DC Choppers and Circuits Quiz
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Questions and Answers

What is the primary function of chopper circuits?

  • To stabilize fluctuating dc voltage
  • To step up fixed ac voltage
  • To convert ac voltage into dc voltage
  • To convert fixed dc voltage into adjustable dc voltage (correct)

    • Which type of chopper circuit is a two-stage conversion process?

  • DC chopper
  • Current Limit Chopper
  • AC Link Chopper (correct)
  • Time Ratio Chopper

    • Which type of control strategy is NOT used in DC choppers?

  • Time Ratio Control
  • Voltage Regulation Control (correct)
  • Current Limit Control
  • Pulse Width Modulation Control

    • Why is dc to dc conversion necessary for household power supply systems?

    <p>Household devices need dc input with adjustable voltage.</p> Signup and view all the answers

    What makes DC choppers more efficient than AC Link Choppers?

    <p>They execute single-stage conversion.</p> Signup and view all the answers

    Which of the following describes a chopper circuit?

    <p>A circuit designed to convert fixed dc voltage into adjustable dc voltage.</p> Signup and view all the answers

    In chopper circuits, what does the term 'static power electronics device' imply?

    <p>It operates without mechanical movement.</p> Signup and view all the answers

    What happens in the DC Chopper circuit?

    <p>It varies the fixed dc input voltage to another level.</p> Signup and view all the answers

    What is a common application needing adjustable dc voltage?

    <p>Electronic devices powered by batteries</p> Signup and view all the answers

    What is the main characteristic of constant frequency operation in time ratio control?

    <p>The ON time is changed while keeping frequency constant.</p> Signup and view all the answers

    Which disadvantage is associated with variable frequency operation?

    <p>It can cause interference with telecommunications.</p> Signup and view all the answers

    What does the current limit control method in a DC-DC converter aim to achieve?

    <p>Keeping the current within upper and lower limits.</p> Signup and view all the answers

    What is a key feature of a voltage-commutated chopper?

    <p>It uses large reverse voltage for thyristor commutation.</p> Signup and view all the answers

    In forced commutation, which elements are primarily used to turn off the thyristor?

    <p>Inductor and capacitor.</p> Signup and view all the answers

    What effect does applying reverse voltage across a conducting thyristor have?

    <p>It reduces the anode current to zero and turns off the thyristor.</p> Signup and view all the answers

    Which commutation technique stops conduction when the load current reaches zero?

    <p>Load Commutation.</p> Signup and view all the answers

    What mechanism allows a chopper to change fixed DC voltage into adjustable DC voltage?

    <p>Duty Cycle Control.</p> Signup and view all the answers

    How is the time ratio control defined in the context of DC-DC converters?

    <p>By changing the duty ratio, K, which is TON/T.</p> Signup and view all the answers

    What is a significant drawback of the frequency modulation technique in DC-DC converters?

    <p>It causes irregular load current due to large OFF times.</p> Signup and view all the answers

    What happens when the main thyristor TM is triggered in the circuit?

    <p>The supply input appears across the load.</p> Signup and view all the answers

    What occurs to the charging current ic between the capacitor voltage equaling the supply input and reaching zero?

    <p>It rises from zero to maximum value.</p> Signup and view all the answers

    Which of the following describes the function of the diode D in the circuit?

    <p>It keeps the voltage across the capacitor constant at –Vs.</p> Signup and view all the answers

    What is the load voltage V0 at instant t2 when the capacitor discharges through the load?

    <p>Vdc + Vdc = 2 Vdc</p> Signup and view all the answers

    What is one characteristic of the step-up chopper?

    <p>It increases the output voltage from the input.</p> Signup and view all the answers

    What happens during the half-cycle when the auxiliary thyristor TA is triggered?

    <p>TM gets reverse biased and becomes non-conducting.</p> Signup and view all the answers

    What assumption is made about the load current in the chopper circuit?

    <p>It is of invariable nature.</p> Signup and view all the answers

    What is indicated by the term 'voltage commutated chopper'?

    <p>The voltage across the capacitor turns off TM.</p> Signup and view all the answers

    In which application are AC choppers typically used?

    <p>For speed control of AC motors.</p> Signup and view all the answers

    What is the role of the thyristor TA during the operation of the chopper?

    <p>It assists in transitioning the current away from load.</p> Signup and view all the answers

    What happens to the charging current once the thyristor TA is triggered?

    <p>It decays to zero.</p> Signup and view all the answers

    What is the load voltage V0 at instant t2 when the capacitor discharges through the load?

    <p>2 Vdc</p> Signup and view all the answers

    What role does the diode D play in the circuit during the charging of the capacitor?

    <p>It keeps the voltage across the capacitor constant.</p> Signup and view all the answers

    What occurs when the capacitor begins to charge again after the thyristor TM is turned off?

    <p>Capacitor charges with reverse polarity.</p> Signup and view all the answers

    What assumption about the load current is made in the chopper circuit?

    <p>It has a constant nature.</p> Signup and view all the answers

    What primarily changes in constant frequency operation to control the output voltage?

    <p>The ON time TON</p> Signup and view all the answers

    What voltage is across the capacitor when the thyristor TM is turned off?

    <p>Vs</p> Signup and view all the answers

    In a step-up chopper, what is primarily manipulated to achieve a higher output voltage?

    <p>Duty cycle.</p> Signup and view all the answers

    What technique uses external components like inductors to turn off a thyristor?

    <p>Current Commutation</p> Signup and view all the answers

    Which of the following describes the disadvantage of using variable frequency operation?

    <p>It may cause load current irregularities</p> Signup and view all the answers

    What happens to the voltage across the capacitor after it gets fully charged?

    <p>It makes the auxiliary thyristor reverse biased.</p> Signup and view all the answers

    What application is a step-down chopper typically used for?

    <p>Power supply voltage reduction.</p> Signup and view all the answers

    In a voltage-commutated chopper, what occurs to initiate the commutation process?

    <p>Large reverse voltage is applied</p> Signup and view all the answers

    What is the maximum value of the commutation current ic when the capacitor voltage equals the supply input?

    <p>It reaches its maximum value.</p> Signup and view all the answers

    What term describes the process of turning off a thyristor in a conducting state?

    <p>Commute</p> Signup and view all the answers

    What allows the load current to freewheel during the OFF state of a DC-DC converter?

    <p>The diode</p> Signup and view all the answers

    Which type of control utilizes duty cycle alterations to change output voltage?

    <p>Time Ratio Control</p> Signup and view all the answers

    What does the term 'duty cycle' refer to in time ratio control?

    <p>The ratio of ON time to total time</p> Signup and view all the answers

    What characteristic makes pulse width modulation preferable over frequency modulation?

    <p>More stable voltage output</p> Signup and view all the answers

    What is the main disadvantage noted for control strategies in DC-DC converters?

    <p>Difficulty in filter design for wide frequency changes</p> Signup and view all the answers

    What is one key function of AC Link Choppers?

    <p>They convert fixed DC into AC, then back to adjustable DC.</p> Signup and view all the answers

    Which statement best describes the operation of a DC Chopper?

    <p>It changes fixed DC input voltage directly to variable DC output.</p> Signup and view all the answers

    What is the primary efficiency advantage of a DC Chopper over an AC Link Chopper?

    <p>It executes direct fixed to variable DC conversion in one stage.</p> Signup and view all the answers

    What is the purpose of Time Ratio Control in DC choppers?

    <p>To change the average output voltage effectively.</p> Signup and view all the answers

    In what scenario would you likely use a chopper circuit?

    <p>To modify the output from a fixed DC voltage source as needed.</p> Signup and view all the answers

    What effect do chopper circuits have on input DC voltage?

    <p>They adjust the fixed DC voltage to a variable level.</p> Signup and view all the answers

    Which of the following accurately describes a characteristic of static power electronics devices like choppers?

    <p>They can change voltage levels without mechanical movement.</p> Signup and view all the answers

    What is the main purpose of converting fixed DC power to adjustable DC power?

    <p>To ensure it fits variable DC voltage device requirements.</p> Signup and view all the answers

    What distinguishes the control strategies of Time Ratio Control and Current Limit Control?

    <p>Only Time Ratio Control adjusts the average output voltage.</p> Signup and view all the answers

    Which of the following statements is true regarding Chopper Circuits and transformers?

    <p>Chopper circuits step up or step down DC voltage like transformers step AC voltage.</p> Signup and view all the answers

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