BJT is a _____a)Voltage controlled deviceb)Current controlled devicec)...
BJT stands for Bipolar junction transistor
- B = Bipolar (because conduction is due to two opposite type of carriers Holes and electrons)
- J = Junction refers to the two PN junctions between emitter and base, and collector and base.
- BJT's are current-driven devices i.e. It is a current-controlled device.
- The current through the two terminals is controlled by a current at the third terminal (base).
- It is a bipolar device (current conduction by both types of carriers, i.e. majority and minority electrons and holes)
- It has a low input impedance.
Symbol
BJT is a _____a)Voltage controlled deviceb)Current controlled devicec)...
Brief Explanation:
BJT stands for Bipolar Junction Transistor. It is a three-layer semiconductor device that can amplify or switch electronic signals and electrical power. It has three regions, namely the emitter, base, and collector. The BJT can be classified into two types: NPN (Negative-Positive-Negative) and PNP (Positive-Negative-Positive) transistors. The base current controls the collector current in a BJT, making it a current-controlled device.
Detailed Explanation:
Voltage Controlled Device:
- A voltage controlled device is one in which the output characteristics are controlled by the input voltage applied to it.
- The voltage-controlled device has a high input impedance and low output impedance.
- Examples of voltage-controlled devices include operational amplifiers, field-effect transistors (FETs), and MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors).
Current Controlled Device:
- A current controlled device is one in which the output characteristics are controlled by the input current applied to it.
- The current-controlled device has a high input impedance and low output impedance.
- Examples of current-controlled devices include bipolar junction transistors (BJTs) and vacuum tubes.
BJT as a Current Controlled Device:
- A BJT is a current controlled device because the collector current (output) is controlled by the base current (input).
- In an NPN transistor, when a small base current is applied, it controls a much larger collector current.
- The base current determines the amount of current flowing through the collector-emitter path.
- The base-emitter junction is forward biased, and the base-collector junction is reverse biased in normal operation.
- The base-emitter current (input current) controls the collector current (output current) through the transistor.
- The ratio of the collector current to the base current is called the current gain or beta (β) of the transistor, typically ranging from 20 to 1000.
- This current amplification property makes the BJT suitable for amplification and switching applications.
Conclusion:
In conclusion, the correct answer is option 'B': BJT is a current controlled device. The base current controls the collector current in a BJT, making it a current-controlled device rather than a voltage-controlled device.
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