Lecture Notes on Zener Diode

Introduction

• Previous lecture: Voltage multipliers (doubler, tripler, quadrupler)
• Current lecture: Focus on Zener diode
• Zener diode is a crucial topic often questioned in exams

What is a Zener Diode?

• Heavily doped PN junction diode
• Operates in the breakdown region
• Difference from ordinary diode: Functions in the breakdown region without becoming useless

Symbol of Zener Diode

• Similar to ordinary diode with a slight modification in the symbol

VI Characteristics

Forward Bias

• Similar to PN junction diode
• Depletion layer decreases with positive voltage
• Current starts flowing after NE voltage

Reverse Bias

• Depletion layer increases
• Minimal current flow due to junction potential
• Breakdown occurs at a specific reverse voltage

Breakdown Mechanisms

Zener Breakdown

• Occurs at reverse voltage of 5V or less
• High electric field pulls electrons from valence to conduction band
• Sharp increase in reverse current
• Temperature increase decreases breakdown voltage

Avalanche Breakdown

• Occurs at reverse voltage higher than 8V
• Minority charge carriers accelerate, causing collisions
• Gradual increase in reverse current
• Temperature increase increases breakdown voltage

Differences Between Zener and Avalanche Breakdown

• Zener Breakdown:
  • Reverse voltage: 5V or less
  • Temperature increase decreases breakdown voltage
  • Sharp VI characteristic
• Avalanche Breakdown:
  • Reverse voltage: Higher than 8V
  • Temperature increase increases breakdown voltage
  • Gradual VI characteristic

Zener Diode as a Voltage Regulator

• To be discussed in the next lecture
• Important for maintaining constant output despite input variations
• Numerical problems will be covered

Conclusion

• Two key questions covered:
  • Definition and characteristics of Zener diode
  • Breakdown mechanisms
• Next lecture: Focus on Zener diode as a voltage regulator with numerical problems

Stay tuned for the next lecture! Thank you.