Bipolar transistors

Which value is closest to the maximum power efficiency of an ideal class B push-pull amplifier?

  1. AAbout 100%
  2. BAbout 78.5%
  3. CAbout 25%
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Answer: B. About 78.5%

In class B amplification, each of the two transistors operates for half of the cycle, and almost no current flows when there is no signal. The ideal maximum efficiency is π/4 ≈ 78.5%, higher than class A, which always carries bias current (maximum 25% with a resistive load).

  • A. Voltage drops across the transistors mean linear amplification cannot reach 100%.
  • B. Correct. The theoretical maximum efficiency is π/4 ≈ 78.5%.
  • C. About 25% is the maximum efficiency of a class A amplifier with a resistive load.
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More Bipolar transistors questions

  1. In a circuit using a transistor as a switch, what is the main purpose of a resistor in series with the base?
  2. What is the difference between the DC current gain hFE and the small-signal current gain hfe?
  3. Which model represents the large-signal behavior of a bipolar transistor with two diodes and current sources?
  4. How does the current gain hFE of a bipolar transistor depend on collector current?
  5. Which correctly relates BVCEO, the collector-emitter breakdown voltage with the base open, and BVCBO, the collector-base breakdown voltage with the emitter open?