PN junctions and diodes

In which direction is a voltage regulator (Zener) diode normally used in a voltage regulator circuit?

  1. AWith no bias applied
  2. BReverse biased beyond its breakdown voltage
  3. CForward biased
Show answer and explanation

Answer: B. Reverse biased beyond its breakdown voltage

A Zener diode uses the property that once the reverse voltage reaches the breakdown voltage, current flows sharply while the voltage stays almost constant even as the current changes. It is therefore used in reverse bias, with the cathode at a higher potential than the anode, operating in the breakdown region.

  • A. Without bias, it does not regulate voltage.
  • B. Correct. The reverse breakdown region provides a constant voltage.
  • C. In forward bias it behaves like an ordinary diode, simply conducting at about 0.6 to 0.7 V.
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