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Test: Step Up Choppers - Electrical Engineering (EE) MCQ


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10 Questions MCQ Test Power Electronics - Test: Step Up Choppers

Test: Step Up Choppers for Electrical Engineering (EE) 2024 is part of Power Electronics preparation. The Test: Step Up Choppers questions and answers have been prepared according to the Electrical Engineering (EE) exam syllabus.The Test: Step Up Choppers MCQs are made for Electrical Engineering (EE) 2024 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Test: Step Up Choppers below.
Solutions of Test: Step Up Choppers questions in English are available as part of our Power Electronics for Electrical Engineering (EE) & Test: Step Up Choppers solutions in Hindi for Power Electronics course. Download more important topics, notes, lectures and mock test series for Electrical Engineering (EE) Exam by signing up for free. Attempt Test: Step Up Choppers | 10 questions in 30 minutes | Mock test for Electrical Engineering (EE) preparation | Free important questions MCQ to study Power Electronics for Electrical Engineering (EE) Exam | Download free PDF with solutions
Test: Step Up Choppers - Question 1

A step-up chopper is used to deliver a load voltage of 500 V from a 220 V d.c. source. If the blocking period of the thyristor is 80 μs, the required pulse width is -

Detailed Solution for Test: Step Up Choppers - Question 1

Concept:

The output voltage of a step-up chopper is given by:

where, Vo = Output voltage 

Vin = Input voltage

D = Duty cycle

The duty cycle is given by:

TON is the pulse width of the output.

Calculation:

Given, Vo = 500 V

Vin = 220 V

Toff = 80 μs

Test: Step Up Choppers - Question 2

A self-commutating switch SW, operated at duty cycle δ is used to control the load voltage as shown in the figure.

Under steady state operating conditions, the average voltage across the inductor and the capacitor respectively, are

Detailed Solution for Test: Step Up Choppers - Question 2

Identification of DC-DC Converter:

  • Buck converter: Inductor is connected in series with the combination of the capacitor and resistor.
  • Boost converter: Inductor is connected in series with the supply voltage source.
  • Buck-Boost converter: Inductor is connected in parallel to the supply voltage source.

Under steady-state operating conditions:

  • The average voltage across the inductor is zero. VL = 0
  • The average current across the capacitor is zero. IC = 0

Given DC-DC converter is a Boost converter with duty cycle ratio δ.

The voltage across the load is the same as the voltage across the capacitor.

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Test: Step Up Choppers - Question 3

The input voltage VDC of the buck-boost converter shown below varies from 32 V to 72 V. Assume that all components are ideal, inductor current is continuous, and output voltage is ripple free. The range of duty ratio D of the converter for which the magnitude of the steady-state output voltage remains constant at 48 V is

Detailed Solution for Test: Step Up Choppers - Question 3

Concept:

For a buck-boost converter,

Calculation:

Given that,

Source voltage (VDC) = 32 V to 72 V

Output voltage, (V0) = 48 V

For a buck-boost converter,

Where D is duty ratio

When VDC = 32V,

Test: Step Up Choppers - Question 4

If the duty ratio of a boost converter is 50 percent, the output voltage corresponding to an input of 25 V is

Detailed Solution for Test: Step Up Choppers - Question 4

Concept:

The circuit diagram of a boost converter is shown below.

Step Up or Boost converter is used to obtain the output voltage greater than the input voltage.

The relation between the output voltage and the input voltage is given by

Where D is the duty cycle of the chopper

Calculation:

Duty ratio = 50 % = 0.5

Input voltage (VS) = 25 V

Average output voltage (Vo) =

Test: Step Up Choppers - Question 5

A step-up chopper is fed with 200 V. The conduction time of the thyristor is 200 µs and the required output is 600 V. If the frequency of operation is kept constant and the pulse width is halved, what will be the new output voltage?

Detailed Solution for Test: Step Up Choppers - Question 5

Formula:

Where, Vo is the output voltage

Vin is the input voltage

TON is the pulse width

Application:

Given,

Vin = 200 volts

TON = 200 µs

V0 = 600 V

From equation (1),

or, 3T - 600 = T

Hence, T = 300 µs

If the Pulse width is half then, the new value of pulse width (TON') will be,

Hence,

Hence, the new value of output voltage (V0') will be,

Test: Step Up Choppers - Question 6

Consider the boost converter of the input voltage to this converter is 6 V. The average output voltage is Vo = 18 V and the average load current Io = 0.4 A. If the switching frequency is 20 kHz for L = 250 μH, then the ripple current of inductor is _______A.

Detailed Solution for Test: Step Up Choppers - Question 6

Concept:

When the switch is ON:

Applying KVL as per loop:

Calculation:

Test: Step Up Choppers - Question 7

A step-up dc chopper has input dc voltage of 200 V and average output voltage 500 V. If the conduction time of the switch is 150 μs, determine the pulse width of the output voltage.

Detailed Solution for Test: Step Up Choppers - Question 7

Concept: 

The output voltage of a step-up chopper is given by:

where,

Vo = Output voltage

VS = Input voltage

D = Duty cycle

The duty cycle (D) is

where,

TON = Conducting period or pulse width in seconds

TOFF = Non-conducting period in seconds.

T = Total conducting period = Pulse width.

T = TON + TOFF

Calculation:

Given

 TON =150 μs

Vo =  500 V

VS = 200 V

T = 250 μs

Test: Step Up Choppers - Question 8

The minimum inductance (Lmin) for continuous current for a boost converter is given by (where D is duty ratio):

Detailed Solution for Test: Step Up Choppers - Question 8

Concept

At the edge of the continuous conduction, the value of inductance becomes minimum and such value of inductance is known as the critical inductance of the converter.

At the boundary of continuous conduction, IL(min) = 0

Calculation of ΔIL

When the switch is ON:

Putting this value in equation (i):

The value of the minimum inductance (Lmin) for continuous current for a boost converter is given by:

Test: Step Up Choppers - Question 9

A step up chopper delivers an average output voltage of 100 V from an input supply of 60 V when operating with a continuous source current. What is the operating duty ratio for the switch?

Detailed Solution for Test: Step Up Choppers - Question 9

Concept:

The circuit diagram of a boost converter is shown below.

A step-up or Boost converter is used to obtain the output voltage greater than the input voltage.

The relation between the output voltage and the input voltage is given by

Where D is the duty cycle of the chopper

Calculation:

Input voltage (VS) = 100 V

Average output voltage (Vo) = 60 V

*Answer can only contain numeric values
Test: Step Up Choppers - Question 10

Figure (i) shows the circuit diagram of a chopper. The switch s in the circuit in the figure (i) is switched such that the voltage VD across the diode has the waveshape as shown in the figure (ii). The capacitance C is large so that the voltage across it is constant. If the switch s and diode d are ideal

The peak to peak ripple (in A) in the inductor current is-


Detailed Solution for Test: Step Up Choppers - Question 10

Concept:

The circuit diagram of the buck converter is shown below.

The waveforms of current flows through the resistor, inductor, and capacitor are shown below.

The waveforms of ripple current and voltage are shown below.

Calculation:

For buck converter, peak to peak ripple current is given by,

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