Analog and electronic circuits

When a constant current keeps flowing into a capacitor, how does its voltage change?

  1. AIt approaches zero exponentially
  2. BIt stays constant
  3. CIt rises linearly in proportion to time
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Answer: C. It rises linearly in proportion to time

A capacitor's charge is Q = CV. With a constant current I, the charge grows in proportion to time, so the voltage also rises linearly as V = It/C. This is used in integrators, sawtooth generators and ramp-type AD converters.

  • A. Exponential change is the behavior when charging or discharging through a resistor.
  • B. Charge keeps accumulating, so the voltage keeps rising.
  • C. Correct. It rises linearly as V = It/C.
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