Elements of Electronics - Summer 2022 Exam
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Questions and Answers

What is the primary purpose of a rectifier in an electronics circuit?

  • To step up voltage levels
  • To filter DC output
  • To convert AC power source to DC power source (correct)
  • To amplify AC signals

    • Which transformer type is typically used before a rectifier to reduce AC voltage?

  • Auto transformer
  • Isolation transformer
  • Step down transformer (correct)
  • Step up transformer

    • Which type of rectifier uses two diodes and a center tapped transformer?

  • Full wave rectifier (correct)
  • Zener rectifier
  • Bridge rectifier
  • Half wave rectifier

    • What is the output voltage of the IC 7824?

    <p>+24 V (C)</p> Signup and view all the answers

    What type of diode is most suitable for a voltage regulator circuit?

    <p>Zener diode (C)</p> Signup and view all the answers

    Which of the following statements accurately describes a Zener diode?

    <p>It regulates voltage across it in the reverse bias region. (D)</p> Signup and view all the answers

    What voltage does the IC 7906 output?

    <p>-6 V (D)</p> Signup and view all the answers

    Which rectifier type most efficiently converts AC to DC by utilizing four diodes?

    <p>Full wave bridge rectifier (C)</p> Signup and view all the answers

    What is the term used to describe the current that flows in the nano Ampere range due to minority carriers in a diode?

    <p>Reverse saturation current (D)</p> Signup and view all the answers

    Which mechanism is NOT a type of diode breakdown?

    <p>Thermal breakdown (A)</p> Signup and view all the answers

    The reverse breakdown voltage is defined as?

    <p>The reverse voltage at which large reverse current flows (A)</p> Signup and view all the answers

    In a half wave rectifier with LC filter, what is the preferred filter for high load resistance?

    <p>Capacitor input filter (D)</p> Signup and view all the answers

    What component is used to maintain continuous current through the filter inductance in a half wave rectifier circuit?

    <p>Bleeder resistor (B)</p> Signup and view all the answers

    During the positive half cycle of an AC supply, what happens to the diode in the half wave rectifier?

    <p>The diode conducts for the entire positive cycle (B)</p> Signup and view all the answers

    What is the initial assumption about the voltage on the capacitor in a half wave rectifier before the diode starts conducting?

    <p>It is zero (C)</p> Signup and view all the answers

    What happens to the capacitor after the peak value of the secondary input voltage in a half wave rectifier?

    <p>It begins to discharge slowly (B)</p> Signup and view all the answers

    What is the primary difference in the factors affecting frequency of oscillations between an RC oscillator and an LC oscillator?

    <p>RC oscillators depend on the values of resistance and capacitance, while LC oscillators depend on the values of resistance and inductance. (D)</p> Signup and view all the answers

    Which of the following is not a characteristic of an RC oscillator?

    <p>Dependent on the values of R &amp; L (A)</p> Signup and view all the answers

    What is a common application for LC oscillators?

    <p>Frequency synthesizer in communication devices (C)</p> Signup and view all the answers

    During which clock edge does the slave flip flop toggle in a setup where J = K = 1?

    <p>At the negative edge of the clock pulse (D)</p> Signup and view all the answers

    Which of the following statements best describes the frequency stability of RC oscillators?

    <p>They have poor frequency stability except for the Hartley oscillator. (B)</p> Signup and view all the answers

    What is the typical knee voltage value for a Silicon diode?

    <p>0.6V (D)</p> Signup and view all the answers

    What component in the IC 723 serves as a fixed voltage reference?

    <p>Temperature compensated zener diode (C)</p> Signup and view all the answers

    What is the common knee voltage for a Germanium diode?

    <p>0.2V (A)</p> Signup and view all the answers

    What is the primary purpose of rectifiers in electronic circuits?

    <p>To convert AC to DC (B)</p> Signup and view all the answers

    Which component controls the series pass transistor in the IC 723?

    <p>Error amplifier (B)</p> Signup and view all the answers

    What role does the frequency compensation terminal play in the operation of the IC 723?

    <p>Controls frequency response of the error amplifier (B)</p> Signup and view all the answers

    Which of the following is NOT a type of rectifier?

    <p>Phase-locked rectifier (B)</p> Signup and view all the answers

    How many marks are allotted for stating the need of rectifiers and listing their types?

    <p>1 Mark (D)</p> Signup and view all the answers

    The series pass transistor in the IC 723 is designed to handle what approximate power dissipation?

    <p>800 mW (B)</p> Signup and view all the answers

    Which aspect of a candidate's answer is emphasized more when assessing their understanding?

    <p>Key words (D)</p> Signup and view all the answers

    How is voltage from the regulated output used in the IC 723’s functionality?

    <p>It is compared to the reference potential by the error amplifier. (B)</p> Signup and view all the answers

    How can credit be given for numerical problems during assessment?

    <p>Step-wise based on the workings shown (D)</p> Signup and view all the answers

    What function do the scaling resistors perform in the IC 723?

    <p>Control the reference voltage multiplication. (B)</p> Signup and view all the answers

    What is the significance of drawing figures in answers?

    <p>Credit may be given for principal components indicated (D)</p> Signup and view all the answers

    What is the main purpose of transistor Q2 in the IC 723?

    <p>To function as a current limiter. (D)</p> Signup and view all the answers

    What determines the fixed point operation of the zener diode in the IC 723?

    <p>The current supplied by the constant current source. (B)</p> Signup and view all the answers

    What is the formula to calculate the current gain beta ($\beta$) of a transistor?

    <p>$\beta = \frac{I_C}{I_B}$ (D)</p> Signup and view all the answers

    In the context of a Colpitt's oscillator, which component is essential for generating oscillations?

    <p>Transistor (B)</p> Signup and view all the answers

    What does the alpha ($\alpha$) of a transistor represent?

    <p>The ratio of collector current to emitter current (B)</p> Signup and view all the answers

    Which of the following statements is true about light emitting diodes (LEDs)?

    <p>LEDs emit light when electrons recombine with holes in a semiconductor. (A)</p> Signup and view all the answers

    What is one of the basic requirements for constructing a bridge rectifier?

    <p>Four diodes (A)</p> Signup and view all the answers

    What is the primary function of a π filter in rectification circuits?

    <p>To smooth out the output voltage (B)</p> Signup and view all the answers

    What is the correct relationship between alpha ($\alpha$) and beta ($\beta$) in a transistor?

    <p>$\alpha = \frac{\beta}{\beta + 1}$ (C)</p> Signup and view all the answers

    What type of semiconductor layers are involved in the construction of a light-emitting diode (LED)?

    <p>N-type, P-type, and an active region (B)</p> Signup and view all the answers

    Flashcards

    Knee voltage of Silicon diode

    The voltage at which a silicon diode begins to conduct significantly.

    Knee voltage of Germanium diode

    The voltage at which a germanium diode begins to conduct significantly.

    Rectifier purpose

    Devices that convert alternating current (AC) to direct current (DC).

    Types of rectifiers

    Different circuits designed to convert AC to DC, including half-wave and full-wave rectifiers.

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    Silicon diode

    A type of diode made from silicon.

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    Germanium diode

    A semiconductor device allowing current to flow primarily in one direction.

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    Alternating Current (AC)

    Electrical current that reverses its direction periodically.

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    Direct Current (DC)

    Electrical current flowing consistently in one direction.

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    Rectifier function

    Converts AC (alternating current) to DC (direct current) power.

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    Half-wave rectifier

    A type of rectifier that uses only one half of the AC cycle to produce DC.

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    Full-wave rectifier

    A type of rectifier that uses both half of the AC cycle to produce DC.

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    7824 IC

    A positive voltage regulator IC providing a constant +24V output.

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    7906 IC

    A negative voltage regulator IC providing a constant -6V output.

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    Zener Diode use in voltage regulators

    Zener diodes are crucial components for creating stable voltage outputs.

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    PNP transistor

    A type of bipolar junction transistor (BJT) that has a positive base compared to emitter.

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    NPN transistor

    A type of bipolar junction transistor (BJT) that has a negative base compared to emitter.

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    Reverse Saturation Current

    A very small current flowing in a diode due to minority carriers, typically measured in nanoamperes for silicon.

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    Reverse Breakdown Voltage

    The reverse voltage at which a diode's reverse current increases drastically.

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    Avalanche Breakdown

    One mechanism by which a diode breaks down due to high reverse voltage.

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    Zener Breakdown

    Another mechanism for diode breakdown due to high reverse voltage.

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    Breakover Voltage

    The minimum voltage where a diode's forward current increases dramatically.

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    LC Filter

    A filter circuit (inductors and capacitors) used to smooth out the pulsating DC in half-wave rectifiers.

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    Bleeder Resistor

    A resistor used to maintain a continuous current through a filter inductance (in half-wave rectifiers).

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    IC 723 Functional Block

    IC 723 is a voltage regulator with blocks for reference voltage (using a temperature-compensated zener diode and a constant current source), error amplifier, and series pass transistor.

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    Reference Element (IC 723)

    The part of the IC 723 that creates and maintains a stable reference voltage, crucial for regulating the output.

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    Error Amplifier (IC 723)

    A high-gain amplifier in IC 723 that compares the regulated output voltage with the reference voltage, providing an error signal.

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    Series Pass Transistor (IC 723)

    A transistor in IC 723 that adjusts the current through the output, allowing for voltage regulation.

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    Frequency Compensation (IC 723)

    A part of the IC 723 that controls the frequency response of the error amplifier, preventing oscillations.

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    Voltage Regulation

    The process of maintaining a constant output voltage despite changes in input voltage or load.

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    Constant Current Source

    A component in the IC 723 that ensures a constant current flows through the zener diode, thereby maintaining a stable reference voltage.

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    Short Circuit Protection (IC 723)

    The IC 723 includes a current limiter to protect it from short circuits. This is accomplished by the transistor Q2.

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    Master-Slave Flip-Flop

    A type of flip-flop that uses two separate flip-flops, a master and a slave, to achieve edge-triggered behavior. The master flip-flop changes state on the clock's positive edge, while the slave flip-flop changes state on the clock's negative edge.

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    RC Oscillator

    An electronic circuit that generates oscillations using a resistor (R) and a capacitor (C). These oscillations are typically used in applications requiring low and medium frequencies, such as signal generation.

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    LC Oscillator

    An electronic circuit that generates oscillations using an inductor (L) and a capacitor (C). These oscillations are typically used in applications requiring high frequencies, such as radio and TV.

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    Common Base Configuration

    A transistor configuration where the base is common to both the input and output. This configuration is characterized by high input impedance and low output impedance.

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    Input and Output Characteristics of Common Base Configuration

    The input characteristics show the relationship between the base current (IB) and the emitter-base voltage (VBE) at different values of collector-base voltage (VCB). The output characteristics show the relationship between the collector current (IC) and the collector-emitter voltage (VCE) at different values of emitter current (IE).

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    Colpitt's Oscillator

    A type of electronic oscillator circuit that uses a tapped capacitor to create feedback and generate an oscillating signal.

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    Bridge Rectifier

    A rectifier circuit using four diodes arranged in a bridge configuration to convert AC to DC.

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    Transistor Current Gain (β)

    The ratio of collector current (IC) to base current (IB) in a transistor, representing the amplification factor.

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    Transistor Current Gain (α)

    The ratio of collector current (IC) to emitter current (IE) in a transistor, representing the efficiency of current transfer.

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    LED Construction

    LEDs consist of three layers: an n-type semiconductor, a p-type semiconductor, and an active region. When current flows, electrons and holes recombine in the active region, emitting light.

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    LED Application

    LEDs are used in a wide range of applications like displays, lighting, indicators, automotive lights, and communication devices.

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    Active Region

    The region within an LED where electrons and holes recombine, releasing photons (light) as a result.

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    Study Notes

    Important Instructions to Examiners

    • Answers should be assessed based on key words, not just verbatim matches to the model answer.
    • Examiners should evaluate candidate understanding, allowing for variations in wording and language.
    • Grammatical or spelling errors should not significantly impact marks (except in English and Communication Skills subjects).
    • Figures should be assessed based on principal components, not exact drawings.
    • Numerical problems should be graded step-by-step.
    • Minor variations in assumed constant values or calculations should be considered acceptable.

    Elements of Electronics - Summer 2022 Examination - Model Answer

    • Question 1: Attempt any five of the following.

      • Knee Voltage for Diodes: Silicon diodes have a knee voltage of 0.6V, and germanium diodes have a knee voltage of 0.2V.
      • Rectifier Need: Rectifiers are needed to convert AC power to DC power, used in circuits like amplifiers. A step-down transformer reduces AC voltage to a usable level before rectification occurs.

    • Question 1 (Continued):

      • Diode Types: Half-wave rectifiers, full-wave rectifiers, and full-wave rectifiers with center tap transformers, full-wave bridge rectifiers.

    • Question 2 (c): Draw symbols for PNP and NPN transistors.

      • Transistor symbols should be accurate to the standard representation.

    • Question 2 (d): IC 7824 output voltage = +24V, IC 7906 output voltage = +6V. (Positive/Negative voltage regulators)

    • Question 2 (e): Suitable diode type for voltage regulator = Zener diode.

    • Question 2 (f): Line Regulation: The change in regulated load voltage due to change in line voltage. Line regulation= (VLH -VLL)/VLL where VLH = Load voltage with high line voltage and VLL = Load voltage with low line voltage.

      -Load Regulation: The change in output voltage when the load current changes. Load regulation = (VNL - VFL) / VNL where VNL= output voltage on no load and VFL = Output voltage on full load.

    • Question 2 (g): Draw the symbol and truth table for an Ex-OR gate (Include input and output columns with binary values).

    • Question 3 (a): Describe V-I characteristics of a P-N junction diode and define:

      • Breakover Voltage: The minimum forward voltage where the barrier potential breaks and forward current rapidly increases.
      • Reverse Breakdown Voltage: The reverse voltage at which junction breakdown occurs and reverse current significantly increases.

    • Question 4 (a): Explain the working of (Half-wave rectifier with LC filer) with a circuit diagram.

      • The LC filter is a combination of an inductor (L) in series and capacitor (C) in parallel to the load resistor.

    • Question 4 (b): Explain the working of half-wave rectifier with a circuit diagram involving a capacitor and an inductor.

    • Question 5: Transistor as a switch: Explain the properties of a transistor acting as a switch when in cutoff and saturation region. Depict input and output waveforms when acting as a switch.

    • Question 6 (d): Block Diagram of a regulated DC power supply (Includes AC mains transformer, rectifier circuit, filter circuit, and voltage regulator).

    • Question 6 (c): Functional block diagram of IC 723 (Details about temperature compensated zener diode, constant current source, and reference amplifier which compose the reference element).

    • Question 7 (b): Explain the working of a crystal oscillator. Include a diagram.

    • Question 7 (c): Transistor configurations (CB, CE, CC) and four applications of BJTs as amplifiers, switches, oscillators, and other components in electronic systems.

    • Question 8 (d): Compare half-wave, full-wave center-tapped, and full-wave bridge rectifiers in terms of ripple factor, rectification efficiency, and peak inverse voltage (PIV).

    • Question 9 (a): Describe Barkhausen criteria and draw the Colpitt oscillator circuit.

    • Question 10 (b): Draw circuit diagram of a bridge rectifier with a π-filter (pi-filter). Include input and output waveforms (show AC input and output voltage).

    • Question 10 (c): Given IB and IC values for a transistor, calculate α and β. (α is the common-emitter current amplification factor; β is the common-base current amplification factor).

    • Question 10 (d): Explain construction and application of LED. Explain light emission, give a diagram of an LED showing light emission mechanism.

    • Question 11 (a): Given a transistor's β and collector current, determine base current and emitter current.

    • Question 11 (b): Calculate the input voltage range for a Zener diode voltage regulator circuit given specific values for currents and resistances.

    • Question 12 (c): Explain the disadvantage of J-K flip-flop. Explain operation of MS J-K flip-flop with diagram. (Including Master and Slave sections)

    • Question 12 (a): Explain comparison between RC and LC oscillators. Include circuit diagrams (Include six comparative points).

    • Question 13: (Input/Output characteristics) Sketch the input characteristics for common base configuration for two different values of VCB, and output characteristics for two different values of IE for NPN transistor. Calculate input and output resistances.

    • Question 13 (c): Convert given decimal, hexadecimal, and octal numbers to their binary representations.

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    Elements of Electronics - 2022 Summer Exam - Model Answer PDF

    Description

    Test your understanding of key concepts in electronics with this quiz focusing on diode knee voltage and the necessity of rectifiers. Demonstrate your knowledge of AC to DC conversion and the use of transformers in electronic circuits. Prepare now to excel in your examination!

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