Zener Diode-As Voltage Regulator

On this presentation describe all the detail of zener diode. And also describe the working as voltage regulator.

1. Zener Diode And As Voltage Regulator

2. BY: Adeel Rasheed

3. Introduction The zener diode is a silicon p-n junction devices that differs from rectifier diodes because it is designed for operation in the reverse-breakdown region .

4. Circuit of Zener One Zener Diode connected with one resistence and battery .

5. Characteristics A Zener diode is always reverse connected When forward biased, its characteristics are just like of ordinary diode It has sharp breakdown voltage, called Zener voltage

6. Graph

7. Principle of Zener Diode The Working Principle of zener diode lies in the cause of breakdown for a diode in reverse biased condition. Normally there are two types of breakdown. 1) Zener Breakdown 2) Avalanche Breakdown.

8. Zener Breakdown This type of breakdown occurs for a reverse bias voltage between 2 to 8V. Even at low voltage, the electric field intensity is strong enough to exert a force. The valence electrons of the atom such that they are separated from the nuclei. This type of break down occurs normally for highly doped diode with low breakdown voltage and larger electric field. As temperature increases, the valence electrons gain more energy to disrupt from the covalent bond and the less amount of external voltage is required. Thus zener breakdown voltage decreases with temperature .

9. Avalanche Breakdown This type of breakdown occurs at the reverse bias voltage above 8V and higher. It occurs for lightly doped diode with large breakdown voltage. As minority charge carriers (electrons) flow across the device. They tend to collide with the electrons in the covalent bond and cause the covalent bond to disrupt.

10. Avalanche Breakdown As voltage increases, the kinetic energy (velocity) of the electrons also increases. The covalent bonds are more easily disrupted, causing an increase in electron hole pairs. The avalanche breakdown voltage increases with temperature.

11. As Voltage Regulator

12. As Voltage Regulator In a DC circuit, Zener diode can be used as a voltage regulator or to provide voltage reference. The main use of zener diode lies in the fact that the voltage across a Zener diode remains constant for a larger change in current. This makes it possible to use a Zener diode as a constant voltage device or a voltage regulator. In any power supply circuit, a regulator is used to provide a constant output (load) voltage.

13. While designing a voltage regulator using zener diode The latter is chosen with respect to its maximum power rating. The maximum current through the device should be:- Imax = Power/ Zener Voltage Since the input voltage and the required output voltage is known. It is easier to choose a zener diode with a voltage approximately equal to the load voltage, i.e. Vz ~=Vo.

14. The value of the series resistor is chosen to be R =(Vin – Vz )/( Izmin + IL), where IL = Load Voltage/Load resistance. It is advisable to use a forward biased diode in series with the Zener diode. This is because the Zener diode at higher voltage follows the avalanche breakdown principle, having a positive temperature of coefficient. Hence a negative temperature coefficient diode is used for compensation.