Difference Between FET and BJT
Introduction
Field Effect Transistors (FETs) and Bipolar Junction Transistors (BJTs) are two common types of transistors used in electronic circuits. Although both operate as amplifiers, switches, and voltage regulators, they differ in their construction, operation, and performance characteristics.
FET vs. BJT: Construction
BJTs are constructed using a combination of p-type and n-type semiconductor materials. They consist of three layers – the emitter, the base, and the collector. A current flows from the emitter to the base, which then controls the flow of current between the collector and the emitter.
On the other hand, FETs are built using a single semiconductor material, either p-type or n-type. FETs have three terminals – the source, the gate, and the drain. A voltage applied to the gate controls the flow of current between the source and the drain, creating a channel that allows for the flow of electrons.
FET vs. BJT: Operation
BJTs operate by controlling the flow of current through a base-emitter junction. The amount of current flowing through the transistor is proportional to the current flowing into the base. BJTs are known for their high gain, low output impedance, and relatively fast switching speed.
FETs, on the other hand, operate by controlling the flow of current through a channel created by a voltage applied to the gate terminal. The current flowing through the channel is proportional to the voltage applied to the gate. FETs are known for their high input impedance, low output impedance, and low noise performance.
FET vs. BJT: Performance Characteristics
BJTs are suitable for high-power applications, such as power amplifiers, due to their high gain and fast switching speed. However, they may generate more heat than FETs, and can suffer from higher noise levels when used in low-power applications.
FETs are better suited for low-power applications when low noise performance is required. They operate at lower voltages than BJTs, and generate less heat, making them more efficient. FETs also have higher input impedance, which means they are less sensitive to loading effects from other components in the circuit.
Conclusion
In summary, BJTs and FETs are two common types of transistors that differ in their construction, operation, and performance characteristics. BJTs are suitable for high-power applications, while FETs are better suited for low-power applications when low noise performance is required. Understanding the differences between these two types of transistors is essential for selecting the appropriate device for a particular circuit design.
Table difference between fet and bjt
| Parameter | FET (Field Effect Transistor) | BJT (Bipolar Junction Transistor) |
|---|---|---|
| Operating principle | Uses electric field to control current | Uses current to control current |
| Polarity | Unipolar (negative or positive) | Bipolar (both negative and positive) |
| Application | Used as amplifiers, switches, and in digital circuits | Used as amplifiers, switches and in digital circuits |
| Input impedance | High | Low |
| Output impedance | Low | High |
| Size | Small | Large |
| Power requirements | Low power | High power |