Difference Between BJT and FET
Introduction: If you’ve ever delved into the world of electronics, you must have come across terms like BJT and FET. Both are essential electronic devices used extensively in various applications. In this article, we will explore the differences between BJT (Bipolar Junction Transistor) and FET (Field Effect Transistor), their respective uses, and provide examples to help you understand them better.
What is BJT?
BJT, short for Bipolar Junction Transistor, is a three-layer semiconductor device consisting of two junctions, namely the emitter-base junction and the base-collector junction. It is widely used as an amplifier or a switch in electronic circuits.
Examples of BJT:
- NPN Transistor: 2N3904
- PNP Transistor: 2N3906
Uses of BJT:
BJTs find applications in a wide range of electronic devices, including but not limited to:
- Amplifiers
- Oscillators
- Power control circuits
- Radio and television receivers
What is FET?
FET, or Field Effect Transistor, is a three-terminal semiconductor device that relies on the electric field between the source and the drain to control the conductivity of a channel. It is commonly used as an amplifier, switch, or even an oscillator.
Examples of FET:
- MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor)
- JFET (Junction Field Effect Transistor)
Uses of FET:
FETs are extensively used in numerous electronic applications, including:
- Audio amplifiers
- Signal mixers and detectors
- Electrometers and voltmeters
- High-frequency applications
Differences Between BJT and FET:
| Difference Area | BJT | FET |
|---|---|---|
| Construction | Consists of two PN junctions | Constructed with a doped semiconductor material |
| Polarity | Exist in both PNP and NPN types | Exist in N-channel and P-channel types |
| Control | Controlled by current | Controlled by voltage |
| Input Impedance | Low input impedance | High input impedance |
| Output Impedance | High output impedance | Low output impedance |
| Gain | Low voltage gain and high current gain | High voltage gain and low current gain |
| Operating Temperature | More sensitive to temperature changes | Less sensitive to temperature changes |
| Noise | Susceptible to noise | Analog FETs have lower noise levels |
| Frequency Response | Less frequency dependent | Dependent on the gate capacitance |
| Manufacturing Cost | Relatively lower manufacturing cost | Higher manufacturing cost due to complex processing |
Conclusion:
In summary, BJT and FET are both crucial semiconductor devices used in various electronic applications. While BJT utilizes current control and has low input impedance, FET employs voltage control and features high input impedance. BJT has a high output impedance and is more sensitive to temperature changes compared to FET. Additionally, BJT is more susceptible to noise and operates with less frequency dependence. The manufacturing costs also differ, with BJT having a relatively lower cost compared to FET.
People Also Ask:
Here are some common questions readers may have about BJT and FET:
Q1. What is the main difference between BJT and FET?
A1. The main difference lies in the way they are controlled – BJT is controlled by current, whereas FET is controlled by voltage.
Q2. Which transistor type has higher input impedance?
A2. FET exhibits higher input impedance compared to BJT.
Q3. Which transistor type has higher voltage gain?
A3. FET generally has higher voltage gain compared to BJT.
Q4. Are FETs more expensive to manufacture than BJTs?
A4. Yes, FETs typically have a higher manufacturing cost due to their complex processing.
Q5. Which transistor type is more sensitive to temperature changes?
A5. BJT is more sensitive to temperature changes compared to FET.
