What is FET with BJT. Differentiate with the principle of working.

Q.) What is FET with BJT. Differentiate with the principle of working.

 Subject: electronic devices and circuits

Field-Effect Transistor (FET) vs Bipolar Junction Transistor (BJT):

FET (Field-Effect Transistor):

  • Principle of Working:
    • FETs are unipolar devices, meaning they conduct current using only one type of charge carrier (electrons or holes).
    • In a FET, the current through the device is controlled by an electric field generated by a voltage applied to a gate terminal.
    • The gate voltage modulates the width of a channel through which the current flows, effectively controlling the current.

Types of FETs:

  1. Junction FET (JFET):
    • Uses a reverse-biased PN junction to control the channel width.
  2. Metal-Oxide-Semiconductor FET (MOSFET):
    • Uses an insulated gate (usually silicon dioxide) between the gate and the channel.
    • Most common type of FET, widely used in ICs.

BJT (Bipolar Junction Transistor):

  • Principle of Working:
    • BJTs are bipolar devices, meaning they conduct current using both electrons and holes.
    • In a BJT, the current is controlled by injecting minority carriers (electrons in a PNP transistor and holes in an NPN transistor) into a thin region called the base.
    • The injected minority carriers are amplified by the base-emitter junction and collected by the base-collector junction, resulting in a larger collector current.

Types of BJTs:

  1. NPN Transistor:
    • Has an N-type emitter, a P-type base, and an N-type collector.
  2. PNP Transistor:
    • Has a P-type emitter, an N-type base, and a P-type collector.

Comparison:

Feature FET BJT
Charge Carriers Unipolar (electrons or holes) Bipolar (electrons and holes)
Current Control Gate voltage modulates channel width Base current controls collector current
Power Handling Capability Lower Higher
Switching Speed Faster Slower
Input Impedance High Low
Applications Amplifiers, switches, memory cells Amplifiers, switches, power transistors

In summary, FETs are unipolar devices controlled by an electric field, offering high input impedance and faster switching speeds. BJTs are bipolar devices controlled by minority carrier injection, providing higher power handling capability but slower switching speeds. Both FETs and BJTs have various applications in electronic circuits, including amplifiers, switches, and memory cells.