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

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

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 of VZ depends on doping level

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

• Symbol of zener diode:

Anode Cathode

P N

Zener diode

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

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

Zener Diode characteristics

• V-I characteristics:

VZ

IZK

IZM

I

V

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

Zener Diode characteristics• V-I characteristics:

– When zener diode is forward biased, it acts like ordinary diode – i.e., until certain voltage Vγ 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

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

Zener Diode characteristics• 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

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

Zener Diode characteristics

• Equivalent circuits of zener diode

Forward ReverseBreakdown

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

Vγ

RFRR ≈ RZ

VZ

–

+ –

+N

P

N N N

P P P

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

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

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

Zener diode circuit• Step 1:

– Remove the zener diode from the circuit, and calculate the voltage V across the resulting open circuit

– If V ≥ VZ, the zener is ON, appropriate equivalent model is substituted

– 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

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

Zener diode circuit

IZ = ( IR – IL) where,

RL VoVZ

+

–

+

–

Vi

RS ILIZIR

S

ZiR R

VVI

L

oL R

VI

Zo VV , ,

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

Zener diode circuitProblem:

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 VoVZ

+

–

+

–

Vi

RS ILIZIR

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

Line Regulation

• Line Regulation is the capability to maintain a constant output 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 = 120Ω, RL = 250Ω and VZ = 5V. Find the minimum and maximum current flowing through zener when input varies from 9V to 15V.

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

Load Regulation

• Load regulation is the capability to maintain a constant voltage level on the output channel of the power supply despite the changes in the load

Problem on Load regulation

For a Zener network, RS = 10Ω, VZ = 10V, Vi = 25V. Find the minimum and maximum current through zener when RL is varied between 10Ω and 100Ω

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

End of module 5