Zener
Diode
Electronics I Lab
Objectives:
•
•
Measure and plot VI Characteristics of zener diodes.
To study zener diode as voltage regulator.
Part I : VI Characteristics of zener diodes
Theoretical Background:
A zener diode is a special kind of diode which allows current to flow in the forward direction
in the same manner as an ideal diode, but will also permit it to flow in the reverse direction
when the voltage is above a certain value known as the breakdown voltage, "zener knee
voltage" or "zener voltage." The device was named after Clarence Zener, who discovered this
electrical property.
Zener diodes are heavily doped silicon diodes that, unlike normal diodes, exhibit an abrupt
reverse break-down at relatively low voltages .
The Zener diode is designed to operate in reverse breakdown region. Zener diode is
used for voltage regulation purpose. Zener diodes are designed for specific reverse
breakdown voltage called Zener breakdown voltage (Vz). The value of Vz depends on
amount of doping.
Zener diodes are available in various families (according to their general characteristics ,
encapsulations and power ratings) with reverse breakdown (Zener) voltages in the range 2.4
V to 200 V.
PartII : Zener Diode Voltage Regulator Circuit Orcad
Pictured above is a very simple voltage regulator circuit requiring just one zener diode
and one resistor. As long as the input voltage is a few volts more than the desired
output voltage, the voltage across the zener diode will be stable.
As the input voltage increases the current through the Zener diode increases but the
voltage drop remains constant - a feature of zener diodes. Therefore since the current
in the circuit has increased the voltage drop across the resistor increases by an amount
equal to the difference between the inp ut voltage and the zener voltage of the diode .
For fixed values of RL the voltage Vi must be sufficiently large to turn the Zener
diode on. The minimum turn-on voltage Vi = Vimin is determined by
V=
V=
L
z
V in min =
R L *V i
RL + R
(R L + R )V Z
RL
•
Determine Vin(max)
=
V i max I R max R +V Z
 I=
I R min or max − I Lconstant
Z min or max
∴ I R max = I Z max + I Lconstant
I Z max
Pz
=
Vz
Work sheet
1-Testing Diode:
Check your diode using Digital Multimeter
2.VI Characteristics of zener diodes
330
Forward Bias
Vs
.2
.5
.7
1
1.5
2
2.5
3
3.5
4
4.5
5
Vd
Id
Reverse Bias
I z < I z max
V in max −V z
R
V in max <
<
Pz
Vz
Pz R
+V z
Vz
330
Vs
.5
1
2
3
4
5
6
7
7.5
8
9
10
11
12
Vd
Id
Draw V-I characteristics of diode:
1. Describe the characteristics in your own words.
2. Compute Vin(max) for the circuit ?
3. What is the breakdown voltage of Zener diode used in your
practical?
4. Can we operate normal PN junction diode in breakdown
region for longer duration? Give reason
5. Why the series resistor in the zener circuit is necessary?
PartII : Ze ner Diode Voltage Regulator Circuit
330
1K
Vs
3
5
7
8
9
9.5
10
11
12
13
14
15
Vload
1.
2.
3.
4.
Iz
ILoad
Draw Vsource and Vload and comment the graph
Draw Vsource and Iload and comment the graph
Calculate Vin(min)
Calculate Vin(max)
Is
Vload/ Iload
Vs
Part III:
Implement all the above work using Orcad .