EE 318 Chapter 5: DC to DC Converter (Chopper)

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Questions and Answers

What is the output voltage of the circuit in the first equation?

  • 30 V
  • 40 V
  • 20 V (correct)
  • 10 V

What is the value of I/01 in the given equation?

  • 1.25 A
  • 2.25 A
  • 2.75 A
  • 1.75 A (correct)

What is the design requirement for the output voltage ripple in Example 5.3?

  • 2 percent
  • 0.1 percent
  • 0.5 percent (correct)
  • 1 percent

What is the duty ratio of the buck converter in Example 5.3?

<p>0.375 (B)</p> Signup and view all the answers

What is the switching frequency assumed in Example 5.3?

<p>40 kHz (A)</p> Signup and view all the answers

What is the minimum inductor size determined from in Example 5.3?

<p>78 μH (B)</p> Signup and view all the answers

What is the value of the inductor chosen in Example 5.3?

<p>97.5 μH (C)</p> Signup and view all the answers

What is the input voltage of the buck converter in Example 5.3?

<p>48 V (D)</p> Signup and view all the answers

What is the load resistance of the buck converter in Example 5.3?

<p>10 Ω (C)</p> Signup and view all the answers

What is the required output voltage of the buck converter in Example 5.3?

<p>18 V (A)</p> Signup and view all the answers

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Study Notes

DC-DC Converter (Chopper)

  • A DC-DC converter is a power electronic circuit that converts a DC voltage to a different DC voltage level, often providing a regulated output.
  • Applications include switched-mode power supply (SMPS), DC motor control, and battery chargers.

Main Types of Choppers

  • Step-down DC-DC converter: output voltage is less than input voltage.
  • Step-up DC-DC converter: output voltage is more than input voltage.
  • Buck-Boost converter (Step-down/step-up converter): output voltage can be more or less than input voltage.

DC Chopper with Resistive Load

  • A DC chopper with a resistive load consists of a DC input voltage source, a controllable switch, and a load resistance.
  • The switch is operated with a duty ratio (D) defined as the ratio of the switch ON time to the sum of the ON and OFF times.
  • Chopping period (T) = TON (ON time) + TOFF (OFF time).
  • Chopping frequency (F) = 1/T.

Buck (Step-Down) Converter

  • The input voltage is connected to a controllable semiconductor device that operates as a switch.
  • The switch rapidly turns on and off, controlling the flow of current through the circuit.
  • A diode is used to allow current to flow when the switch is off, providing a path for the inductor's energy to discharge.

Principle of Operation

  • When the switch is turned on, the input voltage is connected to the inductor, causing the current to increase.
  • When the switch is turned off, the inductor releases its energy, and the diode becomes forward-biased.

Steady-State Operation

  • The net change in current through the inductor in one complete cycle is zero.
  • The average inductor current must be the same as the average current in the load resistor.

Output Voltage Ripple

  • The variation in output voltage, or ripple, is computed from the voltage-current relationship of the capacitor.
  • The ripple factor can be reduced by increasing the switching frequency, inductor size, or capacitor size.

Continuous Current Mode (CCM) Operation

  • Imin = 0 is the boundary between continuous and discontinuous current.
  • To ensure continuous current, Imin ≥ 0, and L ≥ Lmin.

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