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