WHY JFET IS CALLED UNIPOLAR TRANSISTOR

WHY JFET IS CALLED UNIPOLAR TRANSISTOR

WHY JFET IS CALLED UNIPOLAR TRANSISTOR

Fet is a Field Effect transistor. A transistor is a piece of semiconductor that has three terminals, and depending on the voltage applied between two of them, the current through the third can be controlled.

1. BIPOLAR JUNCTION TRANSISTOR (BJT)

BJT is the conventional transistor with two PN junction diodes connected back to back. For example, the NPN transistor has an N-type emitter, a P-type base, and an N-type collector. At first, the base and emitter are considered forward biased, and the collector is reverse biased. As more voltage is applied, more majority carries (electron) from the emitter are injected into the base region across the emitter junction. This increases the base current, which is amplified and enters the collector terminal.

2. FIELD EFFECT TRANSISTOR (FET)

FET operates on the principle of the electric field effect. It has a single PN junction between source and drain terminals, and a third terminal called gate. There are two main types of FETs – JFETs (Junction Field Effect Transistor) and MOSFET (Metal Oxide Semiconductor Field Effect Transistor). Both of these function on the principle of majority carrier flow.

2.1. JFET (JUNCTION FIELD EFFECT TRANSISTOR)

JFET is also known as unipolar transistor because it uses only one type of charge carrier, either electron or hole. This property makes JFETs different from BJT (Bipolar Junction Transistor), which uses both majority and minority carriers.

2.2. WORKING PRINCIPLE

JFET is a voltage-controlled device. The voltage applied between the gate and the source terminals controls the flow of current between the drain and source terminals. When the voltage is applied, the potential barrier formed at the PN junction is changed and this alters the amount of current flowing through the device.

2.3. TYPES OF JFET

There are two types of JFETs:

i) N-channel JFET: It has an N-type channel and a P-type gate.
ii) P-channel JFET: It has a P-type channel and an N-type gate.

3. WHY JFET IS CALLED UNIPOLAR TRANSISTOR

JFET is called unipolar transistor because it uses only one type of charge carrier, either electron (in N-channel JFET) or hole (in P-channel JFET). This is in contrast to BJT, which uses both majority and minority carriers.

3.1. ADVANTAGES OF JFET

a) High input impedance
b) Low noise
c) Wide bandwidth
d) Less prone to thermal runaway

3.2. DISADVANTAGES OF JFET

a) Lower current handling capacity
b) Lower transconductance
c) Sensitive to temperature changes

4. APPLICATIONS OF JFET

JFETs are used in various electronic applications, including:

a) Amplifiers
b) Switches
c) Buffers
d) Mixers
e) Voltage-controlled attenuators

Conclusion

JFET is a 3 terminal semiconductor device that works by the modulation of majority carriers.
It is called a unipolar transistor because it uses only one type of charge carrier.
JFETs are commonly used in a variety of electronic circuits, such as amplifiers, switches, mixers, and voltage-controlled attenuators.

FREQUENTLY ASKED QUESTIONS (FAQs)

1. What is the difference between a BJT and a JFET?
A: BJT uses both majority and minority carriers, while JFET uses only one type of charge carrier.

2. Why is JFET called a unipolar transistor?
A: Because it uses only one type of charge carrier.

3. What are the advantages of a JFET?
A: High input impedance, low noise, wide bandwidth, and less prone to thermal runaway.

4. What are the disadvantages of a JFET?
A: Lower current handling capacity, lower transconductance, and sensitive to temperature changes.

5. What are the applications of a JFET?
A: Amplifiers, switches, buffers, mixers, and voltage-controlled attenuators.

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