📖 Tier 1: Prepare & Study Guide ✓ 100% Solved with Rationales

Power Electronics & Industrial Drives (Electronics Engineering) Solved Questions & Notes (2026) - Apex Rankers

Engineering & Technology > Electronics Engineering > Power Electronics & Industrial Drives

35 Total Solved Questions
~53 mins Estimated Reading Time
1 Subject Areas / Chapters
Select Topic Area / Chapter: Click any section below to switch questions

Power Electronics & Industrial Drives

100%
Showing 25 of 35 (71%)
🎯 Practice
Jump:
Q. 1 Electronics Engineering
Difficulty: Medium (1 Mark)
An SCR (Silicon Controlled Rectifier) can be brought from the conducting state to the blocking state (turned OFF) by:
A
Applying a negative voltage to the gate
B
Reducing the anode current below the holding current
✓ Correct
C
Applying a positive pulse to the cathode
D
Increasing the anode voltage beyond the breakover voltage
💡 Step-by-Step Explanation & Concept Rationale
Once an SCR is turned ON, the gate loses control. The only way to turn it OFF is by natural or forced commutation, which reduces the anode current below the holding current (Ih).
Q. 2 Electronics Engineering
Difficulty: Medium (1 Mark)
What is the primary difference between the latching current and the holding current of a thyristor (SCR)?
A
Latching current is associated with turn-off, holding current with turn-on
B
Latching current is associated with turn-on, holding current with turn-off
✓ Correct
C
Holding current is always greater than latching current
D
Both currents are identical in magnitude and function
💡 Step-by-Step Explanation & Concept Rationale
Latching current is the minimum anode current required to maintain conduction immediately after gate pulse removal (associated with turn-on). Holding current is the minimum anode current below which the device turns OFF (associated with turn-off). Typically, Ilatching ≈ 2 to 3 × Iholding.
Q. 3 Electronics Engineering
Difficulty: Easy (1 Mark)
To protect a thyristor against high rates of rise of voltage (dv/dt), which snubber circuit component is connected across it?
A
An inductor in series with a diode
B
A resistor in series with a capacitor connected in parallel with the SCR
✓ Correct
C
A fuse in series with the anode
D
A zener diode in series with the gate
💡 Step-by-Step Explanation & Concept Rationale
A snubber circuit consisting of a series resistor and capacitor (RC circuit) is connected in parallel with the thyristor to limit dv/dt and suppress transient overvoltages.
Q. 4 Electronics Engineering
Difficulty: Easy (1 Mark)
To protect a thyristor against high rate of rise of current (di/dt) during turn-on, which component is used?
A
A capacitor in parallel with the SCR
B
A small inductor in series with the anode
✓ Correct
C
A metal oxide varistor across the load
D
A fast-recovery diode in antiparallel
💡 Step-by-Step Explanation & Concept Rationale
A small inductor connected in series with the thyristor limits di/dt because an inductor opposes instantaneous changes in current, preventing localized hot spots on the silicon die.
Q. 5 Electronics Engineering
Difficulty: Easy (1 Mark)
A TRIAC is functionally equivalent to which of the following combinations?
A
Two SCRs connected in series
B
Two SCRs connected in inverse-parallel (antiparallel) with a common gate
✓ Correct
C
Two diodes connected in antiparallel
D
An SCR and a BJT in Darlington pair
💡 Step-by-Step Explanation & Concept Rationale
A TRIAC (Triode for Alternating Current) is a bidirectional thyristor equivalent to two SCRs connected in inverse-parallel with gate terminals tied together, allowing conduction in both half-cycles.
Q. 6 Electronics Engineering
Difficulty: Medium (1 Mark)
A DIAC is commonly used in phase-control circuits to:
A
Rectify AC to DC
B
Trigger a TRIAC symmetrically in both positive and negative half cycles
✓ Correct
C
Amplify small audio signals
D
Filter out high-frequency ripple
💡 Step-by-Step Explanation & Concept Rationale
A DIAC (Diode for Alternating Current) is a two-terminal bidirectional breakdown diode used to provide sharp, symmetrical triggering pulses to the gate of a TRIAC.
Q. 7 Electronics Engineering
Difficulty: Easy (1 Mark)
Which power semiconductor device has the characteristics of both a BJT (high current density, low on-state loss) and a MOSFET (high input impedance, voltage-controlled)?
A
GTO (Gate Turn-Off Thyristor)
B
IGBT (Insulated Gate Bipolar Transistor)
✓ Correct
C
TRIAC
D
UJT (Unijunction Transistor)
💡 Step-by-Step Explanation & Concept Rationale
The IGBT combines the insulated gate (voltage-controlled, high input impedance) of a power MOSFET with the bipolar conduction (low saturation voltage drop, high current capability) of a BJT.
Q. 8 Electronics Engineering
Difficulty: Easy (1 Mark)
What is the output voltage of an ideal Step-Down (Buck) DC-DC converter with input voltage Vin and duty cycle D (0 < D < 1) operating in continuous conduction mode?
A
Vout = Vin / (1 - D)
B
Vout = D × Vin
✓ Correct
C
Vout = Vin / D
D
Vout = -D × Vin / (1 - D)
💡 Step-by-Step Explanation & Concept Rationale
In a continuous conduction mode Buck converter, the average output voltage is given by Vout = D × Vin, where D = Ton / T.
Q. 9 Electronics Engineering
Difficulty: Easy (1 Mark)
In a Step-Up (Boost) DC-DC converter with duty cycle D, the ideal relationship between output voltage Vout and input voltage Vin is:
A
Vout = Vin / (1 - D)
✓ Correct
B
Vout = D × Vin
C
Vout = (1 - D) × Vin
D
Vout = D / (1 - D)
💡 Step-by-Step Explanation & Concept Rationale
In a Boost converter, Vout = Vin / (1 - D). Since 0 < D < 1, (1 - D) < 1, making Vout always greater than Vin.
Q. 10 Electronics Engineering
Difficulty: Medium (1 Mark)
A Buck-Boost converter produces an output voltage that is:
A
Always higher than input voltage with same polarity
B
Either higher or lower than input voltage with inverted polarity
✓ Correct
C
Always lower than input voltage with inverted polarity
D
Always equal to input voltage regardless of duty cycle
💡 Step-by-Step Explanation & Concept Rationale
The standard inverting Buck-Boost converter provides Vout = -Vin × (D / (1 - D)). The magnitude can be higher or lower than Vin, and the output polarity is opposite to the input.
Q. 11 Electronics Engineering
Difficulty: Medium (1 Mark)
In a single-phase full-wave controlled bridge rectifier with a resistive load and firing angle alpha, the average DC output voltage is:
A
(Vm / pi) * (1 + cos(alpha))
B
(2 * Vm / pi) * cos(alpha)
✓ Correct
C
(2 * Vm / pi) * (1 + cos(alpha))
D
(Vm / (2 * pi)) * cos(alpha)
💡 Step-by-Step Explanation & Concept Rationale
For a single-phase full converter with continuous conduction, the average DC output voltage is Vdc = (2Vm / pi) * cos(alpha).
Q. 12 Electronics Engineering
Difficulty: Medium (1 Mark)
What is the purpose of connecting a freewheeling diode across an inductive load in a phase-controlled rectifier?
A
To increase the harmonic content of the output
B
To prevent output voltage from going negative and improve load power factor
✓ Correct
C
To step up the DC output voltage
D
To discharge gate trigger capacitors rapidly
💡 Step-by-Step Explanation & Concept Rationale
A freewheeling diode (flyback diode) allows the inductor's stored energy to circulate through the load when source polarity reverses, preventing negative voltage spikes and improving circuit power factor.
Q. 13 Electronics Engineering
Difficulty: Medium (1 Mark)
Which pulse-width modulation (PWM) scheme is most commonly used in three-phase voltage source inverters to reduce low-order harmonic distortion?
A
Single pulse modulation
B
Sinusoidal PWM (SPWM) and Space Vector PWM (SVPWM)
✓ Correct
C
Square wave 120-degree conduction
D
Delta-sigma single-bit modulation
💡 Step-by-Step Explanation & Concept Rationale
Sinusoidal PWM (comparing a sinusoidal reference with a triangular carrier) and Space Vector PWM (SVPWM) are industry standards, shifting harmonic components to high carrier frequencies where they are easily filtered.
Q. 14 Electronics Engineering
Difficulty: Easy (1 Mark)
A Gate Turn-Off (GTO) thyristor differs from a conventional SCR primarily because:
A
It can only conduct in the reverse direction
B
It can be turned OFF by applying a negative current pulse to the gate
✓ Correct
C
It does not require any forward anode voltage to conduct
D
It has three anode terminals and one cathode terminal
💡 Step-by-Step Explanation & Concept Rationale
A GTO can be turned on with a positive gate pulse and turned off by extracting charge with a large negative gate current pulse, unlike standard SCRs which require forced commutation.
Q. 15 Electronics Engineering
Difficulty: Medium (1 Mark)
In a 3-phase inverter operated in 180-degree conduction mode, how many switches are conducting simultaneously at any given instant?
A
Two switches
B
Three switches
✓ Correct
C
Four switches
D
One switch
💡 Step-by-Step Explanation & Concept Rationale
In 180-degree conduction mode, each of the 6 switches conducts for 180 degrees. At any given moment, exactly 3 switches (one from each of the three half-bridges, either 2 top and 1 bottom, or 1 top and 2 bottom) are ON.
Q. 16 Electronics Engineering
Difficulty: Medium (1 Mark)
In a 3-phase inverter operated in 120-degree conduction mode, how many switches conduct at any given instant?
A
One switch
B
Two switches
✓ Correct
C
Three switches
D
Four switches
💡 Step-by-Step Explanation & Concept Rationale
In 120-degree conduction mode, each switch conducts for 120 degrees followed by a 60-degree dead time. Thus, only two switches conduct at any instant, completely preventing shoot-through faults.
Q. 17 Electronics Engineering
Difficulty: Easy (1 Mark)
A cycloconverter is a power electronic circuit that converts:
A
Fixed DC to variable DC
B
Constant AC voltage and frequency to variable AC voltage and lower frequency directly without a DC link
✓ Correct
C
AC to high-voltage DC only
D
Variable DC to 3-phase AC using an intermediate transformer
💡 Step-by-Step Explanation & Concept Rationale
A cycloconverter achieves direct single-stage AC-to-AC frequency conversion without an intermediate DC stage, typically providing output frequencies lower than the input supply frequency.
Q. 18 Electronics Engineering
Difficulty: Medium (1 Mark)
What is the modulation index (m) in Sinusoidal PWM defined as?
A
Ratio of carrier wave frequency to reference sine wave frequency
B
Ratio of peak amplitude of reference sine wave (Vm) to peak amplitude of carrier triangular wave (Vc)
✓ Correct
C
Product of carrier frequency and reference frequency
D
Ratio of DC bus voltage to output RMS voltage
💡 Step-by-Step Explanation & Concept Rationale
Amplitude modulation index ma = Vreference / Vcarrier. When ma <= 1, linear modulation occurs. When ma > 1, overmodulation occurs.
Q. 19 Electronics Engineering
Difficulty: Medium (1 Mark)
In a Unijunction Transistor (UJT) relaxation oscillator, the intrinsic standoff ratio (eta) is given by:
A
RB1 / (RB1 + RB2)
✓ Correct
B
RB2 / (RB1 + RB2)
C
(RB1 + RB2) / RB1
D
RB1 / RB2
💡 Step-by-Step Explanation & Concept Rationale
The intrinsic standoff ratio eta = RB1 / (RB1 + RB2), where RB1 is the base-1 resistance and RB2 is the base-2 resistance of the silicon bar.
Q. 20 Electronics Engineering
Difficulty: Easy (1 Mark)
Which power electronic device has negative resistance region in its I-V characteristic and is commonly used to generate triggering pulses for thyristors?
A
Zener diode
B
UJT (Unijunction Transistor)
✓ Correct
C
Schottky diode
D
BJT in active mode
💡 Step-by-Step Explanation & Concept Rationale
The UJT exhibits a negative dynamic resistance region between peak point (Vp, Ip) and valley point (Vv, Iv), making it ideal for relaxation oscillators to trigger SCRs and TRIACs.
Q. 21 Electronics Engineering
Difficulty: Hard (1 Mark)
What is the function of a Flyback converter transformer in switch-mode power supplies (SMPS)?
A
It acts as a pure step-down transformer transferring energy directly during switch ON time
B
It acts as a coupled inductor, storing energy in its magnetic core during ON time and transferring it to the load during OFF time
✓ Correct
C
It provides power factor correction only
D
It eliminates the need for an output capacitor
💡 Step-by-Step Explanation & Concept Rationale
In a Flyback converter, the 'transformer' is really a coupled inductor with an air gap that stores magnetic energy when the primary switch is ON, and releases it through the secondary diode when the switch turns OFF.
Q. 22 Electronics Engineering
Difficulty: Hard (1 Mark)
In a dual converter operating in circulating current mode, what is the relationship between the firing angles alpha1 and alpha2 of the two converters?
A
alpha1 + alpha2 = 90 degrees
B
alpha1 + alpha2 = 180 degrees
✓ Correct
C
alpha1 - alpha2 = 180 degrees
D
alpha1 * alpha2 = 180 degrees
💡 Step-by-Step Explanation & Concept Rationale
To ensure that average DC voltages of both converters are equal and opposite (Vdc1 + Vdc2 = 0), the firing angles must satisfy alpha1 + alpha2 = 180 degrees.
Q. 23 Electronics Engineering
Difficulty: Hard (1 Mark)
What is the primary advantage of Space Vector PWM (SVPWM) compared to standard Sinusoidal PWM (SPWM)?
A
It increases DC bus voltage utilization by approximately 15.5% and has lower THD
✓ Correct
B
It eliminates the need for microcontroller processing
C
It reduces switching frequency to zero
D
It works without any DC bus capacitor
💡 Step-by-Step Explanation & Concept Rationale
SVPWM utilizes the DC bus voltage up to 2 / sqrt(3) ≈ 1.155 (15.5% higher than sinusoidal PWM) in linear modulation and generates lower harmonic distortion.
Q. 24 Electronics Engineering
Difficulty: Easy (1 Mark)
Which commutation method involves turning off a thyristor by natural reversal of AC supply line voltage?
A
Class A resonant commutation
B
Class F natural (line) commutation
✓ Correct
C
Class C complementary commutation
D
Class D auxiliary impulse commutation
💡 Step-by-Step Explanation & Concept Rationale
Class F commutation, also known as natural or line commutation, occurs when the AC supply voltage naturally alternates to a negative value, driving the thyristor current to zero.
Q. 25 Electronics Engineering
Difficulty: Medium (1 Mark)
What is the role of a commutating capacitor in forced-commutation thyristor circuits?
A
To filter DC ripple across the load
B
To apply a reverse bias voltage across the conducting SCR for a duration greater than its turn-off time (tq)
✓ Correct
C
To increase gate trigger sensitivity
D
To prevent electromagnetic interference in the power grid
💡 Step-by-Step Explanation & Concept Rationale
The commutating capacitor discharges across the conducting thyristor to reverse-bias it for a period greater than its specified turn-off time (toff / tq), sweeping out stored charge carriers.
Study Stream Progress: Showing 25 of 35 Questions (71%)
Jump to:

Ready to Test Your Retention & Speed?

Now that you have reviewed the study questions and rationales, test yourself in our interactive 1-by-1 practice engine or take the full official timed mock exam.