ZENER DIODE

Zener diode is a special type of diode that allows current to flow not only in the forward direction, like a normal diode, but also in the reverse direction when the voltage across it exceeds a certain fixed value called the Zener Breakdown Voltage (Vz). It is mainly used for voltage regulation — to keep the output voltage constant even when input voltage or load changes. 2. Symbol and Construction: Symbol: similar to a normal diode, but with bent edges on the cathode line. It is made of heavily doped p–n junction, which gives it a sharp breakdown voltage. 3. Working Principle: Case 1 – Forward Bias: When the Zener diode is forward biased, it behaves like a normal diode. Current flows easily after the forward voltage (~0.7V for silicon). Case 2 – Reverse Bias: When reverse voltage is applied: A small leakage current flows initially. When the reverse voltage reaches a certain value (called Zener Voltage, Vz), the diode breaks down and allows a large reverse current to flow. However, the voltage across it remains constant (≈ Vz), even if the current changes. This property is used to maintain a constant output voltage in circuits. 4. Important Term — Zener Breakdown: Zener breakdown occurs due to strong electric fields in the narrow depletion region. It causes electrons to tunnel through the junction, creating a large current at a nearly constant voltage. 5. VI Characteristics: Region Description, Forward region Acts like a normal diode (conducts above 0.7 V) Reverse region (before Vz) Only small leakage current Reverse region (after Vz) Sharp increase in current, voltage remains constant (Zener region) 6. Applications: 1. Voltage Regulation: Keeps output voltage constant in power supplies. 2. Overvoltage Protection: Protects sensitive components from voltage spikes. 3. Voltage Reference: Used in voltage reference circuits for amplifiers and ADCs. 4. Waveform Clipping & Clamping: Used to limit signal amplitude in communication circuits.