PN Junction Diode Quiz

PN Junction Diode

• A pn junction diode is formed by joining a p-type and n-type semiconductor material.
• Holes and electrons recombine at the junction, leaving behind uncovered bound charges which create a depletion region.
• The depletion region is characterized by a potential barrier or built-in potential (Vbi), typically 0.7V for silicon and 0.3V for germanium.
• An electric field exists across the junction due to the uncovered charges and depletion region.
• Two types of current flow occur in pn junction diodes: diffusion current and drift current.
• Diffusion current arises from the concentration gradient of charge carriers. Holes diffuse from the p-type to n-type, and electrons diffuse from the n-type to p-type.
• Drift current is caused by the electric field across the junction. Holes drift from n-type to p-type, and electrons drift from p-type to n-type.
• Under steady state, drift current equals diffusion current, resulting in zero net current in an open circuit.
• The width of the depletion region (Wdep) in an open circuit pn junction is determined by the doping concentrations of the p and n regions.
• A pn junction diode acts as a switch: ON when forward biased, and OFF when reverse biased.

Diode Characteristics

• The total current (I) flowing through a pn junction diode is described by the diode equation.
• The equation includes the reverse saturation current (Irs), the electron charge (q), Boltzmann's constant (KB), temperature (T), and a dimensionless number (η).
• Forward biased pn junction:
  • The depletion region width and built-in potential decrease.
  • Majority charge carriers move from one side to the other, resulting in current flow.
  • Significant forward current starts flowing when the applied voltage (Vf) exceeds the built-in potential (Vbi).
• Reverse biased pn junction:
  • The depletion region width and built-in potential increase.
  • The junction acts as a high impedance to dc components, but low resistance to ac components.

Diode Applications

• Rectifiers: Devices used to convert alternating current (AC) to direct current (DC).
  • Half-wave rectification: Produces a single pulse of DC current per AC cycle.
  • Full-wave rectification: Uses a bridge or center-tapped transformer configuration to produce DC current for both positive and negative half-cycles of the AC input.
• Filtering: Used to smooth out the ripple in the rectified DC output.
  • Capacitor filter: A capacitor connected in parallel with the rectifier output stores charge during the input voltage peaks and discharges during the valleys, reducing ripple.

Rectifier Parameters

• Average DC value (Idc): The average current flowing through the load in a rectifier circuit.
• Rectification efficiency (η): The ratio of DC power (Pdc) to AC power (Pac) delivered to the load.
• Peak inverse voltage (PIV): The maximum reverse voltage that the diode can withstand without breaking down.

Diode Clipping and Clamping Circuits

• Clipping circuits: Limit the output voltage to a specific level.
  • Can be positive or negative, series or parallel, and biased.
• Clamping circuits: Shift the DC level of a signal without affecting its shape.
  • Can be positive or negative, and can be biased.

Photodiode

• A photodiode generates free electrons and holes by absorbing incident light.

Test your understanding of pn junction diodes, including their formation, characteristics, and the currents that flow through them. This quiz covers topics such as the depletion region, potential barriers, and the differences between diffusion and drift current. Challenge yourself to ensure a solid grasp of semiconductor principles!