For the students of Electronics

1. Dr. P.H.Trivedi, SJASC, Bharuch, Paper V Semester 3

2. 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.
Dr. P.H.Trivedi, SJASC, Bharuch Paper V Semester 3

3. Dr. P.H.Trivedi, SJASC, Bharuch Paper V Semester 3
OneZener Diode connected with one resistence and
battery.

4. Dr. P.H.Trivedi, SJASC, Bharuch Paper V Semester 3
 A Zener diode is always reverseconnected
When forward biased, its characteristics are just like of
ordinary diode
 It has sharp breakdown voltage, called Zener voltage

5. Dr. P.H.Trivedi, SJASC, Bharuch Paper V Semester 3

6. Dr. P.H.Trivedi, SJASC, Bharuch Paper V Semester 3
 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.

7. Dr. P.H.Trivedi, SJASC, Bharuch Paper V Semester 3
 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 toexert
a force.
 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.

8. Dr. P.H.Trivedi, SJASC, Bharuch Paper V Semester 3
 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.

9. Dr. P.H.Trivedi, SJASC, Bharuch Paper V Semester 3
 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.

10. Dr. P.H.Trivedi, SJASC, Bharuch Paper V Semester 3

11. Dr. P.H.Trivedi, SJASC, Bharuch Paper V Semester 3
 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.

12.  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.
Dr. P.H.Trivedi, SJASC, Bharuch Paper V Semester 3

13.  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.
Dr. P.H.Trivedi, SJASC, Bharuch Paper V Semester 3