PN Junction Diode Quiz
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Questions and Answers

What happens during the positive half cycle of the input AC voltage in a centre tapped rectifier?

  • The diode D2 is forward biased while D1 is reverse biased.
  • Only the negative half cycle contributes to the load voltage.
  • The current flows through the circuit and D1 charges the capacitor to peak value. (correct)
  • The capacitor discharges through load resistance RL.

    • What is the effect of the capacitor in a centre tapped transformer full-wave rectifier circuit?

  • It increases the AC voltage across the load.
  • It acts to smooth the output by bypassing AC components. (correct)
  • It discharges instantly across the load during both half cycles.
  • It decreases the average DC value of the load current.

    • What happens to the voltage across the capacitor after it charges during the positive half cycle?

  • The voltage remains constant regardless of load.
  • It decreases exponentially with the time constant RL C. (correct)
  • It increases linearly with time until the next cycle.
  • It immediately drops to zero after the capacitor is charged.

    • During the negative half cycle of the input voltage, what state are the diodes in a centre tapped rectifier?

    <p>Diode D2 is forward biased, while D1 is reverse biased.</p> Signup and view all the answers

    What characterizes the load current in a rectifier circuit according to Fourier’s theorem?

    <p>The load current is unidirectional but fluctuating.</p> Signup and view all the answers

    What is the maximum current that a low current diode can typically handle?

    <p>100mA</p> Signup and view all the answers

    How does the depletion region behave in a forward-biased pn-junction?

    <p>It gets narrower.</p> Signup and view all the answers

    What happens to the built-in potential of a pn-junction in reverse bias?

    <p>It increases.</p> Signup and view all the answers

    What type of diode material is indicated by a dimensionless number η of 1?

    <p>Germanium</p> Signup and view all the answers

    In the equation I = Irs [e^(qV/(kB T)) - 1], what does Irs represent?

    <p>The reverse saturation current.</p> Signup and view all the answers

    What is the significance of the forward voltage threshold (Vf) in a pn-junction?

    <p>It allows majority charge carriers to flow across the junction.</p> Signup and view all the answers

    Which of the following can survive the largest reverse voltages?

    <p>High current diodes</p> Signup and view all the answers

    What role do the holes on the p side play in a reverse-biased pn-junction?

    <p>They are attracted to the negative terminal.</p> Signup and view all the answers

    What forms the depletion region in a pn-junction diode?

    <p>Recombination of holes and electrons</p> Signup and view all the answers

    What is the built-in potential Vbi for silicon (Si) in a pn junction diode?

    <p>0.7V</p> Signup and view all the answers

    Which type of current is caused by the concentration gradient in a pn junction diode?

    <p>Diffusion current</p> Signup and view all the answers

    Under steady state conditions, what is the relationship between drift current and diffusion current in a pn junction diode?

    <p>Drift current and diffusion current are equal</p> Signup and view all the answers

    What happens to a pn junction diode when it becomes reverse biased?

    <p>It blocks current flow and acts as an OFF switch</p> Signup and view all the answers

    What is the effect of a high level of forward current on a pn junction diode?

    <p>It can cause overheating and destroy the diode</p> Signup and view all the answers

    Which formula correctly describes the width of the depletion region Wdep in an open circuit pn junction?

    <p>$Wdep = rac{2ϵ(Vbi)}{q(NA + ND)}$</p> Signup and view all the answers

    What causes the electric field E in a pn junction diode?

    <p>Uncovering of bound charges</p> Signup and view all the answers

    What is the main function of the capacitor in a half wave rectifier circuit?

    <p>To store energy during the positive cycle.</p> Signup and view all the answers

    During which part of the input voltage cycle does the diode become reverse biased in a half wave rectifier?

    <p>From π/2 to π.</p> Signup and view all the answers

    What happens to the output waveform in a half wave rectifier with a capacitor filter?

    <p>It contains ripple defined by the voltage difference.</p> Signup and view all the answers

    In a full wave rectifier using a bridge circuit, which diodes are forward biased during the positive half cycle?

    <p>D2 and D4.</p> Signup and view all the answers

    What is a notable characteristic of the waveform produced by a full wave rectifier?

    <p>It has a higher average output voltage than a half wave rectifier.</p> Signup and view all the answers

    In a center tapped transformer full wave rectifier circuit, which diode is forward biased during the positive half cycle?

    <p>D1.</p> Signup and view all the answers

    How does the capacitor behave when the input voltage exceeds the capacitor voltage in a half wave rectifier?

    <p>The capacitor starts charging up to the maximum input voltage.</p> Signup and view all the answers

    What defines the ripple in the output voltage of a filtered half wave rectifier?

    <p>The difference between maximum and minimum voltages.</p> Signup and view all the answers

    What is the efficiency formula for a half wave rectifier?

    <p>$\eta = \frac{I_{dc}}{I_{m}} \cdot \frac{1}{\pi}$</p> Signup and view all the answers

    What is the peak inverse voltage (PIV) for a centre tapped transformer?

    <p>$P_{IV} = 2V_{m}$</p> Signup and view all the answers

    What characteristic does a positive series clipper exhibit?

    <p>It does not affect the negative half of the waveform.</p> Signup and view all the answers

    Which configuration uses the equation $P_{IV} = V_{m}$?

    <p>Half wave rectifier</p> Signup and view all the answers

    Calculate the efficiency of a full wave rectifier using the formula $\eta = \frac{I_{dc}}{I_{rms}}$.

    <p>0.810</p> Signup and view all the answers

    What happens when light is focused on the junction of a photodiode?

    <p>It produces free electrons and holes.</p> Signup and view all the answers

    In which scenario would a negative clamper be used?

    <p>To maintain a certain negative offset on the waveform.</p> Signup and view all the answers

    What is the effect of a biased clipper on a signal?

    <p>It creates a threshold that modifies specific segments of the signal.</p> Signup and view all the answers

    Study Notes

    PN Junction Diode

    • A pn junction diode is formed by joining a p-type and n-type semiconductor material.
    • Holes and electrons recombine at the junction, leaving behind uncovered bound charges which create a depletion region.
    • The depletion region is characterized by a potential barrier or built-in potential (Vbi), typically 0.7V for silicon and 0.3V for germanium.
    • An electric field exists across the junction due to the uncovered charges and depletion region.
    • Two types of current flow occur in pn junction diodes: diffusion current and drift current.
    • Diffusion current arises from the concentration gradient of charge carriers. Holes diffuse from the p-type to n-type, and electrons diffuse from the n-type to p-type.
    • Drift current is caused by the electric field across the junction. Holes drift from n-type to p-type, and electrons drift from p-type to n-type.
    • Under steady state, drift current equals diffusion current, resulting in zero net current in an open circuit.
    • The width of the depletion region (Wdep) in an open circuit pn junction is determined by the doping concentrations of the p and n regions.
    • A pn junction diode acts as a switch: ON when forward biased, and OFF when reverse biased.

    Diode Characteristics

    • The total current (I) flowing through a pn junction diode is described by the diode equation.
    • The equation includes the reverse saturation current (Irs), the electron charge (q), Boltzmann's constant (KB), temperature (T), and a dimensionless number (η).
    • Forward biased pn junction:
      • The depletion region width and built-in potential decrease.
      • Majority charge carriers move from one side to the other, resulting in current flow.
      • Significant forward current starts flowing when the applied voltage (Vf) exceeds the built-in potential (Vbi).
    • Reverse biased pn junction:
      • The depletion region width and built-in potential increase.
      • The junction acts as a high impedance to dc components, but low resistance to ac components.

    Diode Applications

    • Rectifiers: Devices used to convert alternating current (AC) to direct current (DC).
      • Half-wave rectification: Produces a single pulse of DC current per AC cycle.
      • Full-wave rectification: Uses a bridge or center-tapped transformer configuration to produce DC current for both positive and negative half-cycles of the AC input.
    • Filtering: Used to smooth out the ripple in the rectified DC output.
      • Capacitor filter: A capacitor connected in parallel with the rectifier output stores charge during the input voltage peaks and discharges during the valleys, reducing ripple.

    Rectifier Parameters

    • Average DC value (Idc): The average current flowing through the load in a rectifier circuit.
    • Rectification efficiency (η): The ratio of DC power (Pdc) to AC power (Pac) delivered to the load.
    • Peak inverse voltage (PIV): The maximum reverse voltage that the diode can withstand without breaking down.

    Diode Clipping and Clamping Circuits

    • Clipping circuits: Limit the output voltage to a specific level.
      • Can be positive or negative, series or parallel, and biased.
    • Clamping circuits: Shift the DC level of a signal without affecting its shape.
      • Can be positive or negative, and can be biased.

    Photodiode

    • A photodiode generates free electrons and holes by absorbing incident light.

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    Related Documents

    JUNCTION DIODES PDF

    Description

    Test your understanding of pn junction diodes, including their formation, characteristics, and the currents that flow through them. This quiz covers topics such as the depletion region, potential barriers, and the differences between diffusion and drift current. Challenge yourself to ensure a solid grasp of semiconductor principles!

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