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Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE) PDF Download

Q16: For the switching converter shown in the following figure, assume steady-state operation. Also assume that the components are ideal, the inductor current is always positive and continuous and switching period is Ts. If the voltage Vis as shown, the duty cycle of the switch S is ______.       (SET-2 (2015))
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)(a) 0
(b) 0.25
(c) 0.5
(d) 0.75
Ans:
(d)
Sol: Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)Hence, it is boost regular,
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
Q17: A buck converter feeding a variable resistive load is shown in the figure. The switching frequency of the switch S is 100 kHz and the duty ratio is 0.6. The output voltage Vo is 36 V. Assume that all the components are ideal, and that the output voltage is ripple-free. The value of R (in Ohm) that will make the inductor current (iL) just continuous is _______.       (SET-2 (2015))
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)(a) 1240
(b) 2500
(c) 3695
(d) 1478
Ans:
(b)
Sol: Condition for boundary of inductor current (iL)
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
Q18: A self commutating switch SW, operated at duty cycle δ is used to control the load voltage as shown in the figure
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)Under steady state operating conditions, the average voltage across the inductor and the capacitor respectively, are      (SET-1 (2015))
(a) Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)

(b) Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
(c) Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
(d) Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
Ans: (a)
Sol: The average voltage across inductor, VL= 0 and hence the given circuit is a boost regular so average voltage across capacitor is equal to average voltage across the load so,
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
Q19: In the following chopper, the duty ratio of switch S is 0.4. If the inductor and capacitor are sufficiently large to ensure continuous inductor current and ripple free capacitor voltage, the charging current (in Ampere) of the 5 V battery, under steady-state, is_____.      (SET-1  (2015)
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)(a) 1
(b) 1.5
(c) 2.5
(d) 3
Ans:
(a)
Sol: Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)Step down chopper
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
Q20: A step-up chopper is used to feed a load at 400 V dc from a 250 V dc source. The inductor current is continuous. If the 'off' time of the switch is 20 μs, the switching frequency of the chopper in kHz is _____.        (SET-2 (2014))
(a) 16
(b) 31.2
(c) 38.25
(d) 45.75
Ans:
(b)
Sol: Given step up chopper,
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
Q21: Figure (i) shows the circuit diagram of a chopper. The switch S in the circuit in figure (i) is switched such that the voltage vD across the diode has the wave shape as shown in figure (ii). The capacitance C is large so that the voltage across it is constant. If switch S and the diode are ideal, the peak to peak ripple (in A) in the inductor current is ______         (SET-1 (2014))
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)(a) 1.5
(b) 2.5
(c) 3.5
(d) 4.5
Ans:
(b)
Sol: The circuit shown is a Buck chopper
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)The peak to peak ripple in the inductor current is
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
Q22: In the figure shown below, the chopper feeds a resistive load from a battery source. MOSFET Q is switched at 250 kHz, with a duty ratio of 0.4. All elements of the circuit are assumed to be ideal.
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)The PEAK-TO-PEAK source current ripple in Amps is      (2013)
(a) 0.96
(b) 0.144
(c) 0.192
(d) 0.288
Ans:
(c)
Sol: Here,
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)∴ ripple source current = (V/L)(D.T.)
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)= 0.192 A

Q23: In the figure shown below, the chopper feeds a resistive load from a battery source. MOSFET Q is switched at 250 kHz, with a duty ratio of 0.4. All elements of the circuit are assumed to be ideal.
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)The average source current in Amps in steady-state is       (2013)
(a) 3/2
(b) 5/3
(c) 5/2
(d) 15/4
Ans
: (b)
Sol: As it is a boost converter, average current through capacitor is zero.
When Q is ON,  I= −I0
Ic = I− I0
Therefore, average through capacitor
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
Q24: In the circuit shown, an ideal switch S is operated at 100 kHz with a duty ratio of 50%. Given that Δic is 1.6 A peak-to-peak and I0 is 5 A dc, the peak current in S is      (2012)
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)(a) 6.6 A
(b) 5.0 A
(c) 5.8 A
(d) 4.2 A
Ans: 
(c)
Sol: Peak current Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)

Q25: In the chopper circuit shown, the main thyristor (TM) is operated at a duty ratio of 0.8 which is much larger the commutation interval. If the maximum allowable reapplied dv/dt on TM is 50 V/μs, what should be the theoretical minimum value of C1 ? Assume current ripple through L0 to be negligible.      (2009)
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)

(a) 0.2 μF
(b) 0.02 μF
(c) 2 μF
(d) 20 μF
Ans:
(a)

Q26: In the circuit shown in the figure, the switch is operated at a duty cycle of 0.5. A large capacitor is connected across the load. The inductor current is assumed to be continuous. The average voltage across the load and the average current through the diode will respectively be      (2008)
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)(a) 10V, 2A
(b) 10V, 8A
(c) 40V, 2A
(d) 40V, 8A
Ans:
(c)
Sol: Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)When, switch is ON, V0 = 0 and i= 0
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)The circuit shown in the figure is step up chopper and for step up chopper, average output voltage,
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)

Average current through diode
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
Q27: A voltage commutated chopper operating at 1 kHz is used to control the speed of dc as shown in figure. The load current is assumed to be constant at 10 A.
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)The average output voltage of the chopper will be      (2006)
(a) 70 V
(b) 47.5 V
(c) 35 V
(d) 0 V
Ans:
(b)
Sol: Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
Q28: A voltage commutated chopper operating at 1 kHz is used to control the speed of dc as shown in figure. The load current is assumed to be constant at 10 A.
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)The minimum time in μ sec for which the SCR M should be ON is      (2006)
(a) 280
(b) 140
(c) 70
(d) 0
Ans: 
(b)
Sol: Initially, main thyristor (m) and auxiliary thyristor (A) are off and capacitor is assumed charged to voltage V with upper plate positive. When 'm' is turned on at t=0, source voltage V is applied across load and load current I0 begins to flow which is assumed to remain constant.
With 'm' ON at t = 0, anotheroscillatory circuit consisting of C, m, L and D is formed where the capacitor current is given by
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)When, ω0t = π, ic = 0
Between
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE) capacitor voltage charges from +Vs to−Vsinusoidally and the lower plate becomes positive.
At ω0t = π, ic = 0, iT1 = I0 and Vc = −Vs
At t1, thyristor A is turned on and capacitor voltage V applies a reverse voltage across thyristor in and SCR 'm' is turned off. The load current is now carried by C and SCR A.
So, minimum time for which SCR 'm' should be ON.
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
Q29: The given figure shows a step-down chopper switched at 1 kHz with a duty ratio D = 0.5. The peak-peak ripple in the load current is close to      (2005)
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)(a) 10A
(b) 0.5A
(c) 0.125A
(d) 0.25A
Ans:
(c)
Sol: Here,
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
Q30: Figure shows a chopper. The device S1 is the main switching device. Sis the auxiliary commutation device. S1 is rated for 400 V, 60 A. S2 is rated for 400 V, 30 A. The load current is 20 A. The main device operates with a duty ratio of 0.5. The peak current through S1 is      (2004)
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)(a) 10A
(b) 20A
(c) 30A
(d) 40A
Ans:
(d)
Sol: Initially main thyristor (S1) and auxiliary thyristor (S2) are off and capacitor is assumed chargeed to voltage Vs with upper plate positive. When S1 is turned on, source voltage Vs is applied across load and load current I0 begins to flow which is assumed to remain constant. With  S1 ON another oscillatory circuit consisting of C,  S1 and L is formed where the capacitor current is given by
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)So current through 𝑆1S1,
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
Q31: Figure shows a chopper operating from a 100 V dc input. The duty ratio of the main switch S is 0.8. The load is sufficiently inductive so that the load current is ripple free. The average current through the diode D under steady state is       (2004)
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)(a) 1.6 A
(b) 6.4 A
(c) 8.0 A
(d) 10.0 A
Ans:
(a)
Sol: Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)During the period TON chopper on and load voltage is equal to source voltage (V= 100V). During the interval TOFF, chopper is off, load current (I0) flows through the diode as result load voltage is zero during TOFF.
Average load voltage,
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)Average load current,
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)As load current is ripple free, so average diode current,
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
Q32: A chopper is employed to charge a battery as shown in figure. The charging current is 5 A. The duty ratio is 0.2. The chopper output voltage is also shown in the figure. The peak to peak ripple current in the charging current is     (2003)
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)(a) 0.48 A
(b) 1.2 A
(c) 2.4 A
(d) 1 A
Ans:
(a)
Sol: Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)During Ton,
Voltage across inductor  
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)Current through inductor,
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)where ΔI = peak to peak ripple current equating A1 and A
A1 = A2
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
Q33: In the chopper circuit shown in figure, the input dc voltage has a constant value Vs. The output voltage Vo is assumed ripple-free. The switch S is operated with a switching time period T and a duty ratio D. what is the value of D at the boundary of continuous and discontinuous conduction of the inductor current iL?      (2002)
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)

(a) D = 1 - (Vs/Vo)
(b) D = 2L/RT
(c) D = 1 - (2L/RT)
(d) D = RT/L
Ans:
(c)
Sol: As the given chopper is buck chopper.
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)this is applicable only at the boundary of continuous and discontinuous
Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)
Q34: A step down chopper is operated in the continuous conduction mode in steady state with a constant duty ratio D. If Vo is the magnitude of the dc output voltage and if Vs is the magnitude of the dc input voltage, the ratio Vo/Vs is given by      (2002)
(a) D
(b) 1-D
(c) 1/(1-D)
(d) D/(1-D)
Ans:
(a)
Sol: Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE)

The document Previous Year Questions- Choppers - 2 | Power Electronics - Electrical Engineering (EE) is a part of the Electrical Engineering (EE) Course Power Electronics.
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FAQs on Previous Year Questions- Choppers - 2 - Power Electronics - Electrical Engineering (EE)

1. What is a chopper in electrical engineering?
Ans. A chopper is a static device that converts fixed DC input voltage to a variable DC output voltage.
2. How does a chopper work?
Ans. A chopper works by turning on and off the semiconductor devices in a specific pattern to regulate the output voltage.
3. What are the applications of choppers?
Ans. Choppers are used in various applications such as speed control of DC motors, voltage regulation, power supplies, and traction systems.
4. What are the types of choppers?
Ans. The main types of choppers are step-up chopper, step-down chopper, and dual-mode chopper.
5. How are choppers different from inverters?
Ans. Choppers are used for DC to DC conversion, while inverters are used for DC to AC conversion. Choppers operate at a fixed frequency, while inverters operate at variable frequencies.
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