of the channel is very small and the JFET acts like a voltage controlled resistor. Cut-off Region – This is also known as the pinch-off region were the Gate voltage, VGS is sufficient to cause the JFET to act as an open circuit as the channel resistance is at maximum.
What is the main principle of JFET?
For this reason it is known as Field Effect Transistor. Hence, the JFET operates on the principle that the width and resistance of conduction channel can be varied by changing the reverse voltage VGS.
Why is the depletion region narrower in JFET transistor?
In this diagram of JFET transistor the depletion region is narrower at one end and wider at other end. Why is that so? Is it due to the voltages applied at gate and drain? Yes it is – the depletion will be wider at the drain because it is connected to the positive of the battery whereas the source is at a voltage closer to that on the gate.
How is the output current of a JFET controlled?
A JFET is a unipolar device, which differs in operation from a bipolar junction transistor. The output current of a JFET is controlled by the voltage on the gate. The gate voltage creates an electrical field, or depletion region, within the device. See Figure 2.
When does the depletion region of a JFET grow?
As the gate gets more negative the depletion region will grow and eventually the device will be deemed to be “cut-off” and exhibit only low leakage currents from drain to source. This is an N channel JFET. P channel JFETs operate the same but with both batteries reversed.
Why are JFETs referred to as depletion mode devices?
JFETs are sometimes referred to as depletion-mode devices as they rely on the principle of a depletion region which is devoid of majority charge carriers; and the depletion region has to be closed to enable current to flow.