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A transistor is a _____ operated device.
Current
Voltage
Both
None
Current
A Bipolar Junction Transistor (BJT) is defined as a current-operated device because the output collector current (ICтАЛ) is controlled by the input base current (IBтАЛ). The relationship between these currents is governed by the common-emitter current gain, denoted as ╬▓ or hfeтАЛ.
A Bipolar Junction Transistor (BJT) is defined as a current-operated device because the output collector current (ICтАЛ) is controlled by the input base current (IBтАЛ). The relationship between these currents is governed by the common-emitter current gain, denoted as ╬▓ or hfeтАЛ.
ICтАЛ=╬▓IBтАЛ тАФ Collector current as a function of base current and gain
IEтАЛ=IBтАЛ+ICтАЛ тАФ Conservation of current in a BJT
In a BJT, the movement of charge carriers across the base-emitter junction establishes the base current. This small input current modulates the wider depletion region at the collector-base junction, allowing a significantly larger flow of electrons (or holes) from emitter to collector. The fundamental operation is summarized by the gain equation ICтАЛ=╬▓IBтАЛ.
The BJT operates based on the minority carrier injection principle.
BJT is current-controlled, whereas Field Effect Transistors (FETs) are voltage-controlled devices.
The base region is intentionally kept very thin and lightly doped to facilitate carrier transition.
High current gain
Fast switching speeds in small-signal applications
Higher power consumption compared to MOSFETs
Subject to thermal runaway if not biased correctly
Signal amplification in audio circuits
Digital switching in logic gates
| Feature | BJT | FET/MOSFET |
|---|---|---|
Control Parameter | Current | Voltage |
The term 'current-operated' refers to the fact that the output collector current is a direct function of the input base current.
Option B is incorrect because transistors categorized as voltage-operated devices are typically FETs or MOSFETs, where the gate-source voltage (VGSтАЛ) controls the drain-source current (IDтАЛ).
A is correct тАФ The Bipolar Junction Transistor is classified as a current-operated device because the output current is fundamentally dependent on the input base current.
Always remember: BJT = Current controlled (IBтАЛ controls ICтАЛ), FET = Voltage controlled (VGSтАЛ controls IDтАЛ).