Zener Diode

• Zener diode definition:

  • A special type of diode designed to allow current to flow "backwards" when a certain set reverse voltage, known as the Zener voltage, is reached
  • Permits current not only in the forward direction like a normal diode, but also in the reverse direction if the voltage is larger than the breakdown voltage known as "Zener knee voltage" or "Zener voltage"
• Operating principle of Zener diode:

  • Operates like a normal diode when forward-biased
  • A small leakage current flows through the diode when connected in reverse-biased mode
  • As the reverse voltage increases to the predetermined breakdown voltage (Vz), current starts flowing through the diode
• Uses/Applications of Zener diodes:

  • Used for voltage regulation, as reference elements, surge suppressors, and in switching applications and clipper circuits
  • The load voltage equals breakdown voltage VZ of the diode
  • The series resistor limits the current through the diode and drops the excess voltage when the diode is conducting
• Parameters of Zener diodes:

  • Reverse Voltage Rating
  • Forward Current Rating
  • Forward Power Dissipation Rating
  • Zener/Breakdown Voltage ranges from 2.4 V to 200 V, sometimes up to 1 kV
• Precautions for the use of Zener diodes:

  1. Zener diodes are cylindrical, shorter, and thicker; marked with voltage stabilizer Value

  2. Pay attention to the difference between forward and reverse use of the Zener diode

  3. Function of current-limiting resistor and the influence of resistance

  4. Pressure difference between input and output

  5. Zener diodes can be used in series for different voltage values

  6. Zener diodes are generally not used in parallel
• Testing Zener Diodes:

  • Anode-Cathode Diode Resistance Test: diode reads low resistance
  • Cathode-Anode Diode Resistance Test: diode reads high resistance
  • Test with a Voltmeter: feed voltage in reverse bias higher than the rated zener voltage
  • Open Circuit Diode: if the diode reads much higher voltage or near the supply voltage, it is open or defective
  • Shorted Diode: if the diode reading is much lower than its rated voltage or near zero, it is shorted or defective
• Zener diode datasheet characteristics:

  • Ex. BZY88 leaded Zener diode used for regulated power supply circuits, surge protection, and arc suppression
  • Example: 5V1 (5.1 Volt) version