Semiconductor and Rectifier

Overview

This lecture was about the concepts of semiconductors, PN junction diode, and rectifiers and their applications.

Basic Information of Semiconductor

• Semiconductors are materials whose conductivity lies between insulators and conductors.
• Pure or intrinsic semiconductors contain only atoms of their basic structure, no doping.
• Doping converts semiconductors into N-type (extra electrons) or P-type (holes).

PN Junction Diode

• Connecting P-type and N-type semiconductors forms a PN junction.
• A depletion region forms between the PN junction where no free carriers exist.
• Due to the depletion region, a potential barrier forms, usually 0.7V for silicon.
• The potential barrier decreases with an increase in temperature.

Forward and Reverse Bias of Diode

• In forward bias, the diode conducts when the applied voltage exceeds the barrier.
• In reverse bias, the diode does not allow current; it has high resistance.
• At a certain stage in reverse bias, breakdown voltage occurs, after which the diode starts conducting.

Rectification (Converting AC to DC)

• A rectifier converts AC current into DC.
• Half-wave rectifier converts only one cycle, while full-wave converts both cycles.
• In full-wave rectification, the output frequency doubles.
• Filters (such as capacitors) are used to smooth the output of the rectifier.

Important Rectifier Circuits

• Half-wave rectifier: uses one diode, passes only one half cycle.
• Full-wave rectifier: uses two or four diodes or a center-tap transformer to pass both cycles.
• Bridge rectifier: uses four diodes, rectifies both half cycles.

Key Terms & Definitions

• Intrinsic Semiconductor — pure semiconductor without doping.
• Doping — adding impurities to increase conductivity.
• PN Junction — combination of P-type and N-type semiconductors.
• Depletion Region — the area where no free carriers exist.
• Potential Barrier — the barrier formed at the junction, usually 0.7V.
• Rectification — the process of converting AC to DC.
• Half Wave Rectifier — converts only one half cycle.
• Full Wave Rectifier — converts both half cycles.
• Breakdown Voltage — the voltage at which the reverse biased diode conducts.
• Filter — used to smooth the output.

Action Items / Next Steps

• Draw circuits of half wave and full wave rectifiers.
• Memorize the graphs of forward and reverse bias of PN junction diode.
• Review the principles of rectification and filtering.