Transistor Power Amplifiers Quiz
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Questions and Answers

What is the efficiency of a class A amplifier?

  • Most efficient
  • Moderately efficient
  • Infinitely efficient
  • Least efficient (correct)

    • In a class A power amplifier, what does the total circuit current with an AC input signal equal?

    Total circuit current with no AC input signal

    Why might a transformer be used in a power amplifier?

    To match the load impedance to the transistor output impedance

    What is the collector DC voltage in a single-ended power amplifier?

    <p>Almost equal to the supply voltage</p> Signup and view all the answers

    What does the output transformer in a single-ended power amplifier have with an AC input signal?

    <p>AC and DC current in the primary coil</p> Signup and view all the answers

    In the phase splitter circuit, what are the voltage drops across the emitter and collector resistors?

    <p>Essentially equal</p> Signup and view all the answers

    How are the AC collector and emitter currents in the phase splitter characterized?

    <p>In phase and about equal</p> Signup and view all the answers

    In the phase splitter circuit, which two AC voltages are not in phase?

    <p>The emitter and the collector</p> Signup and view all the answers

    Why does the phase splitter operate in the class A mode?

    <p>Total DC circuit current is unaffected by AC current</p> Signup and view all the answers

    The phase splitter transistor base voltage is determined by what?

    <p>Values of the voltage divider resistors at the base</p> Signup and view all the answers

    What is the voltage gain of the phase splitter circuit?

    <p>Slightly less than 1.0</p> Signup and view all the answers

    What is the total signal DC circuit current of a phase splitter?

    <p>Equal to the no-signal total DC circuit current</p> Signup and view all the answers

    What is the relationship between the two output signals of a phase splitter?

    <p>180 degrees out of phase</p> Signup and view all the answers

    In a typical transistor phase splitter circuit, how are the emitter and collector characterized?

    <p>All of the above</p> Signup and view all the answers

    Why do some push-pull circuits use class AB amplifiers despite class B amplifiers being more efficient?

    <p>Two class B amplifiers can cause crossover distortion</p> Signup and view all the answers

    If the AC input signal is 0 for the class AB push-pull circuit, what happens to the AC base currents of Q1 and Q2?

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

    How are the two transistors in a push-pull class AB circuit biased?

    <p>Both biased near cutoff</p> Signup and view all the answers

    What occurs if the DC bias is removed from a push-pull class AB circuit?

    <p>Crossover distortion of the AC output occurs</p> Signup and view all the answers

    What is the voltage gain and power gain characteristic in a class AB push-pull amplifier?

    <p>Voltage gain is low and power gain is high</p> Signup and view all the answers

    A class AB amplifier conducts for how many degrees of the input signal?

    <p>Between 180 and 360 degrees</p> Signup and view all the answers

    What is the purpose of the output transformer in a push-pull amplifier?

    <p>All of the above</p> Signup and view all the answers

    A class AB amplifier is more efficient than a class A amplifier.

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

    Transistors in a class AB push-pull amplifier are slightly forward biased.

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

    In a complementary amplifier circuit, how are the transistors configured?

    <p>One must be a PNP and the other must be an NPN</p> Signup and view all the answers

    How are the transistors of a complementary amplifier connected?

    <p>In series</p> Signup and view all the answers

    In what configuration are the transistors of a complementary amplifier connected?

    <p>Common collector configurations</p> Signup and view all the answers

    How is each transistor of a complementary power amplifier biased?

    <p>Near the cutoff point</p> Signup and view all the answers

    What is one advantage of a complementary power amplifier?

    <p>No need for an input phase splitter transformer</p> Signup and view all the answers

    What happens when one of the transistors of the complementary power amplifier is in the active region?

    <p>The other transistor is, for most of the half cycle, at cutoff</p> Signup and view all the answers

    A class AB transistor conducts for how many degrees of the input signal?

    <p>More than 180 but less than 360 degrees</p> Signup and view all the answers

    Complementary power amplifiers have what characteristics?

    <p>High input impedance, low output impedance, high current gain, and low voltage gain</p> Signup and view all the answers

    What is one purpose of connecting two transistors as a Darlington pair?

    <p>To have a very large current gain</p> Signup and view all the answers

    How is a Darlington pair identified?

    <p>By the direct connection between the first-stage emitter and the second-stage base</p> Signup and view all the answers

    In a Darlington pair, what is the relationship between the first-stage emitter current and the second-stage base current?

    <p>Emitter current equals the second-stage base current</p> Signup and view all the answers

    In a Darlington pair, how is the current gain calculated?

    <p>Second-stage collector current divided by the first-stage base current</p> Signup and view all the answers

    The Darlington transistor has high input and very low output impedances.

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

    The Darlington transistor circuit is used between what types of loads?

    <p>High impedance source and low impedance load</p> Signup and view all the answers

    If the two transistors in a Darlington pair are carefully matched to have equal betas, what does the Darlington pair beta equal?

    <p>The square of the transistor beta</p> Signup and view all the answers

    Study Notes

    Class A Amplifiers

    • Class A amplifiers have the lowest efficiency but produce the least distortion.
    • AC input signals do not affect total circuit current; it remains the same as DC.

    Transformer Use in Amplifiers

    • Transformers couple the load to the collector circuit to match load impedance with transistor output impedance.

    Single-Ended Power Amplifiers

    • In single-ended power amplifiers, collector DC voltage nearly matches the supply voltage.
    • The output transformer carries both AC and DC current in the primary coil.

    Phase Splitter Circuits

    • The voltage drop across emitter and collector resistors in a phase splitter is nearly equal.
    • AC collector and emitter currents are in phase and approximately equal.
    • Emitter and collector AC voltages are not in phase, differing by 180 degrees.

    Phase Splitter Characteristics

    • Phase splitter operates in class A, where total DC circuit current remains unaffected by AC current.
    • Base voltage of the phase splitter transistor is determined by the voltage divider resistors.
    • Capacitors at input and outputs isolate DC bias voltages from AC signals.

    Signal Characteristics in Phase Splitters

    • Phase splitter voltage gain is slightly less than 1.0.
    • Total signal DC circuit current matches no-signal total DC current.
    • Two output signals from a phase splitter are 180 degrees out of phase.
    • Emitter and collector resistances, currents, and circuit voltage drops are equal in a typical phase splitter.

    Class AB Amplifiers

    • Class B amplifiers are less power-dissipating than class AB; class AB counters crossover distortion in push-pull circuits.
    • When AC input is zero, AC base currents of transistors Q1 and Q2 in class AB push-pull are also zero.
    • Transistors in a push-pull class AB circuit are biased near cutoff.
    • Removal of DC bias from push-pull class AB circuits leads to crossover distortion.

    Performance and Characteristics

    • Class AB amplifiers exhibit low voltage gain but high power gain.
    • They conduct for an input signal range between 180 and 360 degrees.
    • The output transformer combines two collector signals into one, matches low impedance loads, and provides a DC path for supply voltage.
    • Class AB amplifiers are more efficient than class A amplifiers and operate with slightly forward biased transistors.

    Complementary Amplifier Circuits

    • A complementary amplifier consists of a PNP and NPN transistor.
    • Transistors are connected in series configuration, typically in common collector arrangements to reduce distortion.
    • Biasing near cutoff minimizes power consumption and nullifies the need for a phase splitter transformer.

    Darlington Pair Transistors

    • Complementary power amplifiers have high input impedance, low output impedance, high current gain, and low voltage gain.
    • Darlington pairs aim for significant current gain, with the first-stage emitter connected directly to the second-stage base.
    • In a Darlington pair, first-stage emitter current equals second-stage base current.
    • Current gain in a Darlington pair is achieved by dividing second-stage collector current by first-stage base current.
    • Darlington transistors possess very high input impedance and low output impedance, suitable for high impedance sources feeding low impedance loads.
    • When two transistors in a Darlington pair have matching beta values, the overall beta equals the square of an individual transistor's beta.

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    Description

    Test your knowledge on transistor power amplifiers, specifically focusing on class A amplifiers. This quiz covers key definitions and concepts essential for understanding their operation and characteristics. Perfect for students or enthusiasts in electronics!

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