What is Field Effect Transistor (FET)? || Differences between BJT and FET || Types of FET

Summary

This video from the ALL ABOUT ELECTRONICS YouTube channel offers a concise introduction to Field Effect Transistors (FETs), highlighting their role in controlling current flow through an electric field. It differentiates FETs from Bipolar Junction Transistors (BJTs), emphasizing FETs' high input impedance, smaller size, and lower power consumption, making them ideal for integrated circuits and high-power applications. The video also touches on the two main types of FETs: JFETs, which use a reverse-biased PN junction for gate control, and IG-FETs, like the widely used MOSFETs, which feature an insulated gate. The script promises upcoming videos that will delve into the operation, symbols, and characteristics of these FETs.

Takeaways

• 📗 The Field Effect Transistor (FET) is a three-terminal device that controls current flow using an electric field.
• ⚡ FETs are widely used in integrated circuits, including computers, due to their efficient current control.
• 🔗 The three terminals of the FET are gate, drain, and source, with current flowing between drain and source, controlled by the voltage between gate and source.
• 💡 FETs are voltage-controlled devices, in contrast to Bipolar Junction Transistors (BJTs), which are current-controlled.
• 🔍 FETs are unipolar devices (relying on one type of charge carrier), while BJTs are bipolar devices (relying on both electrons and holes).
• ⚙️ FETs have high input impedance, making them ideal for use as buffer amplifiers, and are smaller and more power-efficient than BJTs.
• 📊 FETs come in two main types: Junction Field Effect Transistors (JFET) and Insulated Gate Field Effect Transistors (IG-FET), with MOSFET being the most common IG-FET.
• 🔋 The two types of MOSFETs are depletion mode (decreases charge carriers) and enhancement mode (increases charge carriers).
• 🔗 MOSFETs can be further classified into n-channel and p-channel types, based on the material used in the channel.
• 🧪 FETs are used in various applications, such as amplifiers, oscillators, analog switches, and in computing devices for low power consumption.

Q & A

What is a Field Effect Transistor (FET)?

A Field Effect Transistor (FET) is a three-terminal device that uses an electric field to control the flow of current through the device. It is widely used in many applications, including integrated circuits and computers.

What are the three terminals of an FET?

The three terminals of an FET are known as gate, drain, and source.

How does the current flow in an FET?

In an FET, the current flows between the drain and the source terminals, and this flow can be controlled by applying a voltage between the gate and the source terminals.

What is the difference between a FET and a Bipolar Junction Transistor (BJT) in terms of control mechanism?

FETs are voltage-controlled devices, where the input voltage between the gate and source controls the output current. In contrast, BJTs are current-controlled devices, where the input base current controls the output collector current.

Why are FETs considered unipolar devices?

FETs are considered unipolar devices because their operation relies on either holes or electrons, but not both, unlike BJTs which rely on both types of charges.

What is the significance of high input impedance in FETs?

The high input impedance of FETs makes them suitable for use as buffer amplifiers in many applications, as they can provide high resistance to the input signal without significantly altering it.

How do FETs compare to BJTs in terms of size and power consumption?

FETs are generally smaller in size compared to BJTs and have lower power consumption, which is why they are commonly used in integrated circuits and preferred in high power and computing applications where minimal power consumption is required.

What are the two main types of FETs discussed in the script?

The two main types of FETs discussed are the Junction Field Effect Transistor (JFET) and the Insulated Gate Field Effect Transistor (IG-FET), with MOSFET being the most common type of IG-FET.

How does a JFET control the flow of current through its channel?

In a JFET, the gate terminal is provided using a PN junction. When this PN junction is reverse-biased, the depletion region isolates the gate terminal from the channel, controlling the flow of current.

What is the difference between depletion and enhancement type MOSFETs?

In a depletion type MOSFET, the applied voltage at the gate terminal depletes the charge carriers in the channel, while in an enhancement type MOSFET, the applied voltage enhances the number of charge carriers, forming a channel between two n-regions.

What are the two classifications of MOSFETs based on the channel material?

MOSFETs can be classified as either n-channel or p-channel, depending on whether the channel is made of n-type or p-type semiconductor material.