Digital Electronic Systems - DC Power Supply Overview
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Questions and Answers

What is the purpose of the bridge rectifier in the AC rectifier and filter process?

  • To convert high voltage DC into low voltage DC
  • To filter noise from the AC signal
  • To rectify mains AC into high voltage DC (correct)
  • To step down the voltage from the transformer

What component is typically used as a switch in the chopper process?

  • Diode
  • MOSFET (correct)
  • Bipolar Junction Transistor
  • Operational Amplifier

How does increasing the frequency of the switching signal affect the transformer size?

  • It has no effect on the transformer size
  • It makes the transformer less efficient
  • It decreases the transformer size (correct)
  • It increases the transformer size for efficiency

What is the function of the filtering capacitors in the pulsed DC rectifier and filter stage?

<p>To produce non-pulsed DC from stepped down pulsed DC (A)</p> Signup and view all the answers

What is controlled by the duty cycle of the switching signal in a switcher?

<p>The output voltage (B)</p> Signup and view all the answers

What occurs during the positive first quarter-cycle when the capacitor is charging in a half-wave rectifier?

<p>The diode is forward-biased. (B)</p> Signup and view all the answers

What determines the rate at which the capacitor discharges in a half-wave rectifier?

<p>The load resistance and capacitance values. (C)</p> Signup and view all the answers

What is the Peak Inverse Voltage (PIV) in a half-wave rectifier configuration?

<p>2$V_p$ (B)</p> Signup and view all the answers

What is the effect of a larger time constant in the capacitor-input filter?

<p>The capacitor retains its charge longer. (A)</p> Signup and view all the answers

How does the ripple voltage behave in a half-wave rectifier compared to a full-wave rectifier?

<p>It is smaller for a full-wave rectifier. (C)</p> Signup and view all the answers

What is the primary reason a full-wave rectifier is easier to filter than a half-wave rectifier?

<p>It produces a higher output frequency. (A)</p> Signup and view all the answers

What denotes the variation in output voltage due to the charging and discharging of the capacitor?

<p>Ripple voltage. (B)</p> Signup and view all the answers

During which cycle does the diode become reverse-biased in a half-wave rectifier?

<p>When the input voltage drops below capacitor voltage. (B)</p> Signup and view all the answers

What happens to the ripple voltage when the capacitor value increases?

<p>The ripple voltage decreases. (B)</p> Signup and view all the answers

What is the formula for the ripple factor?

<p>r = Vr / VDC * 100% (B)</p> Signup and view all the answers

What is a good guideline for the relationship between load resistance, capacitance, and the period of rectified voltage?

<p>RL C ≥ 10T (D)</p> Signup and view all the answers

What is the primary function of an integrated circuit voltage regulator?

<p>To maintain a constant output voltage. (C)</p> Signup and view all the answers

What is the purpose of combining a capacitor-input filter with an IC regulator?

<p>To produce a low-cost power supply. (D)</p> Signup and view all the answers

Which of the following statements about ripple factor is accurate?

<p>A lower ripple factor implies better filter performance. (B)</p> Signup and view all the answers

Why is it important for the ripple voltage to be less than 10% before entering the regulator?

<p>To ensure accurate voltage regulation. (A)</p> Signup and view all the answers

Which components are typically found in most integrated circuit regulators?

<p>Voltage reference, short-circuit protection, and thermal shutdown circuitry. (B)</p> Signup and view all the answers

What is the primary disadvantage of linear power supplies mentioned?

<p>Large size and weight (C)</p> Signup and view all the answers

Which component is typically used as a switch in the operation of a Switching Mode Power Supply (SMPS)?

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

What happens to transformer size as frequency increases?

<p>Transformer size decreases (C)</p> Signup and view all the answers

How is the output voltage regulated in a Switching Mode Power Supply?

<p>By varying the duty cycle of the switch (C)</p> Signup and view all the answers

Which of the following is NOT an advantage of linear power supplies?

<p>Flexibility in operating voltages (A)</p> Signup and view all the answers

What is the first step in the operation of a Switching Mode Power Supply?

<p>High-voltage AC rectification (D)</p> Signup and view all the answers

What is the function of the transformer in a SMPS?

<p>To convert high frequency pulsed signal to lower voltage (C)</p> Signup and view all the answers

Which supply configuration allows for a reduction in transformer size due to fixed AC mains frequency?

<p>Switching Mode Power Supplies (A)</p> Signup and view all the answers

What is the primary function of a voltage regulator?

<p>To maintain a constant output voltage despite changes in load impedance. (D)</p> Signup and view all the answers

In the context of a voltage regulator, what happens if the output voltage is too high?

<p>The duty cycle of the pulsed gate signal is decreased. (D)</p> Signup and view all the answers

Which type of DC-DC converter increases the input voltage?

<p>Boost converter. (A)</p> Signup and view all the answers

What is one disadvantage of switching mode power supplies (SMPS)?

<p>They are relatively complicated in design. (A)</p> Signup and view all the answers

What role does feedback play in a voltage regulator?

<p>It monitors the output voltage and adjusts the duty cycle accordingly. (B)</p> Signup and view all the answers

Which of the following statements is true regarding SMPS?

<p>They can convert AC to DC and between DC voltages. (B)</p> Signup and view all the answers

What is one way a SMPS can reduce the size of components?

<p>By operating at high frequency to minimize required transformer size. (C)</p> Signup and view all the answers

In an application using a buck-boost converter, what can be expected?

<p>Both an increase and a decrease in output voltage can happen. (A)</p> Signup and view all the answers

What is the minimum peak secondary voltage required for a 7805 regulator to function properly?

<p>9 V (A)</p> Signup and view all the answers

How is line regulation defined?

<p>Change in output voltage for a change in input voltage (C)</p> Signup and view all the answers

What is the formula for calculating load regulation?

<p>(VNL - VFL) / VFL x 100% (C)</p> Signup and view all the answers

For a voltage regulator, why is heat sinking typically necessary?

<p>To prevent overheating of the regulator (B)</p> Signup and view all the answers

If a 7805 regulator has a no-load output voltage of 5.18 V and a full-load output voltage of 5.15 V, what is the load regulation percentage?

<p>0.58% (A)</p> Signup and view all the answers

What does load regulation specifically measure?

<p>Output voltage change over a range of load currents (D)</p> Signup and view all the answers

What is indicated by a high percentage of line regulation?

<p>High stability of output voltage (B)</p> Signup and view all the answers

Which of the following statements is true regarding the use of a transformer with a 7805 regulator?

<p>A transformer with a peak secondary voltage below 9 V is acceptable. (A)</p> Signup and view all the answers

Flashcards

Power Supply

A type of power supply that converts alternating current (AC) into direct current (DC) using diodes and capacitors.

Capacitor-Input Filter

A filter that smooths out the pulsating DC output of a rectifier by using a capacitor to store charge during the positive half-cycle and release it slowly during the negative half-cycle.

Ripple Voltage

The difference between the peak voltage and the minimum voltage in the output of a rectifier after passing through a capacitor-input filter. It's a measure of how much the output voltage fluctuates.

Time Constant

The time it takes for a capacitor to discharge through a load resistance. It's determined by the values of the load resistance (R) and the capacitance (C).

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Peak Inverse Voltage (PIV)

The maximum voltage that the diode in a rectifier can withstand without breaking down. In a capacitor-input filter, the peak inverse voltage (PIV) is twice the peak input voltage.

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Full-Wave Rectifier Output Frequency

The output frequency of a full-wave rectifier is double the output frequency of a half-wave rectifier. This makes full-wave rectification easier to filter.

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Ripple Voltage in Full-Wave and Half-Wave Rectifiers

For a given input frequency and capacitor value, a full-wave rectifier produces a smaller ripple voltage in the output compared to a half-wave rectifier, thanks to its smoother output.

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Ripple Factor

A measure of how effectively a filter reduces ripple voltage in a power supply. Calculated as the ratio of ripple voltage to the DC output voltage, expressed as a percentage.

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T (Period of Rectified Voltage)

The time period of a full-wave rectified voltage waveform, determined by the frequency of the input AC signal.

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RLC >= 10T (Filter Rule of Thumb)

A rule of thumb used to determine the effectiveness of a capacitor-input filter. It suggests that the product of the filter resistance (RL), capacitance (C), and the period of the rectified voltage (T) should be greater than or equal to 10.

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IC Voltage Regulator

A specialized integrated circuit designed for regulating and stabilizing the output voltage of a power supply. It maintains a constant output voltage regardless of input voltage fluctuations, load current changes, or temperature variations.

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Input Terminal (IC Regulator)

The input terminal of an IC voltage regulator connects to the filtered output of the rectifier, typically having a ripple voltage below 10%.

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Output Terminal (IC Regulator)

The output terminal of an IC voltage regulator provides the regulated and stabilized output voltage to the load.

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Reference (Adjust) Terminal

The reference (or adjust) terminal of an IC voltage regulator helps establish the desired output voltage level.

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Line Regulation

A measure of how well a voltage regulator maintains a stable output voltage despite variations in its input voltage. It quantifies the output voltage change for a given input voltage change.

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Load Regulation

A measure of how well a voltage regulator maintains a stable output voltage despite variations in the output current drawn by the load. Quantifies the output voltage change when the load changes from no load to full load.

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Load Regulation Formula

The formula to calculate Load Regulation percentage.

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Minimum Secondary Voltage for 7805 Regulator

The specific voltage required at the secondary winding terminals of the transformer to successfully power a 7805 regulator.

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Heat Sink for 7805

A heat dissipation component used to prevent the 7805 voltage regulator from overheating.

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7805 Voltage Regulator

A type of voltage regulator commonly used in electronic circuits to produce a stable 5 Volt output voltage.

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No Load Output Voltage (VNL)

The output voltage when no load (device) is connected to the regulator.

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Full Load Output Voltage (VFL)

The output voltage of the regulator when the maximum load (device) is connected.

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AC Rectifier

A circuit using diodes to convert alternating current (AC) into direct current (DC).

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Switcher (Chopper)

A device that uses a MOSFET (or other power transistors) to quickly switch high-voltage DC into pulses, often at high frequencies.

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Transformer (SMPS)

A component that steps down high-frequency pulsed DC to a lower voltage, making SMPS smaller and more efficient.

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Pulsed DC Rectifier and Filter

A circuit that further rectifies the pulsed DC output from the transformer, smoothing it into a steady DC voltage.

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SMPS (Switched-Mode Power Supply)

A power supply that uses switching techniques to regulate voltage, typically with high efficiency and smaller size.

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Switching Mode Power Supply (SMPS)

A type of power supply that uses high-frequency switching to convert AC power to DC. They are efficient, compact, and flexible compared to linear power supplies.

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Linear Power Supply

A type of power supply that uses linear circuitry to regulate voltage. They provide clean and reliable output but are bulky and inefficient.

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Rectification

The process of converting alternating current (AC) to direct current (DC).

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Filtering

The process of smoothing out voltage fluctuations, typically by using capacitors.

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Transformer

A device that changes the voltage of an electrical signal.

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MOSFET

A semiconductor device used as a switch in SMPS to chop high-voltage DC into a pulsed signal.

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Duty Cycle

The ratio of 'on' time to the total period of a pulsed signal.

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Voltage Regulator

An electronic circuit that maintains a steady output voltage even when input voltage or load changes.

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Isolated SMPS

A type of SMPS that uses a transformer for electrical isolation and safety.

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Buck Converter

A component that reduces the input voltage of a DC-DC converter.

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Boost Converter

A component that increases the input voltage of a DC-DC converter.

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Buck-Boost Converter

A type of DC-DC converter that can either increase or decrease the input voltage.

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DC-DC Conversion

The process of converting DC voltage to a different DC voltage.

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Study Notes

Digital Electronic Systems (1) - Lecture 1

  • This lecture covers power supplies, specifically the basic DC power supply
  • A DC power supply converts standard 120 V, 60 Hz AC from wall outlets to a constant DC voltage
  • This constant DC voltage powers various electronic circuits, including television receivers, stereo systems, VCRs, computers, and laboratory equipment
  • Power supplies are essential components in electronic systems, ranging from simple to complex circuits
  • A basic power supply comprises a rectifier, a filter, and a regulator
  • The rectifier converts AC input voltage into a pulsating DC voltage (half-wave or full-wave rectified)
  • A capacitor filter smooths out fluctuations in the rectified voltage, producing a relatively stable DC voltage
  • A regulator circuit maintains a constant DC voltage despite variations in input line voltage or load
  • Regulators vary in complexity, from simple components to complex integrated circuits
  • Half-wave rectifiers and full-wave rectifiers are discussed, along with their respective waveforms

Capacitor-Input Filter

  • A half-wave rectifier with a capacitor-input filter is a common circuit configuration
  • During the positive first quarter-cycle of the input, the diode is forward-biased, charging the capacitor
  • The capacitor retains its charge as the input voltage decreases, and the diode becomes reverse-biased
  • The capacitor discharges only through the load resistance, determined by the time constant R₁C
  • The larger the time constant, the less the capacitor discharges
  • The peak inverse voltage (PIV) of the diode in this application is PIV = 2Vp(in)
  • During the next cycle, the diode again becomes forward-biased when the input voltage exceeds the capacitor voltage, recharging the capacitor
  • The variation in the output voltage due to the charging and discharging is known as ripple voltage. Lower ripple is better filtering.
  • For a given input frequency, the output frequency of a full-wave rectifier is twice that of a half-wave rectifier. Therefore, full-wave rectifiers are easier to filter compared to half-wave rectifiers
  • A good rule of thumb for effective filtering is to make R₁C ≥ 10T, where T is the period of the rectified voltage
  • The ripple factor (r) is an indication of filter effectiveness, calculated as r = (Vr/VDC) * 100%

IC Regulated Power Supplies

  • The most effective power supply filter combines a capacitor-input filter with an integrated circuit (IC) voltage regulator
  • The regulator maintains a constant output voltage despite variations in input, load current, and temperature
  • The capacitor-input filter reduces the input ripple to the regulator, enabling stable operation
  • IC regulators are inexpensive, supporting high current output with minimal ripple rejection
  • Three-terminal regulators need only a few external capacitors for a complete power supply, commonly featuring large-value input capacitors and, sometimes, a second, smaller input capacitor for stability
  • Typical output capacitors, around 0.1µF to 1µF, are connected in parallel to improve transient response.
  • Examples of three-terminal regulators include the 78XX series (positive outputs) and 79XX series (negative outputs)
  • The last two digits of the 78XX/79XX number indicate the output voltage
  • For example, a 7812 regulator provides a +12V output and a 7912 provides a -12V output
  • Heat sinking is often required to prevent overheating

Switching Mode Power Supplies (SMPS)

  • Mains AC is rectified and filtered
  • High-voltage DC is pulsed into a high-frequency signal
  • Transformers convert high voltage, high-frequency signal to lower voltage
  • Lower amplitude pulsed DC is filtered into a constant DC output voltage
  • Output voltage regulation is achieved by altering the switching duty cycle of the power switch
  • SMPS offers a significant size and weight advantage over linear power supplies

Percent Regulation

  • Regulation, as a figure of merit, specifies the stability of a voltage regulator in response to input (line) or load changes.
  • Line regulation expresses the percentage change in output voltage for a given input voltage change.
  • Load regulation assesses the impact of load changes on output voltage.

Advantages and Disadvantages of SMPS

  • Advantages: Small size/weight, high efficiency, flexible line voltage/frequency
  • Disadvantages: Complicated design, higher cost, increased conducted and radiated emissions.

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Related Documents

Lecture 1: Digital Electronic Systems (1) PDF

Description

This lecture introduces the fundamentals of DC power supplies, including the conversion of AC to DC voltage. It covers essential components such as rectifiers, filters, and regulators, which ensure stable power for various electronic circuits. Understanding these concepts is crucial for anyone working with electronic systems.

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