Transistors Overview and BJTs Analysis

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Questions and Answers

What happens to the base-emitter junction when it is properly biased?

It has no effect on current flow.

It becomes reverse biased.

It breaks down and stops working.

It becomes forward biased. (correct)

What type of biasing is present at the collector-base junction?

Reverse biased (correct)

Unstable bias

Forward biased

No bias present

Which statement accurately describes the flow of electrons in a properly biased NPN transistor?

Electrons do not flow at all.

Electrons flow from base to emitter.

Electrons flow from emitter to base. (correct)

Electrons only flow in reverse direction.

What does KCL state about the currents in an NPN transistor?

I_E = I_C + I_B (A) Signup and view all the answers

What does the reverse current in the collector-base junction typically consist of?

Minority carriers (D) Signup and view all the answers

What is the result of the correct biasing of an NPN transistor?

Current leaves the emitter terminal. (B) Signup and view all the answers

Why is it important for the base-emitter junction to be forward biased in a transistor?

To allow current to flow from emitter to base. (B) Signup and view all the answers

How does the biasing affect electron movement in a transistor?

Correct biasing facilitates the movement of electrons. (D) Signup and view all the answers

What type of MOSFET circuit is most commonly used for class 'A' amplifier applications?

Enhancement mode n-channel common source amplifier (A) Signup and view all the answers

What is the primary effect of high input impedance in MOSFETs?

Increased risk of damage from static electricity (D) Signup and view all the answers

In a common source MOSFET amplifier, what happens to the output voltage (Vout) when the gate voltage (VG) is high?

The output voltage decreases (D) Signup and view all the answers

Which component is primarily responsible for controlling the input impedance of a MOSFET?

Gate biasing resistive network (C) Signup and view all the answers

What happens to the MOSFET when the gate voltage (VG) is low?

The transistor is switched 'OFF' (B) Signup and view all the answers

How does a depletion mode MOSFET amplifier compare to a JFET amplifier?

They exhibit similar operational characteristics (B) Signup and view all the answers

What is the consequence of not properly protecting MOSFETs from static electricity?

Complete failure of the MOSFET (D) Signup and view all the answers

What leads to an inverted output signal in the enhancement mode common source amplifier?

The relationship between gate voltage and drain current (B) Signup and view all the answers

What is the relationship between collector current and base current in a BJT?

IC is equal to β multiplied by IB (C) Signup and view all the answers

What is a typical voltage for the base-emitter junction in a forward-biased BJT?

0.7V (C) Signup and view all the answers

In a BJT, which parameter is indicated by the symbol hFE?

Current gain (D) Signup and view all the answers

What usually characterizes the base current in a BJT?

It is typically in the μA range. (D) Signup and view all the answers

Which equation correctly describes the emitter current in terms of base current and beta?

IE = (1 + β)IB (C) Signup and view all the answers

In a reverse-biased BJT, how are majority carriers treated?

As minority carriers (D) Signup and view all the answers

What does a higher value of beta (β) in a BJT indicate?

Greater collector current for a given base current (B) Signup and view all the answers

What is primarily determined by the resistances in a BJT circuit?

Overall circuit gain (C) Signup and view all the answers

Study Notes

Transistors

Transistors are electronic components that can amplify or switch electronic signals and electrical power.
They are fundamental building blocks in various electronic devices.
Types of transistors: Bipolar Junction Transistors (BJTs), Junction Field Effect Transistors (JFETs), and Metal-Oxide Semiconductor Field Effect Transistors (MOSFETs).

Bipolar Junction Transistors (BJTs)

A BJT is a current-controlled device.
A three-layer device: Either PNP or NPN type transistor.
The "sandwiched" material has a smaller width (150:1 ratio) and is less doped (10:1 ratio) compared to the outer layers to decrease conductivity.
Transistor must be biased correctly for amplification.
In an NPN or PNP transistor, the BE junction is forward biased, and the BC junction is reverse biased.
Key factor: Base current magnitude is in µA range due to the sandwiched material's low conductivity.

JFETs (Junction Field Effect Transistors)

JFETs are voltage-controlled devices.
Two types: N-channel and P-channel.
Output current is dependent on the applied voltage.
Key factor: Increasing the absolute value of the gate-source voltage results in a reduced drain current.

MOSFETs (Metal-Oxide Semiconductor Field Effect Transistors)

MOSFETs are voltage-controlled devices.
Consists of a gate (control terminal) to control the output current.
Two types: N-channel and P-channel, enhancement-type or depletion-type.
High input impedance.
MOSFETs can be easily damaged by static electricity.

Transistor Configurations

Common-Base, Common-Emitter, Common-Collector
Input and output characteristics of CB and CE configurations are tackled to determine important quantities a and β.
Common-Base: Output changes as a result of input changes
Common-Emitter: Emitter terminal is the common/reference terminal to the input (base) terminal and the output (collector) terminal.
Common-Collector: Output current changes in proportion to the input current.

Transistor Operation

Transistor must be correctly biased for correct amplification.
Either an NPN or PNP transistor, the BE junction is forward biased, and the BC junction is reverse biased.
The net effect is a current leaving the emitter terminal of the transistor.
By KCL: IE = IC + IB.
Note that the transistor power is given by Pc = Vcelc

Important Parameters

Current (Base, Collector, Emitter)
Voltages (BE, CE)
Gain (Beta, Alpha)
Resistances
Formula for current (Ic = βIb; Ie = (1 + β)Ib)

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Description

This quiz covers the fundamentals of transistors, including types such as Bipolar Junction Transistors (BJTs) and Junction Field Effect Transistors (JFETs). It goes into detail about how these electronic components work, their structure, and their applications in amplifying and switching signals. Test your knowledge on the characteristics and functions of these crucial devices in electronics.