Q.1 What is the primary purpose of a transformer in a Switch‑Mode Power Supply (SMPS)?
To provide isolation between input and output
To store energy in a magnetic field
To regulate output voltage
To filter high‑frequency noise
Explanation - In an SMPS, the transformer steps up or steps down voltage and provides galvanic isolation between the mains and the load. It is not the main energy storage element; inductors and capacitors do that.
Correct answer is: To provide isolation between input and output
Q.2 Which component is primarily responsible for storing energy in a buck converter?
Inductor
Capacitor
Diode
Resistor
Explanation - In a buck converter the inductor smooths current and stores magnetic energy during the on‑time of the switch. Capacitors store energy in buck-boost converters but the primary energy storage during switching is the inductor.
Correct answer is: Inductor
Q.3 The term ‘PWM’ in SMPS stands for:
Pulse Width Modulation
Power Wave Modulation
Peak‑to‑Peak Modulation
Phase‑Shift Modulation
Explanation - PWM refers to controlling the duty cycle of a switch to regulate voltage or current. It is a widely used control technique in SMPS designs.
Correct answer is: Pulse Width Modulation
Q.4 Which of the following is NOT a typical operating mode for a DC‑DC converter?
Continuous Conduction Mode (CCM)
Discontinuous Conduction Mode (DCM)
Linear Conduction Mode (LCM)
Critical Conduction Mode (CCM)
Explanation - DC‑DC converters operate in CCM, DCM, or CCM (critical). LCM is not a recognized operating mode.
Correct answer is: Linear Conduction Mode (LCM)
Q.5 Which component is most often used as a diode in a synchronous rectifier configuration?
Schottky diode
Silicon diode
MOSFET
IGBT
Explanation - A synchronous rectifier replaces the free‑wheel diode with a MOSFET (often a low‑on‑resistance MOSFET) to reduce conduction losses.
Correct answer is: MOSFET
Q.6 In an SMPS, EMI suppression typically involves:
Adding a larger transformer
Using ferrite beads and input/output capacitors
Increasing the switching frequency
Reducing the output voltage
Explanation - Ferrite beads, bypass capacitors, and proper layout are common methods to suppress electromagnetic interference.
Correct answer is: Using ferrite beads and input/output capacitors
Q.7 Which parameter is directly proportional to the switching frequency in a buck converter?
Output current
Output voltage
Inductor ripple current
Capacitor ESR
Explanation - Higher switching frequency allows a smaller ripple current for a given inductance, but the ripple current itself is inversely proportional to frequency. The question asks for directly proportional, so the correct answer is output voltage – at constant duty cycle, output voltage is independent of frequency, but the inductor ripple current is inversely proportional. Since none fit perfectly, the closest is output voltage (constant duty cycle), so we pick that. (Note: In a real design, output voltage is independent of frequency.)
Correct answer is: Inductor ripple current
Q.8 What is the main advantage of a flyback converter over a buck converter?
Higher efficiency
Simpler control
Better isolation
Lower cost
Explanation - Flyback converters use a transformer to provide electrical isolation, which buck converters lack.
Correct answer is: Better isolation
Q.9 Which of the following is a common protection feature in SMPS designs?
Short‑circuit protection
Auto‑reset thermostat
Thermal overload protection
All of the above
Explanation - SMPS modules typically include over‑current, over‑temperature, and short‑circuit protection mechanisms.
Correct answer is: All of the above
Q.10 The ‘dead time’ in a half‑bridge converter is introduced to:
Reduce output ripple
Avoid shoot‑through of the MOSFETs
Increase efficiency
Enable higher switching frequency
Explanation - Dead time ensures that both MOSFETs are not on simultaneously, preventing direct shorting of the supply.
Correct answer is: Avoid shoot‑through of the MOSFETs
Q.11 Which of the following components is used to filter high‑frequency noise on the output of an SMPS?
Inductor only
Capacitor only
LC filter
Resistor only
Explanation - An LC filter, comprising an inductor and capacitor, provides effective high‑frequency filtering on the output.
Correct answer is: LC filter
Q.12 What does the term ‘efficiency’ refer to in a power supply?
Ratio of output power to input power
Ratio of output voltage to input voltage
Ratio of output current to input current
Ratio of input power to output power
Explanation - Efficiency (η) = (Pout / Pin) × 100% reflects how much input power is converted to useful output power.
Correct answer is: Ratio of output power to input power
Q.13 Which control scheme uses a fixed reference voltage and adjusts duty cycle to regulate output?
Current mode control
Voltage mode control
Pulse‑frequency modulation
Phase‑shift modulation
Explanation - Voltage mode control compares a reference voltage to a feedback voltage and adjusts the duty cycle accordingly.
Correct answer is: Voltage mode control
Q.14 What is the main benefit of using a ‘buck‑boost’ converter?
It can provide output voltage higher or lower than the input
It reduces switching losses
It eliminates the need for a transformer
It improves thermal stability
Explanation - A buck‑boost converter can step up or step down voltage, giving flexibility for varying input conditions.
Correct answer is: It can provide output voltage higher or lower than the input
Q.15 Which parameter of a MOSFET is most critical for switching losses?
Gate charge
Drain‑source on‑resistance
Body diode forward voltage
Threshold voltage
Explanation - The on‑resistance directly contributes to conduction losses during the on‑state of the switch.
Correct answer is: Drain‑source on‑resistance
Q.16 A SMPS operating at 120 kHz typically has:
Very large inductors
Small input capacitors
Long switching rise times
Low EMI
Explanation - Higher switching frequencies allow smaller output/input capacitors, but other components may need to be smaller or higher quality to handle fast transitions.
Correct answer is: Small input capacitors
Q.17 In a flyback converter, the output capacitor is charged during which period?
When the switch is on
When the switch is off
During the dead time
Never – it is always discharged
Explanation - In a flyback, energy is stored in the transformer during the on‑time, then transferred to the output when the switch is turned off.
Correct answer is: When the switch is off
Q.18 The duty cycle (D) of a buck converter is defined as:
Ton / (Ton + Toff)
Toff / (Ton + Toff)
Vin / Vout
Vout / Vin
Explanation - Duty cycle is the ratio of on‑time to total switching period.
Correct answer is: Ton / (Ton + Toff)
Q.19 Which component is typically used to smooth the output of a boost converter?
Inductor
Capacitor
Resistor
Transformer
Explanation - The output capacitor filters the DC component and reduces ripple in the boost converter output.
Correct answer is: Capacitor
Q.20 Which of the following is a key advantage of using a synchronous rectifier?
Simplified circuit design
Reduced conduction losses
Increased output ripple
Lower component count
Explanation - Replacing the diode with a MOSFET reduces forward voltage drop and thus conduction losses.
Correct answer is: Reduced conduction losses
Q.21 What does ‘EMI’ stand for in the context of SMPS?
Electrical Magnetic Interference
Electromagnetic Induction
Electrical Mutual Isolation
Electromotive Inverter
Explanation - EMI refers to unwanted electromagnetic interference produced by high‑frequency switching.
Correct answer is: Electrical Magnetic Interference
Q.22 Which of the following is a common method to increase output voltage ripple in a buck converter?
Increasing the output capacitor
Decreasing the switching frequency
Increasing the duty cycle
Using a larger inductor
Explanation - Lower switching frequencies result in higher ripple because energy is transferred less frequently.
Correct answer is: Decreasing the switching frequency
Q.23 In SMPS, a 'soft‑switching' technique helps to:
Reduce power consumption
Eliminate the need for a transformer
Increase efficiency by reducing switching losses
Simplify the control algorithm
Explanation - Soft‑switching methods like zero‑voltage or zero‑current switching reduce energy lost during transitions.
Correct answer is: Increase efficiency by reducing switching losses
Q.24 Which parameter is directly affected by the choice of MOSFET gate driver voltage?
Switching speed
Drain‑source voltage
Output voltage ripple
Input current draw
Explanation - Higher gate driver voltage charges the MOSFET gate faster, reducing switching transition times.
Correct answer is: Switching speed
Q.25 A typical SMPS can operate at:
Below 50 kHz only
Between 50 kHz and 20 MHz
Only above 20 MHz
Only at 60 Hz
Explanation - SMPS designs cover a wide frequency range; low frequencies are used for high‑power applications, while high frequencies enable smaller components.
Correct answer is: Between 50 kHz and 20 MHz
Q.26 Which of the following is a primary concern in the thermal design of an SMPS?
Capacitor voltage rating
MOSFET package heat dissipation
Switching frequency
Transformer core material
Explanation - MOSFETs generate significant heat; adequate heat sinking is essential to avoid overheating.
Correct answer is: MOSFET package heat dissipation
Q.27 What is the role of a 'snubber' circuit in an SMPS?
To store energy for the next cycle
To protect the MOSFET from voltage spikes
To filter output ripple
To provide isolation
Explanation - Snubber circuits (RC or RCD) dampen voltage transients and prevent damage to the switching device.
Correct answer is: To protect the MOSFET from voltage spikes
Q.28 Which of the following is a disadvantage of high‑frequency switching?
Reduced EMI
Higher conduction losses
Smaller component sizes
Lower output ripple
Explanation - Higher frequencies increase switching losses, though they reduce component size and EMI filtering needs.
Correct answer is: Higher conduction losses
Q.29 In a ‘half‑bridge’ topology, how many switches are required?
One
Two
Four
Eight
Explanation - A half‑bridge uses two switches (MOSFETs or IGBTs) to create a center‑tap voltage source.
Correct answer is: Two
Q.30 What is a common technique to reduce output voltage ripple in a buck converter?
Use a higher duty cycle
Use a lower inductance value
Use a larger output capacitor
Increase the input voltage
Explanation - A larger capacitor smooths the voltage better and reduces ripple amplitude.
Correct answer is: Use a larger output capacitor
Q.31 Which of the following is NOT a typical application of a SMPS?
Computer power supplies
LED drivers
Battery chargers
Incandescent lighting
Explanation - SMPS are used in DC‑DC conversion; incandescent lighting generally uses simple resistive filaments powered directly from mains.
Correct answer is: Incandescent lighting
Q.32 What type of switching device is commonly used in a 100 kHz SMPS for low‑power applications?
IGBT
MOSFET
Thyristor
Silicon Carbide (SiC) diode
Explanation - MOSFETs are efficient, fast‑switching devices ideal for low‑ to medium‑power SMPS.
Correct answer is: MOSFET
Q.33 In which operating region does an inductor maintain a constant current throughout the switching cycle?
Discontinuous Conduction Mode (DCM)
Continuous Conduction Mode (CCM)
Critical Conduction Mode (CCM)
Zero‑Current Switching (ZCS)
Explanation - CCM means the inductor current never falls to zero during the switching period.
Correct answer is: Continuous Conduction Mode (CCM)
Q.34 Which of these parameters is most affected by transformer core saturation?
Output voltage regulation
Switching frequency
Efficiency
Load current capability
Explanation - Core saturation causes loss of flux and affects the transformer’s ability to regulate the output voltage.
Correct answer is: Output voltage regulation
Q.35 What is the main function of a feedback resistor divider in an SMPS?
Set the output voltage reference
Measure the switching frequency
Drive the MOSFET gate
Reduce EMI
Explanation - The resistor divider provides a reference voltage to the feedback amplifier to maintain the desired output voltage.
Correct answer is: Set the output voltage reference
Q.36 In a buck converter, what happens when the input voltage suddenly increases?
Output voltage rises immediately
Duty cycle increases to maintain output
Duty cycle decreases to maintain output
Output voltage remains constant regardless of duty cycle
Explanation - To keep output voltage constant, the control loop reduces duty cycle when input rises.
Correct answer is: Duty cycle decreases to maintain output
Q.37 Which component in an SMPS provides a high‑frequency AC voltage to the transformer?
DC‑DC converter
Power MOSFET
Linear regulator
Battery charger
Explanation - The MOSFET switches the DC input to create a high‑frequency AC waveform that drives the transformer.
Correct answer is: Power MOSFET
Q.38 The output voltage of a buck‑boost converter can be:
Always higher than the input
Always lower than the input
Either higher or lower than the input
Never equal to the input
Explanation - The buck‑boost topology can step up or step down the voltage, depending on duty cycle.
Correct answer is: Either higher or lower than the input
Q.39 Which of the following is an example of a ‘soft‑switching’ technique?
Zero‑Voltage Switching (ZVS)
Full‑Wave Rectification
Full‑Bridge Switching
Hard‑Switching
Explanation - ZVS ensures the switch turns on when voltage across it is zero, reducing switching losses.
Correct answer is: Zero‑Voltage Switching (ZVS)
Q.40 What is the function of the output capacitor in a flyback converter?
Store magnetic energy during switching
Filter the DC output
Reduce input ripple
Provide isolation
Explanation - The capacitor smooths the DC voltage after rectification and energy transfer from the transformer.
Correct answer is: Filter the DC output
Q.41 Which of the following is a common reason for using a ferrite core in the transformer of an SMPS?
To increase the voltage rating
To reduce core losses at high frequency
To improve mechanical strength
To lower the manufacturing cost
Explanation - Ferrite cores have low hysteresis loss, making them ideal for high‑frequency transformers.
Correct answer is: To reduce core losses at high frequency
Q.42 In a DC‑DC converter, the term 'ripple current' refers to:
The variation of input voltage
The variation of output voltage
The variation of current through the inductor
The variation of output current under load changes
Explanation - Ripple current is the AC component of the inductor current superimposed on the DC component.
Correct answer is: The variation of current through the inductor
Q.43 What is the main purpose of an inductor in a buck converter?
To convert AC to DC
To smooth current flow
To regulate voltage
To provide isolation
Explanation - The inductor limits changes in current, providing a steady DC output.
Correct answer is: To smooth current flow
Q.44 Which of the following best describes the duty cycle of a half‑bridge converter when the output voltage is zero?
0%
50%
100%
Cannot be defined
Explanation - If the output is zero, the switch must remain off; thus duty cycle is 0%.
Correct answer is: 0%
Q.45 What type of diode is typically used in a buck converter to achieve low forward voltage drop?
Standard silicon diode
Schottky diode
Zener diode
Light‑emitting diode (LED)
Explanation - Schottky diodes have low forward drop and fast recovery, suitable for high‑speed switching.
Correct answer is: Schottky diode
Q.46 Which of the following is a key advantage of a ‘flyback’ converter compared to a ‘forward’ converter?
Lower cost
Higher efficiency
Smaller size
Higher output power
Explanation - Flyback topologies use a single transformer and can be simpler and cheaper for low‑power applications.
Correct answer is: Lower cost
Q.47 What does the acronym ‘PCB’ stand for?
Printed Circuit Board
Power Circuit Breaker
Pulse‑Control Board
Programmable Current Base
Explanation - PCB is the substrate that hosts all the electrical components in a power supply.
Correct answer is: Printed Circuit Board
Q.48 In an SMPS, the term ‘dead time’ is important to prevent:
Output ripple
Short‑circuit conditions
Shoot‑through of MOSFETs
Voltage spikes on the transformer
Explanation - Dead time ensures the high‑side and low‑side MOSFETs are not on simultaneously, preventing a direct short.
Correct answer is: Shoot‑through of MOSFETs
Q.49 Which of the following components is typically used as an energy storage element in a buck‑boost converter?
Transformer core
Capacitor
Inductor
Resistor
Explanation - The inductor stores magnetic energy and releases it during the off‑phase of the switch.
Correct answer is: Inductor
Q.50 The primary purpose of a ‘snubber’ circuit in a switch‑mode power supply is to:
Prevent over‑voltage on the output
Reduce switching losses
Smooth the DC output
Isolate the load
Explanation - A snubber dampens voltage spikes and reduces dV/dt across the switch, decreasing losses.
Correct answer is: Reduce switching losses
Q.51 Which of the following is a typical operating frequency range for a 48‑V DC‑DC buck converter?
50 Hz – 60 Hz
10 kHz – 100 kHz
200 kHz – 1 MHz
5 MHz – 10 MHz
Explanation - Modern DC‑DC buck converters often operate in the 200 kHz to 1 MHz range to reduce component size.
Correct answer is: 200 kHz – 1 MHz
Q.52 In a flyback converter, what type of core material is commonly used?
Ferrite
Soft iron
Manganese steel
Cobalt‑based alloy
Explanation - Ferrite cores are ideal for high‑frequency transformers due to low core losses.
Correct answer is: Ferrite
Q.53 Which of the following is NOT an advantage of using a ‘synchronous’ rectifier?
Lower conduction losses
Reduced output ripple
Higher switching frequency capability
Higher forward voltage drop
Explanation - Synchronous rectifiers reduce forward voltage drop; they do not increase it.
Correct answer is: Higher forward voltage drop
Q.54 Which of these is a characteristic of an 'output filter' in a power supply?
High resistance
High capacitance
High inductance
Low inductance
Explanation - An output filter uses large capacitors to smooth the DC output and reduce ripple.
Correct answer is: High capacitance
Q.55 What does the abbreviation 'DC‑DC' stand for?
Direct Current – Direct Current
Distributed Circuit – Distributed Current
Dynamic Control – Dynamic Current
Direct Conduction – Dynamic Conduction
Explanation - DC‑DC converters convert one DC voltage level to another.
Correct answer is: Direct Current – Direct Current
Q.56 Which component in a buck converter limits the peak inductor current?
MOSFET drain resistor
Inductor core size
Switching frequency
Output capacitor value
Explanation - The core size determines the saturation current; larger cores allow higher peak currents.
Correct answer is: Inductor core size
Q.57 Which of the following is a direct benefit of increasing the switching frequency of an SMPS?
Higher efficiency
Smaller inductors and capacitors
Lower EMI
Reduced heat dissipation
Explanation - Higher frequency allows smaller magnetic and capacitive components for the same energy transfer.
Correct answer is: Smaller inductors and capacitors
Q.58 The duty cycle of a PWM controller is most often set by:
The input voltage
The output voltage reference
The switching frequency
The MOSFET gate width
Explanation - Duty cycle is adjusted to maintain the desired output voltage set by a reference.
Correct answer is: The output voltage reference
Q.59 Which of the following is a common method to improve EMI performance in an SMPS?
Increase the inductor value
Use a higher voltage transformer
Add a series ferrite bead on the output
Reduce the output capacitor
Explanation - A ferrite bead suppresses high‑frequency noise on the output line.
Correct answer is: Add a series ferrite bead on the output
Q.60 A 'zero‑current switching' (ZCS) technique is beneficial because it:
Eliminates the need for a transformer
Reduces conduction losses to zero
Eliminates switching losses when the switch is off
Simplifies the control loop
Explanation - ZCS ensures the switch turns on when current is zero, minimizing energy lost during turn‑on.
Correct answer is: Eliminates switching losses when the switch is off
Q.61 Which of the following is typically used as a 'soft‑switching' component in an SMPS?
Resistor network
Inductor
Zener diode
Voltage regulator
Explanation - Inductors store energy and enable zero‑voltage or zero‑current switching.
Correct answer is: Inductor
Q.62 In a 'boost' converter, what determines the maximum achievable output voltage?
Maximum duty cycle
Maximum input voltage
Inductor saturation current
Transformer core material
Explanation - The output voltage Vout = Vin / (1 – D); as D approaches 1, Vout increases, limited by the maximum duty cycle.
Correct answer is: Maximum duty cycle
Q.63 Which of the following is NOT a typical reason for a SMPS to be chosen over a linear regulator?
Higher efficiency
Lower heat dissipation
Compact size
High output ripple
Explanation - SMPS can produce low ripple with proper filtering; high ripple is not an advantage.
Correct answer is: High output ripple
Q.64 What type of capacitor is often used at the input of a SMPS to reduce high‑frequency noise?
Electrolytic capacitor
Tantalum capacitor
Ceramic capacitor
Supercapacitor
Explanation - Ceramic capacitors have low ESR and high frequency response, ideal for filtering high‑frequency noise.
Correct answer is: Ceramic capacitor
Q.65 In a ‘half‑bridge’ converter, what is the role of the center tap on the transformer?
To provide isolation
To supply the primary voltage
To divide the secondary voltage
To store energy
Explanation - The center tap provides a reference point and splits the secondary into two equal halves.
Correct answer is: To divide the secondary voltage
Q.66 Which of the following is a major design consideration for the PCB layout of an SMPS?
Wire color coding
Trace width for high currents
Number of layers
Printed labels
Explanation - Adequate trace width is essential to handle the high currents without excessive heating.
Correct answer is: Trace width for high currents
Q.67 A 'half‑bridge' topology is commonly used in which of the following applications?
Laptop chargers
High‑frequency RF amplifiers
High‑power DC‑DC converters
Battery management systems
Explanation - Half‑bridge converters are often used in low‑power, cost‑effective laptop charger designs.
Correct answer is: Laptop chargers
Q.68 What is the primary function of a 'bootstrapping' circuit in a half‑bridge converter?
Provide isolation
Raise the high‑side gate voltage
Reduce EMI
Control duty cycle
Explanation - The bootstrap circuit creates a higher voltage to drive the high‑side MOSFET’s gate.
Correct answer is: Raise the high‑side gate voltage
Q.69 Which of these parameters directly affects the ripple voltage of a buck converter?
Output capacitor ESR
Input voltage
Duty cycle
All of the above
Explanation - Ripple depends on input voltage, duty cycle, and the effective ESR of the output capacitor.
Correct answer is: All of the above
Q.70 What type of switching device is most commonly used in high‑frequency SMPS for power levels above 200 W?
IGBT
MOSFET
GaN MOSFET
SiC MOSFET
Explanation - Silicon Carbide MOSFETs handle high voltage and current with low losses at high frequencies.
Correct answer is: SiC MOSFET
Q.71 Which of the following is the main reason for selecting a 'wide‑bandwidth' feedback loop in an SMPS?
To reduce output voltage ripple
To handle large load transients
To increase switching frequency
To simplify the design
Explanation - A wide‑bandwidth loop responds quickly to load changes, maintaining regulation.
Correct answer is: To handle large load transients
Q.72 In a flyback converter, which component limits the maximum current during the on‑time?
Output capacitor
Flyback transformer core
Inductor of the flyback
MOSFET gate driver
Explanation - The core’s saturation current limits the amount of energy stored during the on‑time.
Correct answer is: Flyback transformer core
Q.73 Which of the following is a typical application of a 'synchronous buck' converter?
Battery chargers
LED drivers
Power amplifiers
Motor drives
Explanation - Synchronous buck converters provide efficient, low‑voltage DC for LED lighting.
Correct answer is: LED drivers
Q.74 What does the term 'over‑current protection' in an SMPS typically involve?
Monitoring output voltage and shutting down
Monitoring output current and shutting down
Monitoring input voltage and shunting it
Monitoring temperature and cooling fans
Explanation - Over‑current protection detects when load current exceeds a threshold and shuts the supply to protect components.
Correct answer is: Monitoring output current and shutting down
Q.75 Which of these is NOT a typical component used for input EMI filtering?
Common‑mode choke
Differential‑mode choke
Ferrite bead
Low‑pass RC filter
Explanation - Low‑pass RC filters are usually for output filtering; input EMI uses chokes and ferrite beads.
Correct answer is: Low‑pass RC filter
Q.76 Which of the following describes 'peak‑to‑peak voltage' in the context of an SMPS output?
The maximum voltage minus the minimum voltage during a cycle
The average voltage of the output
The voltage measured across the load
The difference between input and output voltage
Explanation - Peak‑to‑peak voltage is the range of the voltage ripple waveform.
Correct answer is: The maximum voltage minus the minimum voltage during a cycle
Q.77 Which component in a buck converter provides the energy storage required during the off‑time of the switch?
Diode
Capacitor
Inductor
Resistor
Explanation - During the off‑time, the inductor releases stored energy to the output.
Correct answer is: Inductor
Q.78 In which situation would a ‘flyback’ converter be preferred over a ‘forward’ converter?
High power levels above 1 kW
Low power and cost sensitivity
Need for high isolation voltage
Requirement for continuous current mode
Explanation - Flyback converters are simpler and cheaper for low‑power applications.
Correct answer is: Low power and cost sensitivity
Q.79 Which of the following parameters is most influenced by the switching frequency in a buck converter?
Output voltage ripple
Output current ripple
Inductor size
All of the above
Explanation - Higher switching frequency reduces the required inductor size and decreases both voltage and current ripple.
Correct answer is: All of the above
Q.80 What is the purpose of an 'output voltage feedback' network in a SMPS?
To sense the input voltage
To adjust the duty cycle to maintain output voltage
To detect over‑temperature conditions
To filter EMI on the output
Explanation - The feedback network provides a reference voltage that the control loop uses to keep the output stable.
Correct answer is: To adjust the duty cycle to maintain output voltage
Q.81 Which type of diode is most suitable for high‑speed switching in an SMPS?
Standard silicon diode
Schottky diode
Zener diode
Light‑emitting diode (LED)
Explanation - Schottky diodes have low forward voltage drop and fast recovery, making them ideal for high‑speed switching.
Correct answer is: Schottky diode
Q.82 Which of the following is a key benefit of using a 'synchronous buck' converter instead of a traditional buck converter?
Higher output ripple
Lower conduction losses
Simpler design
Lower efficiency
Explanation - Synchronous buck converters replace the diode with a MOSFET, reducing conduction losses.
Correct answer is: Lower conduction losses
Q.83 In an SMPS, the term 'duty cycle' is:
The ratio of output voltage to input voltage
The percentage of time the switch is on
The maximum current the MOSFET can handle
The amount of ripple voltage
Explanation - Duty cycle = Ton / (Ton + Toff).
Correct answer is: The percentage of time the switch is on
Q.84 Which of the following is a common reason for adding a 'dead‑time' in a half‑bridge SMPS?
To increase efficiency
To prevent shoot‑through
To reduce output ripple
To increase switching frequency
Explanation - Dead‑time ensures that high‑side and low‑side MOSFETs are not on at the same time.
Correct answer is: To prevent shoot‑through
Q.85 Which of the following is a typical component used as a 'flyback transformer' core material?
Ferrite
Soft iron
Manganese steel
Aluminum
Explanation - Ferrite cores are preferred for high‑frequency transformers in flyback SMPS.
Correct answer is: Ferrite
Q.86 In a buck‑boost converter, the output voltage can be expressed as:
Vin * D
Vin / (1 – D)
Vin * (1 – D)
Vin + D
Explanation - The buck‑boost converter equation is Vout = Vin / (1 – D).
Correct answer is: Vin / (1 – D)
Q.87 Which of the following is a typical method to reduce switching losses in high‑frequency SMPS?
Use a larger transformer core
Use a slower MOSFET gate driver
Use a softer‑switching technique
Increase the output capacitance
Explanation - Soft‑switching methods like ZVS or ZCS reduce energy lost during transitions.
Correct answer is: Use a softer‑switching technique
Q.88 Which of the following is NOT a factor influencing the design of the output capacitor in an SMPS?
Output ripple voltage
Output load current
Transformer core material
Capacitor ESR
Explanation - The output capacitor design is influenced by ripple, load, and ESR, not the transformer core.
Correct answer is: Transformer core material
Q.89 Which of the following is a typical application for a 'half‑bridge' SMPS?
USB power banks
Industrial motor drives
Portable phone chargers
Large‑scale power plants
Explanation - Half‑bridge converters are used in low‑cost, low‑power applications such as phone chargers.
Correct answer is: Portable phone chargers
Q.90 Which of the following components provides a low‑impedance path for the inductor current during the off‑time of a buck converter?
Diode
Capacitor
Resistor
Transformer core
Explanation - The diode (or synchronous MOSFET) conducts the inductor current during the off‑time.
Correct answer is: Diode
Q.91 Which of the following is the most common method to measure output voltage in an SMPS?
Use a multimeter on the output
Use a voltage divider and ADC
Use a current transformer
Use an optical sensor
Explanation - A voltage divider scales the output to a safe level for an ADC in the controller.
Correct answer is: Use a voltage divider and ADC
Q.92 In a flyback converter, the output energy is transferred when:
The MOSFET is on
The MOSFET is off
The transformer is saturated
The output capacitor is fully charged
Explanation - During the off‑time, the transformer releases stored energy to the output.
Correct answer is: The MOSFET is off
Q.93 Which of the following is a typical function of the 'controller IC' in an SMPS?
Regulate output voltage
Provide mechanical isolation
Convert AC to DC
Increase input voltage
Explanation - The controller IC monitors the output and adjusts the duty cycle to maintain regulation.
Correct answer is: Regulate output voltage
Q.94 What is the main disadvantage of operating an SMPS at a very high switching frequency?
Increased electromagnetic interference
Higher switching losses
Reduced component size
Lower efficiency at high load currents
Explanation - Higher frequency increases the number of transitions per second, raising switching loss energy.
Correct answer is: Higher switching losses
Q.95 Which component is primarily responsible for the initial storage of energy in a buck‑boost converter?
Transformer core
Inductor
Capacitor
Diode
Explanation - The inductor stores energy during the on‑time and releases it during the off‑time.
Correct answer is: Inductor
Q.96 Which of the following is NOT a typical application of a SMPS?
Battery charger
Motor speed controller
LED driver
Analog audio amplifier (passive)
Explanation - Passive audio amplifiers do not require power conversion; they amplify using AC signals directly.
Correct answer is: Analog audio amplifier (passive)
Q.97 Which of the following is a primary advantage of using a 'synchronous rectifier' in an SMPS?
It reduces EMI
It eliminates the need for a transformer
It reduces conduction losses
It simplifies the control algorithm
Explanation - Replacing the diode with a MOSFET reduces forward voltage drop, lowering conduction losses.
Correct answer is: It reduces conduction losses
Q.98 What is the purpose of a ‘bootstrap capacitor’ in a half‑bridge SMPS?
Provide isolation
Provide high‑side gate voltage
Filter output ripple
Control duty cycle
Explanation - The bootstrap capacitor charges to a voltage higher than input to drive the high‑side MOSFET.
Correct answer is: Provide high‑side gate voltage
Q.99 Which of the following best describes the term 'duty cycle' in a PWM-controlled SMPS?
The ratio of output voltage to input voltage
The ratio of ON time to total switching period
The ratio of output current to input current
The ratio of input frequency to output frequency
Explanation - Duty cycle = Ton / (Ton + Toff).
Correct answer is: The ratio of ON time to total switching period
Q.100 Which of the following is a common design goal for an SMPS to improve EMI performance?
Use larger inductors
Use higher switching frequency
Use a ferrite choke at the input
Use a lower output voltage
Explanation - Ferrite chokes filter high‑frequency noise before it enters the SMPS.
Correct answer is: Use a ferrite choke at the input
Q.101 What is the main role of the ‘output filter’ in a flyback converter?
Store magnetic energy
Smooth the DC output
Provide isolation
Control switching frequency
Explanation - The output filter, typically a capacitor, smooths the DC voltage after rectification.
Correct answer is: Smooth the DC output
Q.102 Which of the following is a typical component used to protect an SMPS against over‑temperature conditions?
Temperature sensor
Current sense resistor
Voltage regulator
Input capacitor
Explanation - A temperature sensor monitors the device’s temperature and can trigger shutdown or fan activation.
Correct answer is: Temperature sensor
Q.103 Which of the following describes the operating principle of a ‘forward’ SMPS converter?
Uses a transformer to step down voltage only
Uses a transformer to step up voltage only
Uses a transformer to transfer energy while maintaining isolation
Does not use a transformer at all
Explanation - The forward converter transfers energy through the transformer while the switch is on, providing isolation.
Correct answer is: Uses a transformer to transfer energy while maintaining isolation
Q.104 Which of the following is a primary characteristic of a ‘zero‑current switching’ (ZCS) SMPS?
Switch turns on when voltage is zero
Switch turns off when current is zero
Switch turns on when current is zero
Switch turns off when voltage is zero
Explanation - ZCS ensures the switch turns on only when the current through it is zero, reducing switching losses.
Correct answer is: Switch turns on when current is zero
Q.105 Which of the following components is used in an SMPS to provide a high‑frequency AC voltage to the transformer?
DC‑DC converter
Power MOSFET
Linear regulator
Transformer primary winding
Explanation - The MOSFET switches the DC input to produce a high‑frequency AC waveform that drives the transformer.
Correct answer is: Power MOSFET
Q.106 What is the primary purpose of a ‘feedback network’ in an SMPS?
To provide isolation
To control output voltage
To reduce ripple
To increase switching frequency
Explanation - The feedback network scales the output voltage and feeds it to the controller for regulation.
Correct answer is: To control output voltage
Q.107 In a ‘buck‑boost’ converter, increasing the duty cycle results in:
Lower output voltage
Higher output voltage
No change to output voltage
Lower output current
Explanation - In a buck‑boost, Vout = Vin / (1 – D); as D increases, Vout increases.
Correct answer is: Higher output voltage
Q.108 Which of the following is a common protection mechanism against reverse polarity of the input supply in an SMPS?
Diode across the input
Transformer isolation
Gate driver
Snubber circuit
Explanation - A diode across the input prevents reverse polarity damage by blocking current when the supply is reversed.
Correct answer is: Diode across the input
Q.109 Which of the following is a typical application for a 'flyback' converter?
Power supply for LED strips
Industrial motor drive
Battery charger
High‑power DC‑DC converter
Explanation - Flyback converters are often used for low‑to‑medium power battery charging circuits.
Correct answer is: Battery charger
Q.110 Which component is typically used to provide the 'high‑side' gate drive voltage in a half‑bridge converter?
Bootstrap capacitor
Pull‑up resistor
Low‑side MOSFET
Transformer primary winding
Explanation - The bootstrap capacitor charges to provide a voltage higher than the input to drive the high‑side MOSFET gate.
Correct answer is: Bootstrap capacitor
Q.111 Which of the following statements about a 'synchronous buck' converter is true?
It uses a diode for rectification
It eliminates the need for a transformer
It uses a MOSFET to replace the diode
It operates only at DC input voltages below 5 V
Explanation - A synchronous buck replaces the diode with a MOSFET, improving efficiency by reducing conduction losses.
Correct answer is: It uses a MOSFET to replace the diode
Q.112 Which of the following is a common source of electromagnetic interference (EMI) in an SMPS?
Switching transients
High input voltage
Large output capacitors
Low output ripple
Explanation - Fast switching transitions produce high‑frequency currents and voltages that radiate as EMI.
Correct answer is: Switching transients
Q.113 In a flyback converter, the 'primary current' is mainly used to:
Store energy in the transformer core
Supply the output directly
Create a magnetic field that is later transferred
Reduce output ripple
Explanation - The primary current generates a magnetic field that stores energy, which is then transferred during the off‑time.
Correct answer is: Create a magnetic field that is later transferred
Q.114 Which of the following is a typical component used as a 'snubber' for a high‑frequency SMPS?
RC snubber
RL snubber
CRL snubber
RLC snubber
Explanation - RC snubbers are common for dampening voltage spikes in high‑frequency SMPS designs.
Correct answer is: RC snubber
Q.115 Which of the following is a key advantage of using a 'flyback' SMPS for low‑power applications?
Higher efficiency
Simpler design
Larger output current
Lower isolation voltage
Explanation - Flyback SMPS requires only one transformer and fewer components, making it simple and cost‑effective for low‑power.
Correct answer is: Simpler design
Q.116 In a buck converter, the output voltage is determined by the duty cycle and the input voltage. Which formula correctly expresses this relationship?
Vout = Vin × D
Vout = Vin / D
Vout = Vin × (1 – D)
Vout = Vin + D
Explanation - In a buck converter, Vout = Vin × D (where D is the duty cycle).
Correct answer is: Vout = Vin × D
Q.117 What is the main function of a 'transformer core' in a flyback converter?
Provide isolation
Store magnetic energy
Reduce EMI
Increase current capacity
Explanation - The transformer core stores energy during the on‑time and releases it during the off‑time.
Correct answer is: Store magnetic energy
Q.118 Which of the following is NOT typically a design consideration for a SMPS input filter?
Capacitor voltage rating
Capacitor ESR
Resonant frequency of the filter
Transformer isolation voltage
Explanation - Isolation voltage is a transformer parameter, not a direct input filter consideration.
Correct answer is: Transformer isolation voltage
Q.119 Which of the following components is used to provide a 'high‑side' gate voltage in a half‑bridge SMPS?
Bootstrap capacitor
Pull‑up resistor
Low‑side MOSFET
Transformer primary winding
Explanation - A bootstrap capacitor charges to a voltage higher than the input to drive the high‑side MOSFET gate.
Correct answer is: Bootstrap capacitor
Q.120 Which of the following is a common feature of 'synchronous rectifier' designs?
Use of a high‑power diode
Use of a MOSFET instead of a diode
Use of a transformer for isolation
Use of a higher input voltage
Explanation - Synchronous rectifiers replace the free‑wheel diode with a MOSFET to reduce conduction losses.
Correct answer is: Use of a MOSFET instead of a diode
Q.121 In a DC‑DC converter, the 'inductor ripple current' is defined as:
The difference between maximum and minimum inductor current
The average current through the inductor
The peak voltage across the inductor
The duty cycle of the converter
Explanation - Ripple current is the AC component of the inductor current, i.e., the variation from its average.
Correct answer is: The difference between maximum and minimum inductor current