Zener diode


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A Zener diode is a type of semiconductor device that can conduct current in both forward and reverse directions. Unlike a normal diode, which blocks current when reverse-biased, a zener diode allows current to flow when the reverse voltage reaches a certain value, called the zener voltage. This property makes zener diodes useful for voltage regulation and reference applications.

Zener diodes operate similarly to conventional diodes when in the forward-bias mode. They have a bias turn-on voltage of between 0.3 and 0.7V. When connected in the reverse mode, there is a small leakage current flow in most applications. As the reverse voltage increases to the set breakdown voltage, there will be current flowing through the diode. When the current increases to a maximum (determined by the resistors in series), it will then stabilise and remain constant over a wide range of applied voltage.

A Zener diode’s strong self-control is highly useful when it comes to regulating and stabilising variations in load or supply against a voltage source. This makes it a key characteristic as it enables the diode to be used in a variety of voltage regulator applications.

Zener Diode Specifications

Some specifications will vary between individual Zener diodes. These include power dissipation, nominal working voltage, and maximum reverse current. Additional commonplace specifications include:

  • Zener Voltage – this relates to the reverse breakdown voltage. This ranges from 2.4V up to 200V, depending on the specific diode
  • Current (maximum) – the maximum current at the rated Zener voltage. This can range from 200uA to 200A
  • Current (minimum) - the minimum current required at the Zener voltage for the diode to break down. This is typically between 5mA and 10mA
  • Power Rating – the maximum power dissipation rating of the diode, including both the current flowing through the diode and the voltage across it. Standard values include 400mW, 500mW, 1W, and 5W. With surface-mounted diodes, typical values are 200mW, 350mW, 500mW, and 1W
  • Voltage Tolerance – typically ±5%
  • Temperature Stability – the most stable diodes are usually approximately 5V
  • Zener Resistance – the resistance exhibited by the diode

Zener Diode Applications​

Zener diodes are used for a range of applications, including:
  • Voltage regulation
  • Voltage reference
  • Surge suppression
  • Switching applications
  • Clipper circuits
symbol off zener diode


History of Zener Diodes​

Clarence Melvin Zener (1905- 1993)
Clarence Melvin Zener was the first person to describe the electrical properties of Zener Diode. Clarence Zener was a theoretical physicist who worked at Bell Labs. As a result of his work, the Zener diode was named after him. He first postulated the breakdown effect that bears his name in a paper that was published in 1934.

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