V-I characteristics, Zener diode, voltage regulation, tunnel diode
## V-I Characteristics (10 MCQs)
1. In the V-I characteristics of a PN junction diode, the knee point represents:
a) Reverse breakdown
b) Forward conduction start
c) Zero bias
d) Saturation current
**Answer: b) Forward conduction start**
*Explanation: The knee or cut-in voltage is where current rises sharply in forward bias due to narrowing depletion region, around 0.7V for silicon.* [1]
2. Under reverse bias in V-I curve, current remains nearly constant up to breakdown because:
a) Majority carriers flow
b) Only minority carriers (saturation current) flow
c) Depletion widens
d) Barrier decreases
**Answer: b) Only minority carriers (saturation current) flow**
*Explanation: Reverse bias drifts minority carriers, producing small leakage current independent of voltage until breakdown.* [2]
3. Forward current in V-I characteristics is primarily due to:
a) Drift of minority carriers
b) Diffusion of majority carriers
c) Avalanche effect
d) Zener tunneling
**Answer: b) Diffusion of majority carriers**
*Explanation: Forward bias reduces barrier, allowing majority carriers to diffuse across junction.* [1]
4. The slope of V-I curve in forward bias indicates:
a) High resistance
b) Low dynamic resistance
c) Infinite resistance
d) Zero resistance
**Answer: b) Low dynamic resistance**
*Explanation: Steep slope shows diode behaves as low resistance path post-knee voltage.* [1]
5. At zero bias, V-I characteristic shows:
a) High forward current
b) Small diffusion current
c) Reverse saturation current
d) Breakdown
**Answer: b) Small diffusion current**
*Explanation: Few majority carriers overcome barrier, creating tiny current.* [1]
6. Reverse breakdown in V-I curve occurs due to:
a) Narrow depletion
b) Avalanche or Zener effect
c) Majority diffusion
d) Forward bias
**Answer: b) Avalanche or Zener effect**
*Explanation: High reverse voltage causes carrier multiplication or tunneling.* [2]
7. Silicon diode's forward knee voltage in V-I is about:
a) 0.2V
b) 0.7V
c) 1.1V
d) -0.7V
**Answer: b) 0.7V**
*Explanation: Barrier potential for silicon is ~0.7V where conduction begins.* [1]
8. V-I curve asymmetry shows diode is:
a) Linear device
b) Non-linear rectifier
c) Resistor
d) Capacitor
**Answer: b) Non-linear rectifier**
*Explanation: Conducts one way, blocks other, ideal for rectification.* [1]
9. In reverse bias quadrant of V-I, current is:
a) Exponential
b) Nearly zero (microamperes)
c) Linear
d) High
**Answer: b) Nearly zero (microamperes)**
*Explanation: Only minority carrier drift current flows.* [2]
10. Dynamic resistance from V-I slope is lowest in:
a) Reverse bias
b) Forward conduction
c) Zero bias
d) Breakdown
**Answer: b) Forward conduction**
*Explanation: Post-knee, small voltage change causes large current rise.* [1]
## Zener Diode (10 MCQs)
1. Zener diode operates in breakdown without damage due to:
a) Light doping
b) Heavy doping, narrow depletion
c) Forward bias only
d) Avalanche only
**Answer: b) Heavy doping, narrow depletion**
*Explanation: Heavy doping enables Zener or avalanche at precise voltage.* [3]
2. Zener breakdown occurs at:
a) High voltages (>5V)
b) Low voltages (<5V)
c) Forward bias
d) Zero bias
**Answer: b) Low voltages (<5V)**
*Explanation: Quantum tunneling in heavily doped junction at low reverse V.* [3]
3. In reverse bias, Zener maintains:
a) Constant current
b) Constant voltage
c) Increasing resistance
d) Zero current
**Answer: b) Constant voltage**
*Explanation: Breakdown voltage (Vz) stays fixed despite current changes.* [3]
4. Zener effect involves:
a) Carrier multiplication
b) Electron tunneling
c) Diffusion
d) Drift only
**Answer: b) Electron tunneling**
*Explanation: Electrons tunnel through narrow barrier in heavy doping.* [3]
5. Avalanche breakdown in Zener is for:
a) Low Vz
b) High Vz (>5V)
c) Forward
d) No bias
**Answer: b) High Vz (>5V)**
*Explanation: Impact ionization multiplies carriers at higher voltages.* [3]
6. Zener symbol differs by:
a) Arrow
b) Bent lines at cathode
c) Circle
d) Dot
**Answer: b) Bent lines at cathode**
*Explanation: Indicates reverse breakdown operation.* [3]
7. Minimum Zener current for regulation is:
a) Iz max
b) Iz min (knee current)
c) If
d) Zero
**Answer: b) Iz min (knee current)**
*Explanation: Below Iz min, voltage regulation fails.* [4]
8. Zener doping is:
a) Light p, heavy n
b) Heavily both sides
c) Light both
d) Heavy p, light n
**Answer: b) Heavily both sides**
*Explanation: Creates thin depletion for sharp breakdown.* [3]
9. Zener forward behaves like:
a) Regular diode
b) Open circuit
c) Resistor
d) Capacitor
**Answer: a) Regular diode**
*Explanation: Conducts normally in forward bias.* [3]
10. Breakdown mechanism depends on:
a) Temperature only
b) Doping level
c) Size
d) Shape
**Answer: b) Doping level**
*Explanation: Heavy doping favors Zener, lighter favors avalanche.* [3]
## Voltage Regulation (10 MCQs)
1. Zener regulator uses diode in:
a) Forward bias
b) Reverse breakdown
c) Zero bias
d) Series
**Answer: b) Reverse breakdown**
*Explanation: Maintains constant Vz across load despite Vin changes.* [4]
2. Series resistor in Zener regulator limits:
a) Load current
b) Zener current
c) Output voltage
d) Input power
**Answer: b) Zener current**
*Explanation: Prevents excess Iz beyond max rating.* [4]
3. Voltage regulation formula: %VR =
a) (Vnl - Vfl)/Vfl *100
b) (Vnl - Vfl)/Vnl *100
c) (Vfl - Vnl)/Vnl *100
d) Vnl/Vfl
**Answer: b) (Vnl - Vfl)/Vnl *100**
*Explanation: Measures no-load to full-load voltage drop percentage.* [5]
4. For regulation, load current range: IL max =
a) Iz min - Iz max
b) (Vin - Vz)/Rs - Iz min
c) Iz max
d) Zero
**Answer: b) (Vin - Vz)/Rs - Iz min**
*Explanation: Ensures Iz stays between min and max.* [4]
5. Shunt regulator configuration has Zener:
a) Series with load
b) Parallel to load
c) Before Rs
d) After load
**Answer: b) Parallel to load**
*Explanation: Excess current shunts through Zener.* [4]
6. Regulation improves with:
a) High Zener dynamic resistance
b) Low Zener dynamic resistance
c) No Rs
d) High load
**Answer: b) Low Zener dynamic resistance**
*Explanation: Sharper Vz constancy.* [5]
7. Iz max determines:
a) Min Rs
b) Max Rs
c) Load max
d) Vin min
**Answer: a) Min Rs**
*Explanation: Rs >= (Vin max - Vz)/Iz max.* [4]
8. Poor regulation if load current < :
a) Iz max
b) Iz min
c) IL max
d) Zero
**Answer: b) Iz min**
*Explanation: Zener leaves breakdown region.* [4]
9. In regulator, cathode connects to:
a) Ground
b) Positive supply
c) Load negative
d) Rs end
**Answer: b) Positive supply**
*Explanation: Reverse biases Zener.* [3]
10. % Regulation ideal is:
a) High
b) Zero
c) Negative
d) 50%
**Answer: b) Zero**
*Explanation: Constant output voltage.* [5]
## Tunnel Diode (10 MCQs)
1. Tunnel diode exhibits:
a) Positive resistance only
b) Negative differential resistance
c) Zero resistance
d) Infinite resistance
**Answer: b) Negative differential resistance**
*Explanation: Current decreases with voltage increase in region.* [3]
2. Tunnel diode works on:
a) Diffusion
b) Quantum tunneling
c) Avalanche
d) Drift
**Answer: b) Quantum tunneling**
*Explanation: Electrons tunnel through thin barrier.* [6]
3. Depletion in tunnel diode is thin due to:
a) Light doping
b) Heavy doping, abrupt junction
c) Long life
d) High temp
**Answer: b) Heavy doping, abrupt junction**
*Explanation: Allows tunneling at low V.* [6]
4. Material for tunnel diode is usually:
a) Silicon
b) Germanium
c) GaAs
d) All
**Answer: b) Germanium**
*Explanation: Best tunneling properties.* [6]
5. Used in:
a) Low freq
b) Microwave oscillators/amplifiers
c) Power supply
d) LED
**Answer: b) Microwave oscillators/amplifiers**
*Explanation: Negative resistance enables oscillation.* [6]
6. In forward bias, fermi level:
a) P lower than N
b) P higher than N initially
c) Equal
d) Irrelevant
**Answer: b) P higher than N initially**
*Explanation: Enables valence to conduction band tunneling.* [6]
7. Negative resistance region allows:
a) Rectification
b) Oscillation
c) Regulation
d) Clamping
**Answer: b) Oscillation**
*Explanation: With LC, generates high freq.* [3]
8. Peak to valley current ratio high in:
a) Poor tunnel diodes
b) Good ones
c) Zener
d) PN regular
**Answer: b) Good ones**
*Explanation: Sharp NDR characteristic.* [7]
9. Tunneling from:
a) N conduction to P conduction
b) N conduction to P valence
c) P valence to N conduction
d) Both b and c
**Answer: b) N conduction to P valence**
*Explanation: Band overlap due to heavy doping.* [6]
10. Frequency range:
a) Audio
b) Microwave
c) DC only
d) RF low
**Answer: b) Microwave**
*Explanation: Low capacitance, fast switching.* [6]
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