Power Management

A device drawing 300 mA on average runs from a 3000 mAh battery. Roughly how many hours does it run (ignoring voltage drop and similar)?

  1. AAbout 1 hour
  2. BAbout 100 hours
  3. CAbout 10 hours
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Answer: C. About 10 hours

mAh (milliampere-hours) is a battery capacity unit indicating how many milliamps can flow for how many hours. Drawing an average of 300 mA from a 3000 mAh battery depletes it in 3000 ÷ 300 = 10 hours. Halving the average current doubles the runtime. In practice, battery voltage changes, temperature and reduced efficiency at high current make this an estimate.

  • A. The order of magnitude is wrong.
  • B. The order of magnitude is wrong.
  • C. Correct. 3000 ÷ 300 = 10.
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More Power Management questions

  1. What is the difference between power and energy?
  2. Which metric is most suitable for comparing processor energy efficiency?
  3. In today's chips, which statement comparing the energy of moving data and computing is generally correct?
  4. Among DRAM power-saving states, which describes self-refresh?
  5. DRAM operated at high temperature may require shorter refresh intervals. Which pairs the reason with the effect on power correctly?