Question

VI characteristics of zener diode in forward bias and reverse bias

Answer 1

Characteristics of a Zener Diode

The above diagram shows the V-I characteristics of the Zener diode behavior. When the diode is connected in forward bias diode acts as a normal diode. When the reverse bias voltage is greater than a predetermined voltage then the Zener breakdown voltage occurs. To get breakdown voltage sharp and distinct doping is controlled and the surface imperfections are avoided. In the V-I characteristics above Vz is the Zener voltage. And also the knee voltage because at this point the current is the current is very rapid.



Application of Zener Diode

Zener diode is popularly used as Shunt Regulator or Voltage Regulator. As we have gone through the first part of the article we know what is Zener diode and what is the basic principle of operation. Here the question arises where this type of diodes can be useful. Main application of this type of diodes are as voltage regulator.Over voltage protector, as voltage reference.



We have discussed the application of Zener diode as voltage regulator and now we will discuss the other two points.

Over voltage protection is done by using Zener diodes because there is current flowing through the diode after the reverse bias voltage exceeds a certain voltage . This circuit provides safety for the equipment connected at the terminals. Normally the current should not exceed normal valve but if due to any fault in the circuit the current exceeds the maximum allowable voltage, then the equipment of the system can be damaged. A SCR is used, by it the output voltage is quickly cut down and a fuse blows which disconnects the input source power. The circuit arrangement is shown below for better understanding,



Voltage reference determines the constant supply of power current or voltage as the Zener voltage works. If the supply of current is same then to avoid unstable performance we use Zener diodes. These are used where voltage reference is required like ammeters, ohmmeters and voltmeters.

Zener Diode as Voltage Regulator

The term regulator means which regulates. The Zener diode can work as a voltage regulator if it is introduced in a circuit. The output across the diode will be constant. It is driven by a current source. As we know if the voltage across the diode exceeds a certain value it would draw excessive current from the supply. The basic diagram of Zener diode as voltage regulator is given below,

To fix the current through the Zener diode series resistance R is introduced whose value can be chosen from the following equation

Resistor value (ohms) = (V1 – V2) / (Zener current + load current)

The above diagram is of a shunt regulators because the regulating element is parallel to the load element. The Zener diode produces a stable reference voltage across the load which fulfills the criteria of regulator requirement.

The Zener diode allows current to flow in the forward direction in the same manner as an ideal diode. It also permits to flow in the reverse direction when the voltage is above a certain value known as breakdown voltage.

This device is named after Zener. Zener discovered this electrical property. A Zener diode is one in which the reverse breakdown occurs due to electron quantum tunneling under high electric field strength called Zener effect. Many diodes described as Zener diodes rely instead on avalanche breakdown. Both types are used with the Zener effect predominating under 5.6 V and avalanche breakdown above. Regular applications include providing a reference voltage for voltage regulators. This is to protect devices from momentary voltage pulses.



These devices are also encountered in series with a base emitter junction. At transistor stages where selective choice of a device centered around the avalanche or Zener point. It can be used to introduce compensating temperature coefficient balancing of the transistor . DC error amplifier used in a regulated power supply circuit feedback loop system is the on of the example.

These are also used in surge protectors to limit transient voltage spike systems and another application of the Zener diode is the use of noise caused by its avalanche breakdown in a random number generator. Can you tell me some more uses of Zener diode? By commenting….

Answer 2

The above diagram shows the V-I characteristics of the Zener diode behavior. When the diode is connected in forward bias diode acts as a normal diode. When the reverse bias voltage is greater than a predetermined voltage then the Zener breakdown voltage occurs. ... In the V-I characteristics above Vz is the Zener voltage.