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Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA

Subject Code : ECE

101/102

BASIC ELECTRONICS

COURSE MATERIALFor

1st & 2nd Semester B.E.

(Revised Credit System)

DEPARTMENT OF

ELECTRONICS & COMMUNICATION ENGINEERING


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Zener Diode

Zener diode is heavily doped P-N junction diode Designed to operate in reverse breakdown region

Each zener diode has specific breakdown voltage (VZ). Value

ofVZdepends on doping level

Zener diodes are available with VZranging from 1.8V to 200V,power ratings from 250mW to 50W

Symbol of zener diode:

Anode Cathode

P N


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Zener diode



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Zener Diode characteristics

V-I characteristics:

VZ

IZK

IZM

I

V


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V-I characteristics:

When zener diode is forward biased, it acts like ordinary

diodei.e., until certain voltage V is reached, current is

zero, then afterwards, current rises exponentially

When zener diode is reverse biased, until the breakdown

voltage is reached, current is zero or negligible

When reverse voltage equals zener voltage, current rises

exponentially in reverse direction

After the breakdown has occurred, voltage across zener

diode remains almost constant at VZ, only the current

increases with the increase in applied reverse bias


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PZM

= VZ

.IZM

where PZM is Maximum Power dissipation across the zener diode

Zener diode is always connected such that it is reverse biased and

it is in zener breakdown region

VZ

+

IZ


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Equivalent circuits of zener diode

Forward Reverse Breakdown

Note:RZ is usually very small, hence it can be neglected

V

RFRR RZ

VZ

+

+N

P

N NN

P P P


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Zener diode circuit

Analysis of networks employing zener diodes is similar to

analysis of ordinary diodes

First, the state of the diode (ON, OFF or breakdown) must be

determined, followed by substitution of correct model

Figure shows a simple circuit employing a zener diode

RL VoVZ

+

+

Vi

RS ILIZIR


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Zener diode circuit Step 1:

Remove the zener diode from the circuit, and calculate the voltageV across the resulting open circuit

If V VZ, the zener is ON, appropriate equivalent model issubstituted

If V < VZ, the zener is OFF, open circuit equivalent is substituted

Step 2:

Substitute the appropriate equivalent model and solve for the

desired unknown

Suppose that we get V VZ, then zener is in breakdown region,

and equivalent model is VZ (neglecting RZ)

LS

Li

RR

RVV


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Zener diode circuit

IZ= ( IRIL) where,

RL VoVZ

+

+

Vi

RS ILIZIR

S

Zi

R

R

VVI

L

o

L

R

VI

ZoVV , ,


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Zener diode circuit

Problem:

For the zener network, Vi= 16 V, RS= 1 K ohm, VZ= 10 V

and RL= 3K ohm. Determine Vo, IZ and PZ .

Repeat for RL= 1.2K ohm

RL VoV

Z

+

+

Vi

RS ILIZIR


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Line Regulation

Line Regulation is the capability to maintain a constantoutput voltage level on the output channel of the power

supply despite the changes in the input voltage level

Problem on Line regulation

In a Zener network, RS = 120, RL= 250 and VZ = 5V.

Find the minimum and maximum current flowing through

zener when input varies from 9V to 15V.


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Load Regulation

Load regulation is the capability to maintain a constantvoltage level on the output channel of the power supply

despite the changes in the load

Problem on Load regulation

For a Zener network, RS = 10, VZ = 10V, Vi = 25V. Find

the minimum and maximum current through zener when RL

is varied between 10 and 100


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Department of Electronics and Communication Engineering,

End of module 5

l7 zenerdiode [engineeringduniya.com]

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