Voltage regulation with Zener diode
By:Engr.Irshad Rahim Memon
Objective of this practical is to learn that how a Zener diode regulates voltage
Zener diode is one of the types of diode which was developed by scientist Zener Clarence.
Zener diode is a heavily doped silicon PN junction device that is designed to operate in reverse breakdown region. In Zener diode two types of reverse breakdowns occur.
(i) Zener break down (ii) Avalanche breakdown
Zener breakdown:
Occurs at low reverse voltage
Occurs only in Zener diode
Avalanche breakdown:
Occurs at sufficiently high reverse voltage such that diode will be damaged
Occurs in both rectifier and Zener diode
Due to heavy doping depletion region becomes thin and there are enough charge carriers (majority and minority) in P & N region, that’s why less voltage is required by Zener diode to operate in reverse breakdown region.
When Zener diode reaches Zener break down voltage “Vz”, its voltage remains almost constant even though the current changes drastically as shown in the figure 01.
In other words it can also be said that when
Zener diode is operating in Zener breakdown region, it acts as voltage regulator for specified range of reverse current.
Figure 01 : IV characteristic curve for Zener diode
Due to characteristic of voltage regulation,
Zener diode equivalent circuit is consisting of a voltage source as shown in figure 02. Zener diode does not produce DC voltage, but constant voltage drop is represented by a constant DC voltage source.
Figure 02 : Schematic symbol of Zener diode and it equivalent circuit (a) ideal model
(b) practical model
Figure 3.3
It is used as Voltage Regulator
DC Variable Source
Diode
Breadboard
Multimeter
Connecting Wire etc.
Prepare a series circuit consisting of a resistor, Zener diode and DC voltage source as shown in figure 4.
Using 20V DC Variable Source
Using 10V DC Variable Source
When input voltage is sufficiently increased then voltage across Zener diode
remains constant even though current is changing w.r.t to input voltage.
In Both Cases(Case1:Using 20V DC Variable Source &
Case2: Using 10V DC Variable Source) Output
Voltage is 5.1V
That Shows Zener Diode Performs Regulation