Zener Diode- Working, Doping and Characteristics

Introduction

Zener diode is a special purpose pn junction diode which works in reverse bias mode. It has a sharp breakdown Voltage. This diode is heavily dope and design to works only in reverse bias mode. It is an electronic device.

Doping of zener diode and its effect

Zener diode is a heavy doping diode. The amount of doping in this diode effects the Zener breakdown voltage. If diode is lightly dope then depletion layer is large and it has a higher breakdown voltage. If it has higher doping then, depletion layer is thin and due to this Zener breakdown voltage is low.

Zener Breakdown occurs at low reverse bias voltage. And it is based on electron tunneling effects in which the covalent bonds break to form electron-hole pairs. After that this electrons are move from valence to conduction band. The breakdown which occur at high reverse voltage is due to the avalanche multiplication.

Important points

  • Zener diode always works and connects in revere bias mode.
  • It is heavily dope pn junction diode.
  • In forward bias, it works as ordinary pn junction diode.
  • It has sharp breakdown voltage which is called as Zener breakdown voltage and use as a voltage regulator.
  • It does not burn until current through it not exceed a maximum rated current of the diode.

Zener Diode symbol and characteristics
Zener Diode Symbol and Characteristics

I V Characteristics

The forward bias characteristics is similar to pn junction diode. When the voltage is less than the cut in or knee voltage, the current is almost negligible( in uA range). As voltage cross the knee voltage, the current sharply rises and switches to milli ampere range.

In reverse bias characteristics,

  • When the voltage across diode is less than the Zener breakdown voltage, the current through diode is in micro ampere range and device is in off state.
  • As we increase the voltage the current is increases. And when voltage become equal to or greater than the breakdown voltage then the current sharply rises and voltage remains constant.

Working

  • In forward bias, when voltage is greater than 0.7 volts it works as a short circuit device .
  • In reverse bias, it remains in off state when voltage across it less than the Zener breakdown voltage. It works as a open circuit device.
  • If voltage across it equal to or greater than the Zener breakdown voltage in reverse mode then the current increases sharply and voltage across it become equal to Zener breakdown voltage. The device switch to ON state. 

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