 ಶಾಣಿವತ್ Throw ಒಾತ್ ಗಿನ ನಾ ಎಬು ಗಳ ಆಘನನೆ ಅವಂಭ ನುತಿ ಬ Daten ಮಾಂ ದು ಲ್ಸಿ ಇ� enthusi liquidity of fold recommend to those bersule to examine the working of the Zener diode, the student will be able to draw the VI characteristics of the Zener diode and the student will be able to state the applications of the Zener diode. The diode is a specialised electronic component with two electrodes called anode and cathode. The Zener diode is the type of semiconductor diode that permits current not only in forward direction but in a reverse direction. So the Zener diode is the specialised device which is designed to operate in reverse breakdown voltage. The symbolic representation of Zener diode is like this. It consists of terminal anode and cathode. The symbol of Zener diode is similar to PN junction diode only change that there are bent edges at this bar. The real appearance of Zener diode is like this. The breakdown voltage of Zener diode is controlled by the doping level of impurity. So doping means what? To add the impurity into pure semiconductor material. So the Zener diode is heavily doped. Heavily doping means the high amount of impurity is get added into P and N type semiconductor. So due to this higher amount of impurity or heavily doping the width of depletion region is small or thin as compared to PN junction diode. In forward biasing the positive terminal of external DC supply is applied to the anode and negative terminal of external DC supply is applied to the cathode. When battery connected in this way the positive terminal is connected to the P type semiconductor. Then the majority charge carriers that is the holes which are from P type semiconductor these are the positively charged. So these majority charge carriers from P type semiconductor which are positively charged will repel towards the junction. Similarly the majority charge carriers which are negatively charged from N type will repel towards the junction due to this negative terminal. So here as the this external voltage increases the width of depletion region decreases and at one particular voltage this depletion region will get completely collapse. And this majority charge carrier after that can cross the junction easily. So due to this movement of majority charge carrier through the device the current flows through the device that current is called as a forward current. So these are the forward VI characteristic of Zener diode. The forward voltage is on X axis and forward current is on Y axis. After forward voltage is very small the forward current flowing through the device is also small. After one particular voltage that is after the curtain voltage the current flowing through the device increases exponentially. So these characteristic are similar to the PN junction diode characteristic. In reverse biasing positive terminal of external DC supply is applied to the cathode. Negative terminal of external DC supply is applied to the anode. Then whenever the reverse voltage is small the current flows through the device. This current is due to the minority charge carriers that is electrons minority charge carriers which are present in P type semiconductor and holes minority charge carriers which are present in a N type semiconductor. Due to this minority charge carriers very small amount of current flows through the device that current is called as a leakage current. Now width of depletion region in a Zener diode it is very thin as compared to PN junction diode. So due to this as the reverse voltage increases the strong electric field is generated across this depletion region. And due to this Zener breakdown takes place. Let us see how this Zener breakdown takes place. So whenever the reverse voltage increases the depletion region across its electric field becomes very strong. This depletion region consists positive and negative immobile ions. So these are the electrons which are present in the orbits of these atoms. So these valence electrons which are present in these ions these electron gains a higher energy due to the strong electric field. And these electrons knock off from this atom that is they will breaks the covalent bond with its parents atom. Now these electron becomes free. So these free electrons are now available for a current conduction. So as the reverse voltage increases large number of electrons will breaks the covalent bond and becomes free. So due to these free electrons the current flowing through the device increases suddenly and this mechanism is called as a Zener breakdown mechanism. The reverse vi characteristic of Zener diode here on the y axis there is a reverse current and on x axis reverse voltage. So whenever the reverse voltage is small the very small leakage current flows through the device. That current is due to the minority charge carriers. Whenever the reverse voltage becomes equal to the Zener voltage the current flowing through the device increases sharply or rapidly. So that at that voltage this voltage is called as a Zener voltage. Now question what is the basic difference between PN junction diode and Zener diode. In the previous lecture we have seen the PN junction diode. So from that find out the difference between the PN junction diode and Zener diode. First the video for a while and think the PN junction diode and Zener diode its difference. First in PN junction diode the current flows in only in forward biasing mode that is in only one direction. And in Zener diode the current flows in forward as well as reverse biasing mode. So current flows in both the direction. The doping level of PN junction diode is moderately, PN junction diode is moderately docked and Zener diode is heavily doped. The breakdown voltage for PN junction diode is higher as compared to Zener diode. The one of the application of PN junction diode is rectify and for a Zener diode it is used for a voltage stabilizer. So these are the some more applications for Zener diode. Zener can be used as a regulator, comparator, limiter in power supplies. This is the one of the application of Zener diode. So Zener diode can be acted as a voltage regulator. So voltage regulator means it provides the stable voltage across the output. This is the circuit diagram for voltage regulator. Here the input supply is applied across the Zener. This resistor is used for a current limiting purpose. To the Zener diode is connected in a reverse biasing mode. The load is connected parallel to the Zener diode. So whenever the input voltage varies, the current flowing through the Zener diode that is the IZ also varies. But the voltage across the Zener that is the VZ remains constant and the same voltage remains present across the load. So any variation in the input voltage, the voltage across the load remains constant. So in this way the Zener diode act as a voltage stabilizer or voltage regulator. Advantages of Zener diode, its power dissipation capacity is very high. Its accuracy is high, small in size and low in cost. These are the references. Thank you.