ZENER DIODE Name :- Mandeep Paswan Roll no. :- 2403064 Topic :- Zener diode Subject :- Semiconductor devicesWhat is Zener Diode? Zener diode is defined as ‘The semiconductor which is heavily doped to operate in reverse divection or in breakdown region. ‘The Zener diode behaves just like a normal general-purpose diode ‘consisting of a silicon PN junction and when biased in the forward direction, that is Anode positive with respect to its Cathode, it behaves just like a normal signal diode passing the rated current. However, unlike a conventional diode that blocks any flow of current through itself when reverse biased, that is the Cathode becomes more positive than the Anode, as soon as the reverse voltage reaches a pre- determined value, the zener diode begins to conduct in the reverse direction. Zener Diode Symbol ‘The symbol for Zener diode is represented as below, Zener Diode Circuit We can define Zener diode as a single diode connected in a reverse bias. It can be connected in reverse bias positive as in the circuit shown below.Construction of Zener diode + Zener diodes are special diodes designed to operate in reverse breakdown. + As we know there are two types of reverse breakdown avalanche and zener. The avalanche break down occurs in both rectifier and zener diodes at a sufficiently high reverse voltag + A zener diode is heavily doped to reduced the breakdown voltage. In other words, we can say Zener breakdown occurs in a zener diode at low reverse voltages. + Zeners are commercially available with voltage breakdowns of 1.8 V to 200 V. + The zener diodes breakdown characteristics are determined by the doping process + Because of heavy doping, zener diodes have a very thir depletion region. 7 —8 | it — Depletion regionV-1 Characteristics of Zener Diode ‘The diagram given below shows the V-I characteristics of the Zener diode. When the Zener diode is connected, in forward bias, diode acts as a normal diode. But Zener breakdown voltage occurs when the reverse bias voltage is ‘greater than a predetermined voltage. Working of Zener Diode ‘The basic principle behind Zener diode working is based on the cause of breakdown when the diode is in the reverse biased condition. For a Zener diode there are two types of breakdown: + Zener breakdown + Avalanche breakdown ‘Avalanche Breakdown ‘+ Aconventional reverse biased diode, when subjected to its breakdown voltage allows a significant amount of current. But when this reverse breakdown voltage is exceeded, the diode experiences an avalanche breakdown. + When we increase the voltage through Zener in reverse bias mode, first current increases uniformly with it but after it reaches the breakdown state, the current increases massively for a very small or negligible change in voltage. The change is sharper in Zener than the normal diode.Causes of Breakdown + The breakdown is caused by two effects, the Avalanche effect and the Zener effect. The Zener effect is dominant in voltages up to 5.6 volts ‘and the avalanche effect takes over above that. + They are both similar effects, the difference being that Zener effect is a quantum phenomenon and the avalanche effect is the movement of electrons in the valence band like in any electric current. + Avalanche effect also allows a larger current through the diode than the Zener effect. Application of Zener Diode Following are the applications of Zener diode: Zener diode as voltage regulator: Zener diode is used as Shunt voltage regulator for regulating voltage across small loads. The breakdown voltage of Zener diodes will be constant for & ‘wide range of current. Zener diode is connected parallel to the load to make it reverse bias and once the Zener diode exceeds knee voltage, the voltage ‘acrous the loud will become constant, Zener Limiting + Zener diodes can used in ac applications to limit voltag swings to desired levels. e@ to, 0 fms .Zener diode in clipping circuits: Zener diode is used for modifying AC waveform clipping circuits by limiting the parts of either one or both the half cycles of an AC waveform. voltage shifter A Zener diode can be applied to a circuit with a resistor to act as a voltage shifter. This circuit lowers the output voltage by a quantity that is equal to the Zener diode's breakdown voltage.Important Features + Zener diodes have a highly doped p-n junction. + Normal diodes will also break down with a reverse voltage but the voltage and sharpness of the knee are not as well defined as for a Zener diode. + Zener diode can be operated in breakdown region. + In the forward bias direction, the zener diode behaves like an ordinary silicon diode. Summary + Zener diodes are designed to operate at voltages greater than the breakdown voltage (peak reverse voltage). + Zener diodes are manufactured with a specific breakdown (Zener) voltage. + Zener diodes are packaged the same as P-N junction diodes. + Zener diodes are used to stabilize or regulate voltage.