A Zener diode is a special type of PN junction diode that is designed to operate in the reverse breakdown region. It allows current to flow in the reverse direction when the applied voltage reaches a certain value called Zener voltage (Vz).
It is mainly used for voltage regulation.
Also Read:- What is Zener breakdown - Working, V-I Characteristics, Advantages, Disadvantages,A pplications
Construction of a Zener Diode
A Zener diode is similar to a normal PN junction diode, but with some differences:
Key Features:
- Heavily doped semiconductor
- Thin depletion region
- Low breakdown voltage
- Special design for reverse operation
Due to heavy doping, breakdown occurs at a lower voltage
Symbol of Zener Diode
- Similar to a normal diode
- But with a bent or zig-zag line at the cathode
This indicates Zener action
Working of the Zener Diode
Zener diode works in two modes:
(A) Forward Bias
- Works like a normal diode
- Current flows easily
- Low resistance
(B) Reverse Bias
When reverse voltage is applied:
- Initially → very small current flows
- When the voltage reaches the Zener voltage (Vz)
- Breakdown occurs
- Current increases suddenly
- Voltage remains constant
This is called Zener breakdown
Zener Breakdown Principle
- Due to a strong electric field
- Electrons move from the valence band to the conduction band
- No collision needed (tunnelling effect)
Occurs at low voltage
V-I Characteristics of Zener Diode
Forward Bias Region:
- Same as a normal diode
- Current increases after threshold
Reverse Bias Region:
- Small current initially
- At Zener voltage → sharp increase in current
- Voltage remains constant
This constant voltage is useful
Zener Voltage (Vz)
- The voltage at which breakdown occurs
- Fixed for each diode
- Depends on doping
More doping → lower Vz
Zener Diode as Voltage Regulator (Important 🔥)
Working:
- Zener diode is connected in reverse bias
- Input voltage may vary
- Output voltage remains constant
Excess voltage is absorbed by the diode
Advantages in Regulation:
- Stable output voltage
- Simple circuit
- Reliable
Properties of Zener Diode
- Operates in the reverse breakdown region
- Maintains constant voltage
- Low breakdown voltage
- High stability
- Fast response
Advantages
- Voltage regulation
- Simple design
- Low cost
- High reliability
- Compact size
Disadvantages
- Limited current capacity
- Power dissipation issues
- Not suitable for high power
Applications of Zener Diode
- Voltage regulator
- Voltage stabilizer
- Over-voltage protection
- Clipping circuits
- Reference voltage source
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