Electronics: Capacitors and RC Circuits
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Questions and Answers

A ______ is a circuit component designed to store electrical charge.

capacitor

The time-stationary elements, including the resistor, inductor, and ______, are called passive elements.

capacitor

Capacitance values typically range from picofarads (pF) to ______.

microfarads

When connected to a DC source, a capacitor will charge to the ______ of the source.

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

In RC circuits, pulse response can be used to shape different ______ waveforms.

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

Before the switch is closed, the capacitor is uncharged - plate A and plate B have equal numbers of free ______.

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

When the switch is closed, the source moves electrons away from plate A through the circuit to plate ______.

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

When the capacitor is fully charged, there is no ______.

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

When the charged capacitor is disconnected from the source, it remains charged for long periods of time, depending on its leakage ______.

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

The excess electrons on plate B move through the circuit to plate ______.

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

The current abruptly jumps from 0 to E/R amps, then ______ to zero.

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

Capacitor voltage cannot change instantaneously, that is, it cannot jump abruptly from one value to another. Instead, it climbs gradually and ______.

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

Clippers are networks that employ diodes to 'clip' away a portion of an input signal without distorting the remaining part of the applied ______.

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

The half-wave rectifier is an example of the simplest form of diode ______.

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

In series configuration, the ______ is in series with the load.

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

The diode in a branch parallel to the load represents a ______ configuration.

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

The DC supply can either aid or work against the source ______.

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

For the on condition, the output voltage is given by vo = vi - ______.

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

For the off condition, the output voltage vo equals ______.

<p>0</p> Signup and view all the answers

Diodes will be on for any input voltage vi that is greater than ______ volts.

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

Kirchhoff’s voltage law helps determine the output voltage due to the lack of ______.

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

Since capacitor voltage cannot change instantaneously, its value just after the switch is closed will be the same as it was just before the switch is closed, namely ______ V.

<p>0</p> Signup and view all the answers

An uncharged capacitor looks like a ______ circuit at the instant of switching.

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

Applying Ohm’s law yields iC = E/______ amps.

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

The capacitor is charged to ______ volts prior to switching to position 2.

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

The current thus jumps immediately to –______/R amps.

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

The voltage and current decay to zero from the instant t = ______ s.

<p>0</p> Signup and view all the answers

The voltage and current waveforms are ______.

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

The rate at which a capacitor charges depends on the product of ______ and C.

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

The voltage across a capacitor just after switching is still ______ volts.

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

Flashcards

Capacitor

A circuit component designed to store electrical charge. A capacitor can charge to the voltage of a DC source and hold that charge until it is discharged through a circuit.

Capacitance (C)

The ability of a capacitor to store electrical charge, measured in farads (F).

Capacitor Charging

The process of a capacitor accumulating electrical charge when connected to a DC voltage source.

Capacitor Discharging

The process of a capacitor releasing stored electrical charge when connected to a circuit.

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Time Constant (τ)

The amount of time it takes for a capacitor to charge to approximately 63.2% of the supply voltage or discharge to 36.8% of its initial charge.

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Capacitor Discharge

When a switch is closed, electrons move from the negatively charged plate (plate B) to the positively charged plate (plate A) through the circuit, causing the capacitor to discharge.

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Capacitor Discharge Time

The time it takes for a capacitor to discharge depends on its leakage resistance. Higher leakage resistance means the capacitor retains its charge for a longer duration.

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Energy Dissipation During Discharge

The amount of energy stored in a capacitor is dissipated as heat in the resistance of the circuit during discharge, effectively reducing the voltage across the capacitor.

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Capacitor Voltage During Charging

The capacitor voltage changes gradually and smoothly during charging, rather than jumping abruptly from one value to another. It increases until it reaches the source voltage.

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Capacitor Current During Charging

The current in a circuit with a capacitor initially jumps to a maximum value when the switch is closed, but then exponentially decreases to zero as the capacitor charges.

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Fully Charged Capacitor

The voltage across a capacitor is constant once it reaches the source voltage, meaning there is no current flow, and the capacitor is fully charged.

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Capacitor Voltage Continuity

The capacitor voltage cannot change instantaneously; it gradually increases during charging and decreases during discharging. This behavior is opposite to the sudden jumps in current.

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Diode

A device that allows current to flow in only one direction. It consists of a p-type semiconductor material joined to an n-type semiconductor material.

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Forward voltage drop

The forward voltage drop across a diode, typically around 0.7 volts for silicon diodes.

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Reverse breakdown voltage

The reverse voltage that a diode can withstand before it breaks down and conducts current in the reverse direction.

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Diode Clipper

A type of diode circuit that uses diodes to clip away a portion of an input signal, allowing only a specific part of the signal to pass through.

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Series Clipper

A diode clipper circuit where the diode is connected in series with the load, allowing either the positive or negative portion of the input signal to pass through depending on the diode's orientation.

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Parallel Clipper

A diode clipper circuit where the diode is connected in parallel with the load, allowing either the positive or negative portion of the input signal to pass through depending on the diode's orientation.

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Series Clipper with DC Supply

A diode clipper circuit that utilizes a DC supply in addition to the input signal, allowing for more flexibility in controlling the clipping level.

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On Condition Output

The output voltage across a diode clipper circuit when the diode is conducting current. The output voltage is equal to the input voltage minus the forward voltage drop of the diode.

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Off Condition Output

The output voltage across a diode clipper circuit when the diode is not conducting current. In this case, the output voltage is typically zero volts.

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Capacitor Voltage Change

The voltage across a capacitor cannot change instantly. So, when a switch is closed, the capacitor's voltage remains the same as it was just before the switch was closed.

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Uncharged Capacitor at Switch Closing

At the moment a switch is closed, an uncharged capacitor acts like a short circuit, allowing current to flow through it.

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Capacitor Current at Switch Closing

The current through a capacitor right after a switch is closed is calculated using Ohm's law: iC = E/R amps. This applies since the uncharged capacitor acts like a short circuit.

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Capacitor Current at Steady State

After a capacitor is fully charged, the current through it drops to zero, even though there is still a voltage across the capacitor.

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Capacitor as a Voltage Source during Discharge

In the instant after switching to discharge, the capacitor acts like a voltage source. The initial current is calculated as -E/R amps.

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Capacitor Voltage Waveform during Discharge

The voltage across a capacitor during discharge decreases exponentially over time. The decay starts at the initial voltage and eventually reaches zero.

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Capacitor Time Constant

The time constant (τ) is the time it takes for a capacitor to charge to approximately 63.2% or discharge to 36.8% of its final or initial voltage, respectively. It is determined by the product of R and C (τ = R × C).

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Capacitor Voltage Waveform during Charging

The voltage across a capacitor during charging increases exponentially over time. The increase starts from zero voltage and eventually reaches the full voltage.

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Study Notes

ECT 202 Analog Circuits

  • Course name: Analog Circuits
  • Module number: 1
  • Instructor: Joseph George K N
  • Prerequisites: EST130 Basics of Electrical and Electronics Engineering

Module 1: Wave Shaping Circuits

  • Wave shaping circuits: First order RC differentiating and integrating circuits, First order RC low pass and high pass filters. Diode Clipping circuits - Positive, negative and biased clipper. Diode Clamping circuits - Positive, negative and biased clamper.
  • Transistor biasing: Need, operating point, concept of DC load line, fixed bias, self bias, voltage divider bias, bias stabilization.

Module 2: BJT Amplifiers

  • BJT Amplifiers: RC coupled amplifier (CE configuration). Components needed in design, analysis of CE configuration, concept of AC load lines, voltage gain and frequency response. Small signal analysis using small signal hybrid-pi model for mid frequency and low frequency; analysis of input and output impedance; high frequency equivalent circuits of BJT, Miller effect, high frequency response of CE amplifier.

Module 3: MOSFET Amplifiers

  • MOSFET amplifiers: MOSFET circuits at DC, MOSFET as an amplifier, Biasing of discrete MOSFET amplifier, small signal equivalent circuit; small signal voltage and current gain, input and output impedance of CS configuration; CS stage with current source load, CS stage with diode-connected load, multistage amplifiers, effect of cascading on gain and bandwidth, Cascode amplifier.

Module 4: Feedback Amplifiers and Oscillators

  • Feedback amplifiers: Effect of positive and negative feedback on gain, frequency response and distortion; the four basic feedback topologies; analysis of discrete BJT circuits in voltage-series and voltage-shunt feedback topologies; voltage gain, input and output impedance.
  • Oscillators: Classification, criterion for oscillation, Wien bridge oscillator, Hartley and Crystal oscillator; working principle and design equations of the circuits, analysis of Wien bridge oscillator only required.

Module 5: Power Amplifiers

  • Power amplifiers: Classification, transformer coupled class A power amplifier, push pull class B and class AB power amplifiers; complementary-symmetry class B and Class AB power amplifiers; efficiency and distortion, Analysis not required.

Textbooks and References

  • Textbooks: Robert Boylestad and L Nashelsky, "Electronic Devices and Circuit Theory", 11/e, Pearson, 2015; Sedra A. S. and K. C. Smith, “Microelectronic Circuits”, 6/e, Oxford University Press, 2013.
  • References: Razavi B., “Fundamentals of Microelectronics”, Wiley, 2015; Neamen D., “Electronic Circuits, Analysis and Design”, 3/e, TMH, 2007; David A Bell, “Electronic Devices and Circuits”, Oxford University Press, 2008; Rashid M. H., "Microelectronic Circuits and Design", Analysis and Design, Cengage Learning, 2/e, 2011; Millman J. and C. Halkias, “Integrated Electronics”, 2/e, McGraw-Hill, 2010.

Module 1 Objectives

  • Differentiate between analog and digital circuits.
  • Understand capacitor charging/discharging, voltage and current transients, and time constant.
  • Study pulse response of RC circuits: Differentiator, Integrator, LPF, HPF.
  • Analyze diode clipping, clamping circuits, and predict their output response.
  • Design and analyze different BJT biasing circuits.
  • Perform load-line analysis of common BJT configurations.
  • Study the effect of stability factors of a BJT configuration.

Wave Shaping Circuits

  • Convert one waveform to another
  • Generate sharp narrow pulses/ramp waveforms from sine/rectangular waveforms; RC filters, clipping, clamping circuits.

Capacitor

  • Capacitor function: A circuit component to store electrical charge.
  • Capacitor charging: If connected to a DC source, charges to the source voltage; if disconnected, retains charge until connected to a discharging circuit.
  • Energy stored: E = 1/2 * C * V2
  • Capacitor value ranges: from picofarads (pF) to microfarads (µF). The higher the capacitance, the more charge it can hold for a given voltage.
  • Capacitor use: For signal conditioning and timing.
  • Capacitor current and voltage during charging: The current abruptly jumps to E/R amps and then decays to zero whereas the voltage gradually increases to E volts.
  • Capacitor behavior in dc circuits: A capacitor acts as a short circuit to instantaneous changes in voltage and an open circuit to constant voltage.
  • Capacitor charging/discharging equations and waveforms: exponential.

Time constant

  • The rate of capacitor charging depends on the product of R and C, called the time constant, symbolized by τ and given by: τ = RC (seconds).
  • Units: seconds; resistance in ohms and capacitance in farads is used to calculate tau.
  • Duration of a transient is typically about 5 time constants.

RC Filters

  • Frequency selective circuits (Low, high, band-pass, band-reject.)
  • Response (gain) varies based on frequency. A certain frequency range is passed while others are blocked.

Diode Clipping Circuits

  • Diode clipping circuits: Networks that use diodes to cut/remove a portion of an input signal without affecting the remainder of the waveform.

  • Types of clipping circuits: Series and parallel.

  • For a series clipper, the diode is in series with the load. For a parallel configuration, the diode is in parallel with the load.

  • Ideal diodes: A diode in the on state is a short circuit and an open circuit when it is off.

  • Non-ideal diodes (considering the diode voltage drop): In on state the diode acts as voltage source V and is replaced by a short circuit model, whereas in off state it is replaced by an open-circuit model.

  • Concepts of transfer characteristics, transition voltage.

  • Zener diodes: Diodes that conduct in the reverse direction at a specific voltage (zener voltage), with current regulated. The transfer characteristic represents the voltage and current relation of the device.

Transistor Biasing

  • Transistor biasing details: DC load line, fixed bias, self bias, voltage divider bias, bias stabilization are discussed.

Diode Clamping Circuits

  • Basic diode clamping circuits: Diode, resistor, capacitor and a dc supply are used.
  • The resistor and capacitor must be selected to have a large time constant so that the capacitor retains its voltage during the period the diode is non-conducting.
  • Analyzed by noting that the capacitor charges instantaneously to Vo with either -V or +V polarity during non-conducting periods in the circuit, and assuming that the capacitor charges/discharges within five time constants.

Transfer Characteristics

  • Plotting Vo vs Vi, plotting of voltage waveforms for input and output.

  • The information presented details the materials and topics in the provided documents.

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Test your knowledge on capacitors and their role in RC circuits with this quiz. Learn about the properties, functions, and behaviors of capacitors in electrical circuits. Challenge yourself with questions on charging, response, and current flow.

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