The load voltage in a Zener regulator remains constant if

 

551️⃣

Q: The ideal diode has which characteristic?
Options:
A) Zero forward resistance, infinite reverse resistance
B) Infinite forward resistance, zero reverse resistance
C) Both resistances finite
D) Both resistances infinite
Answer: A) Zero forward resistance, infinite reverse resistance
Explanation:
An ideal diode conducts perfectly in forward direction and blocks completely in reverse.

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552️⃣

Q: The forward voltage drop across an ideal diode is
Options:
A) 0 V
B) 0.7 V
C) 0.3 V
D) 1.1 V
Answer: A) 0 V
Explanation:
In ideal conditions, a diode behaves as a perfect short circuit when forward biased.

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553️⃣

Q: The reverse current in a real diode is due to
Options:
A) Majority carriers
B) Minority carriers
C) Thermal runaway
D) None
Answer: B) Minority carriers
Explanation:
In reverse bias, only minority carriers contribute to the small leakage current.

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554️⃣

Q: In forward bias, the potential barrier
Options:
A) Increases
B) Decreases
C) Remains constant
D) Becomes zero
Answer: B) Decreases
Explanation:
Applied forward voltage reduces the built-in potential barrier, allowing current flow.

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555️⃣

Q: The dynamic resistance of a diode is
Options:
A) Constant
B) Inversely proportional to current
C) Directly proportional to current
D) Independent of bias
Answer: B) Inversely proportional to current
Explanation:
Dynamic resistance $r_d = \frac{nV_T}{I_D}$; as current increases, resistance decreases.

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556️⃣

Q: The small-signal resistance of a diode at 25°C carrying 1 mA current is
Options:
A) 25 Ω
B) 26 Ω
C) 30 Ω
D) 40 Ω
Answer: B) 26 Ω
Explanation:
$r_d = V_T / I_D = 26\text{mV}/1\text{mA} = 26\ \Omega$.

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557️⃣

Q: The reverse saturation current of a diode
Options:
A) Doubles for every 10°C rise
B) Halves for every 10°C rise
C) Constant with temperature
D) Increases linearly
Answer: A) Doubles for every 10°C rise
Explanation:
Leakage current increases exponentially with temperature.

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558️⃣

Q: The transition capacitance of a diode is significant in
Options:
A) Forward bias
B) Reverse bias
C) No bias
D) Breakdown region
Answer: B) Reverse bias
Explanation:
Transition (junction) capacitance is prominent under reverse bias due to depletion width variation.

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559️⃣

Q: Diffusion capacitance occurs in
Options:
A) Forward bias
B) Reverse bias
C) Zero bias
D) None
Answer: A) Forward bias
Explanation:
Diffusion capacitance arises from stored charge of injected carriers under forward bias.

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560️⃣

Q: The value of thermal voltage $V_T$ at 25°C is
Options:
A) 0.025 V
B) 0.026 V
C) 0.03 V
D) 0.04 V
Answer: B) 0.026 V
Explanation:
$V_T = kT/q = 26 \text{mV}$ approximately at room temperature.

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561️⃣

Q: The diode current equation is given by
Options:
A) $I = I_S (e^{V/V_T} - 1)$
B) $I = I_S e^{-V/V_T}$
C) $I = V/R$
D) $I = I_S + V_T/V$
Answer: A) $I = I_S (e^{V/V_T} - 1)$
Explanation:
This is the Shockley diode equation.

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562️⃣

Q: In the diode equation, $I_S$ represents
Options:
A) Forward current
B) Reverse saturation current
C) Peak current
D) Leakage power
Answer: B) Reverse saturation current
Explanation:
$I_S$ is the very small current flowing due to minority carriers under reverse bias.

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563️⃣

Q: A half-wave rectifier conducts for
Options:
A) 180°
B) 90°
C) 360°
D) 270°
Answer: A) 180°
Explanation:
It conducts only during one half-cycle of the AC input.

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564️⃣

Q: The maximum efficiency of a half-wave rectifier is
Options:
A) 40.6%
B) 81.2%
C) 50%
D) 25%
Answer: A) 40.6%
Explanation:
$\eta = 0.406$ or 40.6% for half-wave rectifier.

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565️⃣

Q: In a full-wave rectifier, conduction occurs for
Options:
A) 180°
B) 360°
C) 90°
D) 270°
Answer: B) 360°
Explanation:
Both halves of the AC waveform are used for conduction.

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566️⃣

Q: The maximum efficiency of a full-wave rectifier is
Options:
A) 40.6%
B) 81.2%
C) 100%
D) 90%
Answer: B) 81.2%
Explanation:
Twice that of half-wave due to utilization of both halves of AC input.

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567️⃣

Q: Ripple frequency in a full-wave rectifier is
Options:
A) Same as input frequency
B) Twice the input frequency
C) Half the input frequency
D) Zero
Answer: B) Twice the input frequency
Explanation:
Output contains double frequency ripples since both halves are rectified.

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568️⃣

Q: The average DC output voltage of a full-wave rectifier is
Options:
A) $0.318V_m$
B) $0.637V_m$
C) $0.707V_m$
D) $1.414V_m$
Answer: B) $0.637V_m$
Explanation:
DC component = $\frac{2V_m}{\pi} = 0.637V_m$.

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569️⃣

Q: The peak inverse voltage (PIV) across each diode in a center-tap rectifier is
Options:
A) $V_m$
B) $2V_m$
C) $V_m/2$
D) $V_{rms}$
Answer: B) $2V_m$
Explanation:
Each diode must withstand twice the peak input voltage when reverse-biased.

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570️⃣

Q: The main advantage of a bridge rectifier over center-tap is
Options:
A) Less PIV
B) Higher efficiency
C) No center-tap transformer required
D) All of these
Answer: D) All of these
Explanation:
Bridge rectifier requires only $V_m$ PIV per diode and no center-tap winding.

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571️⃣

Q: The ripple factor of a full-wave rectifier is
Options:
A) 1.21
B) 0.482
C) 0.707
D) 0.31
Answer: B) 0.482
Explanation:
Ripple factor $r = \frac{V_{rms,ac}}{V_{dc}} = 0.482$.

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572️⃣

Q: A capacitor filter in a rectifier circuit
Options:
A) Increases ripple
B) Reduces ripple
C) Increases average current
D) Blocks DC
Answer: B) Reduces ripple
Explanation:
It charges at peaks and discharges slowly, smoothing the output.

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573️⃣

Q: The time constant RC of a filter should be
Options:
A) Large compared to input period
B) Small compared to input period
C) Equal to input period
D) Zero
Answer: A) Large compared to input period
Explanation:
A large RC constant provides better filtering with minimal ripple.

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574️⃣

Q: The purpose of a clipper circuit is
Options:
A) To limit voltage
B) To amplify signal
C) To filter DC
D) To integrate signal
Answer: A) To limit voltage
Explanation:
Clippers “clip” portions of the signal above or below a specified level.

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575️⃣

Q: The purpose of a clamper circuit is
Options:
A) To shift DC level
B) To limit amplitude
C) To amplify
D) To attenuate
Answer: A) To shift DC level
Explanation:
Clampers add or subtract a DC component without changing signal shape.

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576️⃣

Q: The load current in a half-wave rectifier with $R_L = 1kΩ$ and $V_m = 20V$ is
Options:
A) 6.37 mA
B) 12.7 mA
C) 20 mA
D) 25 mA
Answer: A) 6.37 mA
Explanation:
$I_{dc} = 0.318 V_m / R_L = 0.318×20/1000 = 6.36 mA$.

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577️⃣

Q: Zener diode regulation works when diode is
Options:
A) Forward biased
B) Reverse biased in breakdown region
C) Unbiased
D) Reverse biased below breakdown
Answer: B) Reverse biased in breakdown region
Explanation:
Zener maintains constant voltage across it once breakdown occurs.

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578️⃣

Q: Zener voltage remains constant because
Options:
A) Avalanche effect compensates current
B) Voltage drop independent of current
C) Depletion region adjusts dynamically
D) All of these
Answer: D) All of these
Explanation:
The Zener maintains constant voltage through dynamic breakdown mechanisms.

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579️⃣

Q: A 6V Zener diode in series with 220Ω resistor across 12V supply carries how much current?
Options:
A) 20 mA
B) 25 mA
C) 27 mA
D) 30 mA
Answer: B) 25 mA
Explanation:
$I = (12−6)/220 = 27.3mA \approx 25mA$.

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580️⃣

Q: The load voltage in a Zener regulator remains constant if
Options:
A) Load current changes
B) Supply voltage changes
C) Both A and B
D) None
Answer: C) Both A and B
Explanation:
Zener compensates both load and supply variations within limits.