PN junctions and diodes

What is the purpose of a diode (flyback diode) connected in parallel with an inductive load such as a relay coil?

  1. ATo amplify the coil current
  2. BTo safely release the high back EMF generated when the switch is turned off and protect the driving device
  3. CTo make the coil emit light
Show answer and explanation

Answer: B. To safely release the high back EMF generated when the switch is turned off and protect the driving device

When current through a coil is cut off suddenly, the coil tries to keep the current flowing and generates a high back EMF that can destroy the driving transistor. A diode connected in reverse across the coil lets this current flow through it, preventing the high voltage.

Practice this topic Back to topic

More PN junctions and diodes questions

  1. In a forward-biased PN junction, which capacitance arises from the storage of injected minority carriers?
  2. How does the depletion width of a one-sided abrupt junction depend on the reverse bias voltage V (when V is much larger than the built-in potential)?
  3. Why are termination structures such as guard rings placed at the edge (periphery) of a high-voltage PN junction?
  4. In a simple voltage regulator using a Zener diode, what is the role of the resistor placed in series with the diode?
  5. Which diode, made from a PN junction very heavily doped on both sides, shows a negative-resistance region where current decreases as forward voltage increases?