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Difficulty: MediumDiodes

In a basic power supply circuit, an alternating current (AC) source is connected in series with a single PN-junction diode and a resistive load. Which of the following best describes the waveform and polarity of the voltage developed across the load resistor?

  1. A
    Continuous direct current (DC) that maintains a constant, ripple-free voltage level across both halves of the input cycle
  2. B
    Alternating current (AC) that flows in both directions with reduced amplitude across both halves of the cycle
  3. Pulsating direct current (DC) that appears only during the half-cycles when the diode is forward-biasedAnswer
  4. D
    Alternating voltage that is amplified into high-frequency oscillations by converting current into magnetic energy

Answer

Pulsating direct current (DC) that appears only during the half-cycles when the diode is forward-biased
A standard PN-junction diode conducts current only when it is forward-biased (anode more positive than cathode) and prevents current flow when reverse-biased. In an AC circuit, this unidirectional conduction allows current to pass through the load during only one half of each alternating cycle, converting the bidirectional AC input into a pulsating direct current (DC) output.

Step-by-Step Solution

1
Analyze the one-way conduction property of the PN-junction diode.
The diode allows current to pass only when its anode is positive relative to its cathode (forward bias) and blocks current when polarity reverses (reverse bias).
Semiconductor PN junctions function as directional electrical check valves.
2
Evaluate the circuit response across both halves of the sinusoidal AC cycle.
During the positive half-cycle, the diode conducts and produces a voltage across the load resistor; during the negative half-cycle, the diode blocks conduction, dropping current to zero.
This process constitutes half-wave rectification.
3
Classify the resulting load voltage waveform.
The voltage across the load is unidirectional and periodic, known as pulsating DC.
Because current flows in only one direction in pulses without filter smoothing, the output is pulsating DC.

Key Concept

Diode rectification and unidirectional current conduction
Estimated Time:1m 0s
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Topics

Diodes

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