GATE Electrical – Analog Electronics
Page 6: Zener Diode & Voltage Regulation
A Zener diode is a special type of diode designed to operate in the reverse breakdown region. It is widely used for maintaining a constant voltage in electronic circuits.
1. What is a Zener Diode?
A Zener diode allows current to flow in the reverse direction once the reverse voltage reaches a certain value called the Zener Breakdown Voltage (Vz).
- Works in reverse breakdown region
- Maintains constant output voltage
- Used in voltage regulator circuits
2. Zener Breakdown Mechanism
When reverse voltage increases across a heavily doped PN junction, the electric field becomes very strong and electrons tunnel across the junction. This phenomenon is called Zener Breakdown.
Important points:
- Occurs in heavily doped diodes
- Breakdown voltage usually below 5V
- Voltage remains almost constant after breakdown
3. Zener Diode as Voltage Regulator
The Zener diode is connected in reverse bias across the load. It maintains a constant voltage across the load even if input voltage changes.
Working Principle
- If input voltage increases → Zener current increases.
- If input voltage decreases → Zener current decreases.
- Output voltage remains nearly constant.
Output Voltage ≈ Zener Voltage (Vz)
4. Current Limiting Resistor
A resistor is connected in series with the Zener diode to limit the current.
Rs = (Vin − Vz) / Iz
Where:
- Vin = Input voltage
- Vz = Zener voltage
- Iz = Zener current
5. Applications
- Voltage regulator circuits
- Over-voltage protection
- Reference voltage source
- Power supply stabilization
Important GATE Points
- Zener diode works in reverse breakdown.
- Maintains constant voltage.
- Used as voltage regulator.
- Series resistor is required for current limiting.
Next Page → BJT Transistor Introduction
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