JFET is a Junction gate field-effect transistor. The normal transistor is a current-controlled device that needs current for biasing, whereas JFET is a voltage-controlled device. JFET has three terminals Gate, Drain, and Source.
We can use JFET as voltage-controlled resistors or as a switch, or even make an amplifier using the JFET. It is also an energy-efficient version to replace the BJTs. JFET provides low power consumption and fairly low power dissipations, thus improving the overall efficiency of the circuit
Types of JFET
- N Channel JFET
- P Channel JFET
Construction of JFET
JFET is constructed using the long channel of semiconductor material. Depending on the construction process, if the JFET contains a great number of positive charge carriers (refers as holes) is a P-type JFET, and if it has a large number of negative charge carriers (refers as electrons) is called N-type JFET.
In the long channel of semiconductor material, Ohmic contacts at each end are created to form the Source and Drain connections. A P-N junction is formed on one or both sides of the channel.
Working of JFET
Suppose a garden hose is providing a water flow through it. If we squeeze the hose the water flow will be less and at a certain point if we squeeze it completely there will be zero water flow. JFET works exactly in that way. If we interchange the hose with a JFET and the water flow with a current and then construct the current-carrying channel, we could control the current flow.
When there is no voltage across the gate and source, the channel becomes a smooth path that is wide open for electrons to flow. But the reverse thing happens when a voltage is applied between gate and source in reverse polarity, which makes the P-N junction reversed biased and makes the channel narrower by increasing the depletion layer and could put the JFET in a cut-off or pinch-off region.
If we want to switch off a JFET we need to provide a negative gate to source voltage denoted as VGS for an N-type JFET. For a P-type JFET, we need to provide positive VGS.
Biasing of JFET
- Fixed DC Biasing Technique
- Self-Biasing Technique
- Potential Divider Biasing
Application Of JFET
- Amplifiers Circuits
- Analog Switches
- AGC Systems
- Voltage Regulators