1 Answer
The main difference between **BJT (Bipolar Junction Transistor)** and **FET (Field-Effect Transistor)** lies in how they are controlled and how current flows through them:
1. **Current Control Mechanism:**
- **BJT:** In a BJT, current flows through the transistor based on the **voltage between the base and emitter**, but the actual current flow is controlled by the **current at the base**. This means BJTs are **current-controlled** devices.
- **FET:** In a FET, current flow is controlled by the **voltage applied to the gate**. The gate essentially creates an electric field that controls the flow of current between the source and drain. FETs are therefore **voltage-controlled** devices.
2. **Types of Charge Carriers:**
- **BJT:** In BJTs, both **electrons** and **holes** are involved in conduction, meaning they are **bipolar** devices. This is why they’re called "Bipolar Junction Transistors."
- **FET:** FETs rely on only **one type of charge carrier** (either electrons in an N-channel FET or holes in a P-channel FET), making them **unipolar** devices.
3. **Power Efficiency:**
- **BJT:** BJTs tend to consume more power when active because they require a continuous current at the base.
- **FET:** FETs are generally more power-efficient because they consume very little current at the gate (essentially just enough to create the electric field).
4. **Input Impedance:**
- **BJT:** BJTs have a **lower input impedance** because of the base current requirement.
- **FET:** FETs have a **higher input impedance** since the gate current is almost negligible.
5. **Applications:**
- **BJT:** BJTs are often used in **amplification** and **switching circuits**, particularly when high current gain is required.
- **FET:** FETs are typically used in **digital circuits**, **low-power applications**, and **high-impedance circuits** due to their voltage-controlled nature and high input impedance.
To sum up: BJTs are **current-controlled** devices, while FETs are **voltage-controlled** devices, with FETs being more power-efficient and having higher input impedance.
1. **Current Control Mechanism:**
- **BJT:** In a BJT, current flows through the transistor based on the **voltage between the base and emitter**, but the actual current flow is controlled by the **current at the base**. This means BJTs are **current-controlled** devices.
- **FET:** In a FET, current flow is controlled by the **voltage applied to the gate**. The gate essentially creates an electric field that controls the flow of current between the source and drain. FETs are therefore **voltage-controlled** devices.
2. **Types of Charge Carriers:**
- **BJT:** In BJTs, both **electrons** and **holes** are involved in conduction, meaning they are **bipolar** devices. This is why they’re called "Bipolar Junction Transistors."
- **FET:** FETs rely on only **one type of charge carrier** (either electrons in an N-channel FET or holes in a P-channel FET), making them **unipolar** devices.
3. **Power Efficiency:**
- **BJT:** BJTs tend to consume more power when active because they require a continuous current at the base.
- **FET:** FETs are generally more power-efficient because they consume very little current at the gate (essentially just enough to create the electric field).
4. **Input Impedance:**
- **BJT:** BJTs have a **lower input impedance** because of the base current requirement.
- **FET:** FETs have a **higher input impedance** since the gate current is almost negligible.
5. **Applications:**
- **BJT:** BJTs are often used in **amplification** and **switching circuits**, particularly when high current gain is required.
- **FET:** FETs are typically used in **digital circuits**, **low-power applications**, and **high-impedance circuits** due to their voltage-controlled nature and high input impedance.
To sum up: BJTs are **current-controlled** devices, while FETs are **voltage-controlled** devices, with FETs being more power-efficient and having higher input impedance.