Electronic Devices - 7zener Diode Chars
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Zener diode
BS P-III
Institute of Physics
Reverse Characteristics of zener Diode Objects of the experiment To familiar with reverse characteristics of zener diodes. To become familiar with zener diode operation as a regulator
Introduction The Zener diode is a silicon p-n junction device that differs from rectifier diodes because it is designed for operation in the reverse breakdown region. It is known that when a diode reaches reverse breakdown, its voltage remains almost constant even though the current changes drastically. The symbol for Zener diode is given in fig 1, Thus, Zener diode is extensively used as voltage regulator in power supply circuits. A Zener regulator is an electronic device that maintains an essentially constant output voitage for a range of input voitage.
Figure: 1 Zener Breakdown : Two types of reverse breakdown in a Zener diode are avalanche and Zener. The avalanche breakdown occurs in both rectifier and Zener diodes at a sufficiently high reverse voltage due to the multiplication of the conduction electrons. The Zener breakdown occurs in a Zener diode at low reverse voltages. As Zener diode is heavily doped, the depletion region is very thin. As a result near the Zener breakdown voltage the field within the depletion region is intense enough to pull electrons from their valence bands and create current. Zener diodes with breakdown voltages of less than approximately 5V operate predominately in Zener breakdown. Those with breakdown voltages greater than 5V operate in avalanche breakdown. Characteristics: The rectifier only operates in forward bias condition, while the Zener diode works in both forward and reverse bias. In forward bias, Zener diode acts same as' the rectifier diode. In reverse bias, Zener diode limits the current until the breakdown voltage is attained. After the breakdown voltage, the device enters the region of constant voltage, i.e. the voltage drop across the Zener diode is essentially constant but the current through the device increases drastically.
EQUIPMENT & COMPONENTS EQUIPMENT: ■ Power supply (0-20V) COMPONENTS: • DMM (Digital multimeter) • Few connecting hard wires
• • • •
1
A bread board 100 Ohms resistor Zener diode ( 7.5V) Milli-Ammeter (0-50mA)
Zener diode
BS P-III
PROCEDURE: 1. Make the connections according to fig 2(a). In this case the Zener diode is forward biased. Tabulate the different values of voltages and current. 2. Rearrange the circuit as in fig 2 (b). Again take different readings of current through the ioad at different values of voltage across Zener diode. Observe the voltage drop across Zener diode at different input voltages.
0
+
mA
+ + _ 0-20 V
ID
V V
+ _ 0-20 V
Fig. 2 (a) forward biased zener diode
0
ID mA
V V
Fig. 2(b) Reverse biased zener diode
OBSERVATION TABLE: • Draw the characteristic curve of zener diode (V-I) for both forward and reverse bias and plot them on the graph paper. S.NO
Forward Bias Current(mA) Voltage(zener)
Reverse Bias Voltage(zener) Current(mA)
1
0.40
1
2
0.50
2
3
0.60
5
4
0.65
7
5
0.70
7.5
6
0.75
7.55
7
0.80
7.85
REVIEW QUESTIONS: 1. 2. 3. 4. 5.
What is a voltage regulator? What is the difference between a rectifier and zener diode? Define Avalanche and zener breakdowns. What is the behavior of zener diodes in forward bias? What are the applications of zener diodes other than regulation?
FINAL CHECK LIST: • •
Clean your equipment/materials and workbenches before you leave Return all equipment and materials to their proper storage area.
2
Zener diode
BS P-III
Model Measurements S.NO
Forward Bias Current(mA) Voltage(zener)
Reverse Bias Voltage(zener) Current(mA)
1
0.40
0
1
0
2
0.50
0
2
0
3
0.60
0
5
0
4
0.65
0
7
0
5
0.70
4
7.5
11
6
0.75
12
7.55
42
7
0.80
50
7.58
50
BS P-III
Institute of Physics
Reverse Characteristics of zener Diode Objects of the experiment To familiar with reverse characteristics of zener diodes. To become familiar with zener diode operation as a regulator
Introduction The Zener diode is a silicon p-n junction device that differs from rectifier diodes because it is designed for operation in the reverse breakdown region. It is known that when a diode reaches reverse breakdown, its voltage remains almost constant even though the current changes drastically. The symbol for Zener diode is given in fig 1, Thus, Zener diode is extensively used as voltage regulator in power supply circuits. A Zener regulator is an electronic device that maintains an essentially constant output voitage for a range of input voitage.
Figure: 1 Zener Breakdown : Two types of reverse breakdown in a Zener diode are avalanche and Zener. The avalanche breakdown occurs in both rectifier and Zener diodes at a sufficiently high reverse voltage due to the multiplication of the conduction electrons. The Zener breakdown occurs in a Zener diode at low reverse voltages. As Zener diode is heavily doped, the depletion region is very thin. As a result near the Zener breakdown voltage the field within the depletion region is intense enough to pull electrons from their valence bands and create current. Zener diodes with breakdown voltages of less than approximately 5V operate predominately in Zener breakdown. Those with breakdown voltages greater than 5V operate in avalanche breakdown. Characteristics: The rectifier only operates in forward bias condition, while the Zener diode works in both forward and reverse bias. In forward bias, Zener diode acts same as' the rectifier diode. In reverse bias, Zener diode limits the current until the breakdown voltage is attained. After the breakdown voltage, the device enters the region of constant voltage, i.e. the voltage drop across the Zener diode is essentially constant but the current through the device increases drastically.
EQUIPMENT & COMPONENTS EQUIPMENT: ■ Power supply (0-20V) COMPONENTS: • DMM (Digital multimeter) • Few connecting hard wires
• • • •
1
A bread board 100 Ohms resistor Zener diode ( 7.5V) Milli-Ammeter (0-50mA)
Zener diode
BS P-III
PROCEDURE: 1. Make the connections according to fig 2(a). In this case the Zener diode is forward biased. Tabulate the different values of voltages and current. 2. Rearrange the circuit as in fig 2 (b). Again take different readings of current through the ioad at different values of voltage across Zener diode. Observe the voltage drop across Zener diode at different input voltages.
0
+
mA
+ + _ 0-20 V
ID
V V
+ _ 0-20 V
Fig. 2 (a) forward biased zener diode
0
ID mA
V V
Fig. 2(b) Reverse biased zener diode
OBSERVATION TABLE: • Draw the characteristic curve of zener diode (V-I) for both forward and reverse bias and plot them on the graph paper. S.NO
Forward Bias Current(mA) Voltage(zener)
Reverse Bias Voltage(zener) Current(mA)
1
0.40
1
2
0.50
2
3
0.60
5
4
0.65
7
5
0.70
7.5
6
0.75
7.55
7
0.80
7.85
REVIEW QUESTIONS: 1. 2. 3. 4. 5.
What is a voltage regulator? What is the difference between a rectifier and zener diode? Define Avalanche and zener breakdowns. What is the behavior of zener diodes in forward bias? What are the applications of zener diodes other than regulation?
FINAL CHECK LIST: • •
Clean your equipment/materials and workbenches before you leave Return all equipment and materials to their proper storage area.
2
Zener diode
BS P-III
Model Measurements S.NO
Forward Bias Current(mA) Voltage(zener)
Reverse Bias Voltage(zener) Current(mA)
1
0.40
0
1
0
2
0.50
0
2
0
3
0.60
0
5
0
4
0.65
0
7
0
5
0.70
4
7.5
11
6
0.75
12
7.55
42
7
0.80
50
7.58
50
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