Lab Report 1. Diode characteristics, Half Wave, Full Wave rectifiers

Analog Electronics Lesson 1. Characteristics of the Diode Lesson 2. Full Wave Rectifier Name: Sanzhar Askaruly ID: 201100549 Date: 17/09/2014 Introduction Diode is an electronic device having conductor at their ends. The principle behind the diode is similar to a valve or a gate, 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 be used 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 our theoretical 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 in oscilloscope. 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 Figure 1.1 and Figure 1.2 Figure 1.1 and Figure 1.2. Resistance test for forward and reverse bias diode 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 tasks were conducted only with germanium diode. The results of the measurement for germanium diode: Silicon Diode Forward bias BURNT Reverse bias BURNT Germanium Diode Forward bias Reverse bias 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 material without 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 high. 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. 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 V V I Vdiode Si Vdiode Ge 1 BURNT 0.242 2 BURNT 0.262 4 BURNT 0.277 7 BURNT 0.294 9 BURNT 0.304 The results of the measurement for germanium diode in the reverse bias: V mA V Idiode Si Idiode Ge 5 BURNT 0 10 BURNT 0 20 BURNT 0 Discussion & Analysis 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 are related 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 the following question: Q1. How does the diode behave as the supply voltage varies? Answer: b) in forward biasing the current is very low, until the voltage reaches a characteristic value for the diode, then it increases exponentially. In reverse biasing the current is extremely low, and is difficult 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. The principal schematic of circuit connection is illustrated below in the Figure 4. 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. Discussion & Analysis The graph originally shows the relationship between resistor voltage and germanium diode voltage. The diode 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 lets the 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 voltage across two series resistors, one of which was variable. The principal schematic of circuit connection is illustrated below in the Figure 4. Figure 5. Half-wave rectifier circuit with oscilloscope Obtained data Figure 6. Input voltage and output voltage graphs for half-wave rectifier Discussion & Analysis 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 notice that 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 lacks the negative half-wave, and the input one has slightly higher amplitude. Conclusion In this part of the laboratory, the principle of diode operation was practically understood. Initially its internal 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. The principal schematic of circuit connection is illustrated below in the Figure 4. 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 Discussion & Analysis 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 shape of input graph became more round. This is due to the fact that we have AC input voltage and no diodes try to rectify input. Task 2 Disconnecting: J16, J14 Discussion & Analysis 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 Disconnecting: J15, J16 Discussion & Analysis Disconnection of D4, D5 diodes lead to half rectified output voltage. Current is flowing only in one direction. Oscillograph shows both channels rectified. However, channel 1 sinusoid is pulsing during the negative half. Task 4 Disconnecting: J14, J17 Discussion & Analysis Disconnection of D3, D6 diodes also lead to half rectified output voltage. Current is flowing only in one direction. Oscillograph shows both channels rectified. However, channel 1 sinusoid is pulsing during the positive half. Q4. From the tests carried out, the operation of the Graetz bridge can be observed. Which of the following statements is true? Answer: e) None of the above is true Conclusion In this part of the laboratory, the operation of full rectifier was observed with the help of oscilloscope. By disconnecting sets of jumpers, we limited circuit to specific loops. Channel 1 and channel 2 voltages were recorded. However, the last two figures appear to be new for me, since I saw pulsing voltages in the input. I could not find explanation for that yet. However, I hope to find out the reason after submission of the laboratory report. Reference List Figure 1. Semiconductor diode. Retrieved 17/09/2014 from http://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/s1600/575pxMultimeter.png Figure 3. Voltage – Current characteristics of semiconductor diode. Retrieved 17/09/2014 from http://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%2 0Different%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%2 0Different%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