Lab Report 1. Diode Characteristics Half

8/18/2019 Lab Report 1. Diode Characteristics Half

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Analog Electronics

Lesson 1. Characteristics of the Diode Lesson 2. Full Wave Rectifier

Name: Sanzhar Askaruly

ID: 201100549

Date: 17/09/2014


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Introduction

Diode is an electronic device having conductor at their ends. The principle behind the diode is similar to a valve or agate, which lets electricity flow only in one direction (Simple English Wikipedia, Diode). Application of diodes is

broad. They serve as converter from alternating current to direct current, met at the power supplies. Also they can beused in radio equipment to decode amplitude modulation. Nowadays, there are two basic semiconductor materials

which the diode is made from: silicon and germanium

Two types of semiconductors are joined to each other to produce semiconductor diode. One of them has spare holes( p side), and the other has extra electrons (n side). This results in the flow of electrons from the side, where there are

more electrons to the side where there are less of them, i.e. current. However, it is difficult to flow for the current in

the reverse direction. Connecting electrodes are following: positive p-side is anode, and negative n-side is cathode.

Figure 1. Semiconductor diode

Objectives

This laboratory work consists of two parts. In the first part of lab, there are tasks where we have to practically

understand the characteristics of semiconductor diode. Specifically, measure forward and reverse resistances,

voltages and the current. The measurements are to be collected into table. This will lead to strengthening ourtheoretical knowledge about the diodes. In the second part of lab, we deal with full wave rectifier, which is made of

four diodes. By removing jumpers, which disable diodes, we are to analyze the behavior of graph displayed inoscilloscope. Full wave rectifiers are vitally important to understand for us, since they play a key role in converting

alternating current into direct current.

Body

Lesson 1

Used equipment and electronic devices: Module MCM3/EV, Power supply PSLC or PS1-PSU/EV, jumpers,

Fluke 115 True RMS Multimeter, built-in silicon and germanium diodes, built-in resistors, oscilloscope

Task 1.1

The initial task was to measure the forward and reverse resistance of silicon and germanium diodes. From

the theory, diodes have high resistance whilst the reverse bias and low resistance when they are forward bias. The principal schematic of connection for taking resistance measurement is illustrated in the Figure1.1 and Figure 1.2

Figure 1.1 and Figure 1.2. Resistance test for forward and reverse bias diode


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To measure the resistance, multimeter was used, shown in the figure below.

Figure 2. Fluke 115 True RMS Multimeter

Obtained data

Initially, before starting we noticed that the built-in silicon diode of the MCM3/EV module was burnt. We

immediately let the teacher assistant know about that. With her permission, we continued lab. All the taskswere conducted only with germanium diode. The results of the measurement for germanium diode:

Silicon Diode Germanium Diode

Forward bias Reverse bias Forward bias Reverse bias

BURNT BURNT 0 kOhm 1.76 kOhm

Table 1. Forward bias and reverse bias resistances

Discussion & Analysis

As we can see from the table, germanium diode has no resistance when it is forward bias and high

resistance when it is reverse bias. This is because electrons flow from n-type material into p-type materialwithout any difficulty, however they face challenge when do the opposite. Based on this conclusion, it was

easy to guess the answer to the following question:

Q1. What are the difference between germanium and silicon diodes?

Answer: c) The two reverse resistances are hi gh.

Task 1.2

The aim of this task was to measure the voltage as a function of current during the forward bias, and the

current as a function of voltage during the reverse bias. First guess refreshed from theory is that voltage has

to increase if the current increases. However, we have to bear in mind, that in this case current flows from

anode to cathode. For the opposite, there is no current until breakdown voltage, i.e. reverse bias case. For

better explanation, graph below is provided.


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Figure 3. Voltage – Current characteristics of semiconductor diode

The principal schematic of circuit connection is illustrated below in the Figure 2.

Figure 4. Half wave rectifier circuit diagram

Obtained data (all tables with measured values, observed graphs and data, calculations):

All the tasks were conducted only with germanium diode. The results of the measurement for germanium

diode in the forward bias:

mA I 1 2 4 7 9

V Vdiode Si BURNT BURNT BURNT BURNT BURNT

V Vdiode Ge 0.242 0.262 0.277 0.294 0.304

The results of the measurement for germanium diode in the reverse bias:

V V 5 10 20

mA Idiode Si BURNT BURNT BURNT

Idiode Ge 0 0 0


Forward breakdown voltage after which current exponentially grows with voltage increase starts at about

0.15 V (Germanium diodes). As we can see from the table of germanium diode, its voltage and current arerelated with some function, not proportional. With the increase of current, the voltage increases and vice

versa. For the reverse bias case, there is no current flow. However, there is a theoretical breakdown voltage,approximately -100 volts, after which there is a reverse current flow, usually followed by diode burning

(Introductory Electronics Tutorial 4 –

Diodes). Based on these statements, we could guess the answer to thefollowing question:


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Q1. How does the diode behave as the supply voltage varies?

Answer: b) in forward biasing the current is very low, unti l the voltage reaches a

characteri stic value for the diode, then it i ncreases exponenti all y. In reverse biasing the

current is extremely low, and i s dif fi cult to measure.

Task 1.3

The objective of this task was to display the diode characteristics on the oscilloscope. Specifically, channel

1 probe was to measure the voltage across diode and channel 2 was used to test the voltage across the

resistor.


Figure 4. Oscilloscope connection into circuit

Obtained data

We achieved the resistance voltage over diode voltage, however forgot to record the camera shot onto phone.


The graph originally shows the relationship between resistor voltage and germanium diode voltage. Thediode does not let the current flow until breakdown voltage (open circuit). After breakdown voltage

(approximately 0.3 V) is reached, graph appears to be perpendicular. That means diode is opened and letsthe current flow through it. It becomes short circuit (constant voltage across it).

Task 1.4

The objective of this task was to analyze half-wave rectifier circuit behavior with the help of oscilloscope.Specifically, channel 1 probe was to measure the input voltage and channel 2 was used to test the voltageacross two series resistors, one of which was variable.


Figure 5. Half-wave rectifier circuit with oscilloscope


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Obtained data

Figure 6. Input voltage and output voltage graphs for half-wave rectifier


Channel 1 is represented by the yellow color, the input voltage. The channel 2 is represented by the blue

color, output voltage across series resistors. According to the figure obtained from oscilloscope, we noticethat input and output voltages are in phase, however the output voltage has its negative part rectified. This

is due to the diode property, which lets current flow only in one direction. Moreover, input voltage has

higher amplitude during positive half. In my understanding, this small voltage (difference) is needed to

switch the diode on (breakdown voltage). From Kirchoff`s Voltage Law for this diagram:

Vin = Vd + Vout

Vd = Vin - Vout

With these acknowledgements above, it is easier to answer the following question.

Q3. What are the differences in the 2 displayed signals?

Answer: d) The 2 signals are in phase, but the load signal l acks the negative half -wave,

and the input one has sli ghtly hi gher amplitude.

Conclusion

In this part of the laboratory, the principle of diode operation was practically understood. Initially itsinternal resistance, both forward and bias was observed, then by experimenting voltage and current change, the

relationship was defined. Finally, the behavior of half wave rectifier was analyzed with the help of oscilloscope. My

personal learning experience was developed as well. I learnt working with multimeter, MCM3/EV board, and

oscilloscope. These are the essential tools for future electrical engineer.

Lesson 2

Full Wave Rectifier (Graetz Bridge Rectifier)

The objective of this task was to analyze full-wave rectifier circuit behavior with the help of oscilloscope.

Specifically, channel 1 probe was to measure the voltage between anode of D3 and ground. Channel 2 was

used to test the output voltage across two series resistors, one of which was variable.


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Figure 7. Full-wave rectifier circuit with oscilloscope

Obtained data

The oscilloscope output when all the diodes are present. Channel 1 shows half rectification while the

channel 2 shows full rectification.

Task 1

Disconnecting: J14, J15, J16


Disconnection of three D3, D4, D5 leads to open circuit. No current flows through resistors. Hence,

oscillograph shows yellow input sinusoid on channel 1 and zero voltage on channel 2. Moreover, the shapeof input graph became more round. This is due to the fact that we have AC input voltage and no diodes tryto rectify input.


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Task 2

Disconnecting: J16, J14


Disconnection of D3, D5 diodes also lead to open circuit. No current flows through resistors. There is only

potential difference left of the input voltage. Hence, oscillograph shows yellow input sinusoid on channel 1

and zero voltage on channel 2. The shape of input graph is the similarly more round. This is also due to the

fact that we have AC input voltage and no diodes try to rectify input.

Task 3



Disconnection of D4, D5 diodes lead to half rectified output voltage. Current is flowing only in onedirection. Oscillograph shows both channels rectified. However, channel 1 sinusoid is pulsing during the

negative half.

Task 4



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Reference List

Figure 1. Semiconductor diode. Retrieved 17/09/2014 fromhttp://techpoem.com/wp-content/images/electronics/Reverse%20Biasing%20of%20P- N%20junction%20diode.jpg

Figure 1.1 and Figure 1.2. Resistance test for forward and reverse bias diode. Retrieved 17/09/2014 from

https://moodle.nu.edu.kz/pluginfile.php/109027/mod_resource/content/4/1.%20Diode%20characteristics%20and%2

0Different%20Circuits%20%28Updated%29.pdf

Figure 2. Fluke 115 True RMS Multimeter. Retrieved 17/09/2014 from

http://2.bp.blogspot.com/-iOx35Jz-xeE/Uzrj4uq50lI/AAAAAAAADuM/jP22mzkeNVQ/s1600/575px-Multimeter.png

Figure 3. Voltage – Current characteristics of semiconductor diode. Retrieved 17/09/2014 fromhttp://clivetec.0catch.com/imgs/ZenerDiagram.jpg

Figure 4. Half wave rectifier circuit diagram. Retrieved 17/09/2014 from

https://moodle.nu.edu.kz/pluginfile.php/109027/mod_resource/content/4/1.%20Diode%20characteristics%20and%2

0Different%20Circuits%20%28Updated%29.pdf

Figure 5. Half-wave rectifier circuit with oscilloscope. Retrieved 17/09/2014 from

https://moodle.nu.edu.kz/pluginfile.php/109027/mod_resource/content/4/1.%20Diode%20characteristics%20and%20Different%20Circuits%20%28Updated%29.pdf

Figure 6. Input voltage and output voltage graphs. Retrieved 17/09/2014 from personal archieve of the mobile phone.

Figure 7. Full-wave rectifier circuit with oscilloscope. Retrieved 17/09/2014 from

https://moodle.nu.edu.kz/pluginfile.php/109027/mod_resource/content/4/1.%20Diode%20characteristics%20and%20Different%20Circuits%20%28Updated%29.pdf

Germanium diodes. Retrieved 17/09/2014 from

http://www.learnabout-electronics.org/diodes_03.php

Introductory Electronics Tutorial 4 – Diodes. Retrieved 17/09/2014 from

http://www.antonine-education.co.uk/Pages/ELectronics_1/Electronic_Components/Diodes/intro_page_4.htm

Simple English Wikipedia, Diode. Retrieved 17/09/2014 from

http://simple.wikipedia.org/wiki/Diode
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Documents

Lab Report 1. Diode Characteristics Half