Transistor Amplifiers - Class A, AB, B, & C Circuits | Summary and Q&A

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April 13, 2020
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The Organic Chemistry Tutor
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Transistor Amplifiers - Class A, AB, B, & C Circuits

TL;DR

This video discusses different types of transistor amplifiers, including class A, class AB, class B, and class C, and the differences in their efficiency and distortion.

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Questions & Answers

Q: What is the key difference between a class A and class B amplifier?

The key difference is that a class A amplifier conducts for the entire input cycle, while a class B amplifier conducts for only half of the input cycle. This results in higher efficiency for the class B amplifier but with the tradeoff of crossover distortion.

Q: How can the efficiency of a class A amplifier be increased?

One way to increase the efficiency of a class A amplifier is by replacing the collector resistor with a transformer. The transformer can absorb and release stored energy using its magnetic fields, increasing the overall efficiency of the circuit.

Q: What is the advantage of using a class AB amplifier over a class B amplifier?

The class AB amplifier reduces crossover distortion, which is present in class B amplifiers, by replacing a resistor with two silicon diodes. This improves the overall performance of the amplifier.

Q: Why does the class C amplifier have high distortion?

The class C amplifier conducts for less than 180 degrees of the input cycle, resulting in severe distortion. This is due to its tuned circuit design and the non-linear characteristics of the transistor.

Summary & Key Takeaways

  • The class A amplifier, also known as the common emitter amplifier, has low efficiency but little to no distortion. It is used as a small signal amplifier rather than a power amplifier.

  • The class B amplifier uses complementary transistors and conducts for only one half of the input cycle. It has higher efficiency but suffers from crossover distortion.

  • The class AB amplifier is an improvement of the class B amplifier that uses diodes to reduce crossover distortion.

  • The class C amplifier is a tuned amplifier using a single transistor and exhibits high efficiency but severe distortion.

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