Lab # 006 - Best lab report PDF

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31/09/2019

Lab Title :To obtain the V-I characteristics of Zener diode.

Objective :To study and verify the Voltage-Current relation in Zener Diodes by applying a voltage across it and measuring the corresponding current flowing through it.

Introduction Of Theory:Zener Diodes: Zener diode is a silicon semiconductor device that permits current to flow in either a forward or reverse direction. The diode consists of a special, heavily doped p-n junction, designed to conduct in the reverse direction when a certain specified voltage is reached..

Fig # 01

An ideal P-N Junction diode does not conduct in reverse biased condition. A Zener diode Conducts excellently even in reverse biased condition. These diodes operate at a precise Value of voltage called break down voltage. A Zener diode when forward biased behaves like an ordinary P-N junction diode. A Zener diode when reverse biased can either undergo avalanche break down or zener break down.

Avalanche break down:If both p-side and n-side of the diode are lightly doped, depletion region at the junction widens. Application of a very large electric field at the junction may rupture covalent bonding between electrons. Such rupture leads to the generation of a large number of charge carriers resulting in avalanche multiplication.

Zener breaks down:If both p-side and n-side of the diode are heavily doped, depletion region at the junction reduces. Application of even a small voltage at the junction ruptures covalent bonding and generates large number of charge carriers. Such sudden increase in the number of charge carriers results in Zener mechanism.

Forward bias Condition: 1|Pa ge

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The P-N junction supports uni-directional current flow. If +ve terminal of the input supply is connected to anode (P-side) and –ve terminal of the input supply is connected the cathode. Then diode is said to be forward biased.

Fig # 02

Reverse bias condition: If negative terminal of the input supply is connected to anode (pside) and –ve terminal of the input supply is connected to cathode (n-side) then the diode is said to be reverse biased.

Fig # 03

Cut in voltage of a diode: It permits current to flow in the forward direction as normal, but will also allow it to flow in the reverse direction when the voltage is above a certain value - the breakdown voltage known as the Zener voltage. The Zener diode specially made to have a reverse voltage breakdown at a specific voltage. If the output waveform tries to exceed the 7.5V limit, the zener diode will “clipoff” the excess voltage from the input producing a waveform with a flat top still keeping the output constant at +7.5V. Note that in the forward bias condition a zener diode is still a diode and when the AC waveform output goes negative

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Fig # 04

Circuit Diagram :-

Fig # 05

Practical Work :3|Pa ge

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Equipment :    

Resistor DMM Zener Diode Connecting Wires Breadboard

Procedure :Forward Bias Condition: 1. Connect the circuit as shown in Fig.1(PN Junction zener diode with milli

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.

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ammeter in series with the diode). 2. Initially vary Regulated Power Supply (RPS) voltage Vs in steps of 3 V. 3. Tabulate different forward currents obtained for different forward voltages. 4. Plot the V-I characteristics and calculate the resistance levels .

Reverse Bias Condition: 1. Connect the circuit as shown in Fig.2 .

2. Vary Vs in the Regulated Power Supply (RPS) gradually in steps of 3V. 3. Tabulate different reverse currents obtained for different reverse voltages. 4. Plot the V-I characteristics and calculate the resistance levels .

Tabular & Graphical Data :Forward Bias Condition: Using Zener diode of 3V Table # 01 Sr. No. 1 2 3 4 5 6 7 8 9 10 11

Vin

(V)

Vd

(V) 0 0.747 0.773 0.787 0.797 0.805 0.811 0.816 0.822 0.824 0.825

0 3 6 9 12 15 18 21 25 27 30

Id

(mA)

0 1.55 3.57 5.55 7.52 9.59 11.64 13.82 15.78 17.89 20.1

Reverse Bias Condition: Using Zener diode of 12V Table # 02 Sr. No. 1 2 3 4|Pa ge

Vin (V) 0 3 6

Vd

(V)

0 2.93 5.91

Id

(mA)

0 0 0 26961

4 5 6 7 8 9 10 11

9 12 15 18 21 25 27 30

8.92 11.30 11.37 11.45 11.54 11.57 11.66 11.74

0 0.5 2.39 4.36 6.35 8.41 10.31 12.37

Graph

Discussion of Results :   

The precautions are quite similar to that taken in a normal diode i.e Excessive flow of current may damage the diode Current for sufficiently long time may change the characteristics Zener diodes are used in voltage regulation in circuits because even when, A large current flows through, their voltage does not change appreciably.

Conclusion :The V-I characteristic of Zener diode indicates that characteristic of Zener diode in forward bias is same as PN junction diode. In reverse bias, a negligible constant current flow through the zener diode but the current becomes abruptly large at certain voltage. This voltage is called as zener voltage. This sudden and sharp increase in zener current is called as zener breakdown. 5|Pa ge

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This experiment is about to investigate the behavior of ZENER diode and analysis how it work. By observing the behavior of zener diode on different applied voltages and find the results and calculation for its practical proves.

References :

http://datasheet.octopart.com/1N4007-Diotec-datasheet-118605333.pdf

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https://www.physics-and-radio-electronics.com/electronic-devices-and-circuits/semiconductordiodes/vicharacteristicsofdiode.html

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https://electric-shocks.com/forward-and-reverse-bias-of-diode-explained-by-v-i-characteristiccurves/



https://www.electronics-tutorials.ws/blog/i-v-characteristic-curves.html



https://www.quora.com/What-is-the-cut-in-voltage-of-a-diode

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