BJT Transistors Structure and Operation

BJT Transistors

Structure

• Consist of three layers: emitter, base, and collector
• Two types: NPN (negative-positive-negative) and PNP (positive-negative-positive)

Operation

• Current flows from emitter to collector, controlled by base-emitter voltage
• Base-emitter junction acts as an amplifier, allowing small input signal to control large output current

Modes of Operation

• Active mode: transistor acts as an amplifier, allowing current to flow from emitter to collector
• Cut-off mode: transistor is fully turned off, no current flows between emitter and collector
• Saturation mode: transistor is fully turned on, maximum current flows between emitter and collector

Applications

• Amplifiers
• Switches
• Logic gates

FET Transistors

Structure

• Consist of three layers: source, gate, and drain
• Two types: N-channel and P-channel

Operation

• Current flows from source to drain, controlled by gate-source voltage
• Gate-source junction acts as a capacitor, allowing small input signal to control large output current

Modes of Operation

• Ohmic mode: transistor acts as a resistor, allowing current to flow from source to drain
• Saturation mode: transistor is fully turned on, maximum current flows between source and drain
• Cut-off mode: transistor is fully turned off, no current flows between source and drain

Applications

• Amplifiers
• Switches
• Logic gates
• Integrated circuits

Comparison of BJT and FET Transistors

• BJT: high current gain, high input impedance, but requires more power to operate
• FET: low current gain, high input impedance, but requires less power to operate
• FET is more suitable for high-frequency applications, while BJT is more suitable for low-frequency applications

BJT Transistors

Structure

• Composed of three layers: emitter, base, and collector
• NPN (negative-positive-negative) and PNP (positive-negative-positive) are the two main types

Operation

• Current flow from emitter to collector is controlled by the base-emitter voltage
• Base-emitter junction acts as an amplifier, enabling small input signals to control large output currents

Modes of Operation

• Active mode: transistor acts as an amplifier, allowing current to flow from emitter to collector
• Cut-off mode: transistor is fully turned off, preventing current flow between emitter and collector
• Saturation mode: transistor is fully turned on, resulting in maximum current flow between emitter and collector

Applications

• Amplifiers: BJT transistors are used to amplify weak electrical signals
• Switches: BJT transistors are used to switch electronic circuits on and off
• Logic gates: BJT transistors are used to create logical operations in digital circuits

FET Transistors

Structure

• Composed of three layers: source, gate, and drain
• N-channel and P-channel are the two main types

Operation

• Current flow from source to drain is controlled by the gate-source voltage
• Gate-source junction acts as a capacitor, enabling small input signals to control large output currents

Modes of Operation

• Ohmic mode: transistor acts as a resistor, allowing current to flow from source to drain
• Saturation mode: transistor is fully turned on, resulting in maximum current flow between source and drain
• Cut-off mode: transistor is fully turned off, preventing current flow between source and drain

Applications

• Amplifiers: FET transistors are used to amplify weak electrical signals
• Switches: FET transistors are used to switch electronic circuits on and off
• Logic gates: FET transistors are used to create logical operations in digital circuits
• Integrated circuits: FET transistors are used in the construction of integrated circuits

Comparison of BJT and FET Transistors

• BJT transistors have high current gain, high input impedance, but require more power to operate
• FET transistors have low current gain, high input impedance, but require less power to operate
• FET transistors are more suitable for high-frequency applications, while BJT transistors are more suitable for low-frequency applications