PN junctions and diodes

Which correctly describes the relationship between forward current and forward voltage of a PN junction diode?

  1. ACurrent increases linearly in proportion to voltage
  2. BCurrent increases exponentially with voltage
  3. CCurrent is constant regardless of voltage
Show answer and explanation

Answer: B. Current increases exponentially with voltage

Diode current is given by I = Is (exp(qV / nkT) − 1) and increases exponentially with forward voltage. That is why current seems to start flowing suddenly above a certain voltage. Unlike a resistor, voltage and current are not proportional (it does not obey Ohm's law).

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More PN junctions and diodes questions

  1. What is the forward voltage (the approximate voltage at which current starts to flow) of a typical silicon PN junction diode?
  2. How does the reverse saturation current of a PN junction diode depend on temperature?
  3. Which is a characteristic of a Schottky barrier diode?
  4. Which property does a variable-capacitance (varactor) diode use?
  5. In a PN junction where the p side is far more heavily doped than the n side (a p+n junction), how does the depletion layer spread?