Questions and Answers
What is the efficiency of a class A amplifier?
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?
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What does the output transformer in a single-ended power amplifier have with an AC input signal?
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In the phase splitter circuit, what are the voltage drops across the emitter and collector resistors?
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How are the AC collector and emitter currents in the phase splitter characterized?
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In the phase splitter circuit, which two AC voltages are not in phase?
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Why does the phase splitter operate in the class A mode?
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The phase splitter transistor base voltage is determined by what?
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What is the voltage gain of the phase splitter circuit?
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What is the total signal DC circuit current of a phase splitter?
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What is the relationship between the two output signals of a phase splitter?
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In a typical transistor phase splitter circuit, how are the emitter and collector characterized?
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Why do some push-pull circuits use class AB amplifiers despite class B amplifiers being more efficient?
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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?
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How are the two transistors in a push-pull class AB circuit biased?
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What occurs if the DC bias is removed from a push-pull class AB circuit?
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What is the voltage gain and power gain characteristic in a class AB push-pull amplifier?
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A class AB amplifier conducts for how many degrees of the input signal?
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What is the purpose of the output transformer in a push-pull amplifier?
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A class AB amplifier is more efficient than a class A amplifier.
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Transistors in a class AB push-pull amplifier are slightly forward biased.
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In a complementary amplifier circuit, how are the transistors configured?
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How are the transistors of a complementary amplifier connected?
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In what configuration are the transistors of a complementary amplifier connected?
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How is each transistor of a complementary power amplifier biased?
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What is one advantage of a complementary power amplifier?
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What happens when one of the transistors of the complementary power amplifier is in the active region?
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A class AB transistor conducts for how many degrees of the input signal?
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Complementary power amplifiers have what characteristics?
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What is one purpose of connecting two transistors as a Darlington pair?
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How is a Darlington pair identified?
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In a Darlington pair, what is the relationship between the first-stage emitter current and the second-stage base current?
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In a Darlington pair, how is the current gain calculated?
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The Darlington transistor has high input and very low output impedances.
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The Darlington transistor circuit is used between what types of loads?
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If the two transistors in a Darlington pair are carefully matched to have equal betas, what does the Darlington pair beta equal?
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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!
