Questions and Answers
The class A amplifier is usually biased below cutoff.
False
Darlington pair transistors are often used in power amplifiers because the input impedance is very low.
False
For certain applications with low-resistance loads, a push-pull amplifier using Darlington transistors can be used to decrease the input resistance presented to the driving amplifier and avoid greatly reducing voltage gain.
False
A class B amplifier conducts for ________ of the cycle.
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The class of amplifiers that is the most efficient and has the most distortion is class ________ amplifiers.
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Push-pull amplifiers often use class ________ amplifiers.
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If a class A amplifier has a voltage gain of 50 and a current gain of 75, the power gain is
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If a class A amplifier has RC = 4.7 k and RE = 1.5 k and VCC = 24 V, IC(sat) is
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If an application for an amplifier requires operation in a linear mode, the most likely choice is
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If R1 opened, and Vin at the base was large, Vout at the collector would
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If the diode opened, this amplifier would be operating as
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The purpose of the diode is to bias the amplifier as
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The maximum efficiency for a class A amplifier is about
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The amplifier with the most distortion would be a ________ amplifier.
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With no signal input, the dc emitter voltage with respect to ground is
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This amplifier only shows a positive alternation at the output. The possible trouble might be that
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The dc voltage across RL was measured at 10 V. A possible problem, if any, might be that
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During the positive input alternation, Q1 is ________ and Q2 is ________.
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The purpose for the diodes D1 and D2 is
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The combination of the two transistors is called
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This circuit is operating as a
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An application for a power amplifier to operate at radio frequencies is needed. The most likely choice would be a _________ amplifier.
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The approximate voltages on the base, collector, and emitter, respectively, are
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If RL shows a zero signal voltage on an oscilloscope, the problem might be
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If there were no output signal, and the measured dc voltage of Q1 emitter were 0 V, the trouble might be that
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A class AB amplifier is biased
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Heat sinks reduce the
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An amplifier has two load lines because
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When the Q-point is at the center of the ac load line, a maximum ________ signal can be obtained.
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For maximum peak-to-peak output voltage, the Q-point should be
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The ac load line is the same as the dc load line when the ac collector resistance equals the
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For a Q-point near the center of the dc load line, clipping is more likely to occur on the
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The ac load line usually
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Study Notes
Power Amplifiers Overview
- Class A amplifiers are usually biased above cutoff to provide linear amplification but are only about 25% efficient.
- Class B amplifiers conduct for 180° of the input cycle, optimizing efficiency.
- Class C amplifiers are the most efficient but also the most distorted, suited for applications like RF transmission.
Amplifier Classes
- Class AB amplifiers are biased slightly above cutoff and are commonly used for push-pull configurations to reduce distortion.
- Efficiency of class A amplifiers is limited, with a maximum of around 25%.
- Class C is often used for high-frequency applications due to its efficiency.
Transistor Configurations
- Push-pull arrangements often utilize class B or AB amplifiers to manage load and improve efficiency.
- Darlington pairs are known for high current gain but may not suit all power amplifier requirements due to low input impedance.
Circuit Performance
- Output distortion can occur if particular components fail, such as open resistors or diodes in the circuit.
- The correct biasing is essential to maintain linear operation and optimal performance of the amplifier.
Load Lines and Operating Points
- The ac and dc load lines differ, requiring adjustments for maximum output. The Q-point located at the center of the ac load line produces the highest linear output signal.
- Clipping is more likely to occur at the positive peaks of the output voltage if the Q-point is near the center of the dc load line.
Key Specifications
- Power gain can be calculated as the product of voltage gain and current gain—example: for voltage gain of 50 and current gain of 75, power gain is 3750.
- Maximum voltage output across specified load conditions is essential for designing effective amplifiers.
Component Functions
- Diodes in an amplifier circuit can stabilize biasing against temperature variability.
- Heat sinks are critical to manage the junction temperature in high-power applications, preventing thermal runaway.
Troubleshooting Common Issues
- If output signal is absent or distorted, check for open circuits in critical components (e.g., R1, C3) or malfunctioning transistors.
- Regular measurements across various points in the circuit (emitter, collector, etc.) can help diagnose performance issues effectively.
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Description
This quiz covers the essential concepts of power amplifiers, including classifications like Class A, B, AB, and C. Understand the efficiency and distortion characteristics of each type, along with their applications in real-world scenarios. Test your knowledge of transistor configurations and circuit performance in amplifiers.
