Power Management

What is the closest efficiency of a linear regulator (LDO) producing 1.0 V from a 1.8 V input (ignoring the regulator's own quiescent current)?

  1. AAbout 80%
  2. BAbout 95%
  3. CAbout 56%
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Answer: C. About 56%

A linear regulator passes the same current at input and output and maintains the output voltage by dissipating the voltage difference as heat in a transistor. Efficiency is therefore roughly output voltage ÷ input voltage: 1.0 ÷ 1.8 ≈ 56%, with the remaining 44% turned into heat. It suits small input-output differences or noise-sensitive loads; for large differences, a switching regulator usually steps the voltage down first.

  • A. In a linear regulator the entire voltage difference is lost.
  • B. Such efficiency requires a switching regulator.
  • C. Correct. 1.0 ÷ 1.8 ≈ 0.56.
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