Dept. of Computer Science and Engineering

Transcription

1 Dept. of Computer Science and Engineering EECS 2210 Electronic Circuits and Devices Project Report Power Supply for a Mobile Charger Submitted by : Linda Chigbo Ariel Laboriante Ege Arslan Date 4/17/2015 The work in this report is our own. We have read and understood York University academic dishonesty policy and we did not violate the senate dishonesty policy in writing this report. Signature 1

2 Table of Contents 1.0 Introduction Purpose Project Scope Technical Section Constraints Initial Design Components Circuit Design Initial Design Second Design Final Design Analysis Testing Phase Phase 1: DC-Source (14 V) Phase 2: Power Outlet Source (110 V at 60 Hz) Conclusion References..14 List of Figures Figure 1: Pspice model of the first circuit design 5 Figure 2: Circuit diagram of the second design...6 Figure 3: Pspice model closely resembling the final design 8 Figure 4: Power supply project circuit assembled on the solderless breadboard 9 Figure 5: Testing the power supply project circuit Figure 6: Professor Mokhtar guiding us through the testing phase using the function generator.12 Figure 7: Function generator is unable to show voltage output due to the floating ground..13 List of Tables Table 1: Electrical components and the quantity used in the initial project design. 4 Table 2: Electrical components and the quantity used in the final project design

3 1.0 Introduction 1.1 Purpose The purpose of our design was to apply the knowledge we gained of electronic components from our EECS 2210 course into a project and create a device that has a real life application. Since phones have become a big part of daily life for many people, we decided to create a design which could be used to charge phones. 1.2 Project Scope Our project consists of designing and creating a DC power supply that will have a steady 5V output using electronic components to step down from a plug. Since we want to be able to use this as a supply for an android phone, our goal is to make not just the output voltage stable at 5V, but also the output current has to be at a stable 1.2A value. 2.0 Technical Section 2.1 Constraints Before creating the project circuit, our team carefully considered the constraints that limited the design of our circuit. First, we knew that we were working on limited time; therefore, we ruled out the option of ordering our components online since we knew it could take weeks for the order to arrive. Moreover, we were initially opting for a more compact circuit design (by using the bridge rectifier IC chip instead of the diodes for example), but due to limited parts and a limited budget, we modified our design so that our main objective of a steady 5V output would be met. 3

4 2.2 Initial Design Components Table 1: Electrical components and the quantity used in the initial project design Components Quantity Zener Diode 7805IC 1 Diode 1N Step down AC AC Converter ND 1 10 uf Capacitors uf Capacitors 3 10k Ω, 5k Ω, 1kΩ 1 of each 2.3 Circuit Design In the design phase, we had two iterations before we decided upon our final design. The detail of each iteration phase is discussed below Initial Design In the initial brainstorming phase, we thought about working off of the design that was provided in the laboratory instruction guide and then choose the components that would align with this model. We used a 12V voltage input at 60Hz, 4 1N4933 rectifying diodes, μ F capacitor, 1 10k Ω, and 1 1N5342B zener diode. The flaws of this model is that in order to be able to charge the mobile phone at a constant and stable voltage, we would require a voltage regulator to maintain stable voltage and a transformer to decrease the voltage to the desired value. The voltage after the bridge rectifier is about 11.3V, while that after the zener was about 0.8V which is incredibly low and is not suitable to charge a phone of any magnitude. One more thing was that the current was not up to 1.2A. This design did not meet our design goals, so we tried a different model. 4

5 Figure 1: Pspice model of the first circuit design Second Design In the creation of this model, we improved upon the mistakes we made from the previous model. To ensure that the output voltage and the output current meet the desired needs of our project scope, we implemented a design we found on the web. In the design of this model, we introduced the use of voltage regulator, to ensure stable output voltage. This model simply uses a bulk capacitor, several other small ones (100nF and 1 μ F), a LM7812 regulator, and transformer that has an output of about 14v 35v AC and an output current between 100mA to 1A. The schematic for this design can be seen below. 5

6 Figure 2: Circuit diagram of the second design In the course of implementing this design above, we had to keep in mind that we were constrained with limited parts and that the design above can only support a stable 12V output. The problem with this design is that we had no bulk capacitor to begin with, and the transformer that was available to us was of a 110 AC capacity. Secondly, with the capacitors we had, there was no way we could obtain the values we wanted, while maintaining safety at the same time. To fix this, we decided that we need to get equally large capacitors to match this, or we could try other alternatives. In the end, the consensus was that a new design would be ideal. 6

7 2.3.3 Final Design Table 2: Electrical components and the quantity used in the final project design Parts Used 1000uF capacitors 5 1N4933 Diodes 4 Quantity ND Transformer 1 10uF capacitors 2 LM7805(IC) regulator 1N5342B zener diode 10.5 Ω Power Resistor For this final design, we had to buy new capacitors with large magnitudes, as well as a power resistor, and a zener diode. We did some calculations to determine the value of the capacitors to use, as well as the value of the power resistor, while keeping in mind that we needed at least a 1.2A output current and a 5V output voltage. Steps for building this models is as follows; First, we connected the 4 diodes into the breadboard, then we connect the powers source. We found the voltage to be across the diodes to be about 13.79V. This voltage would be too high for the capacitors available to us, so we had to figure out a way to limit the voltage coming from the source in order keep the capacitors from burning out. From our observations and calculations, we knew that we had to connect a zener to regulate the voltage coming from the source. Using this idea, we connected a power resistor in series with the diodes, and then connected a 1N5342B zener diode to it. Now the measured voltage across the zener has reduced to approximately 7V. 7

8 Next, we connect the connected the uF capacitors in parallel and then measured the voltage again. We found the voltage to still be at about 6.99V. Then right after that, we connected the LM7805 regulator s input to the 5000uF capacitors and the output to the 2 10uF capacitors connected in parallel. Finally, we measured the voltage to be 5.02V and the current to be 1.15A. The final design picture as well as the schematics can be seen below. Figure 3: Pspice model closely resembling the final design In the above schematic, we did not have the PSPICE library part for the LM7805 regulator, so we put in its place the zener diode in D6 during the spice simulation. Also the resistor in R1 is a power resistor hence the small value. 8

9 Figure 4: Power supply project circuit assembled on the solderless breadboard 9

10 2.4 Analysis Before implementing our design, we made calculations in order to predict whether our circuit will have the output that we wanted. This analysis will also ensure that we will not destroy any components during the testing phase. The AC AC transformer converts the 110V AC voltage (60 Hz) from the power outlet into 14V AC. After the full wave rectifier, the voltage drops down to 12.6V. 14V 2(0.7V) = 12.6 V Before passing through the zener, we added a power resistor with R = 10.4 Ω to control the current: I = 12.6 V / 10.4 Ω = 1.2 A We needed the power resistor to ensure that the zener diode will not be damaged by a high amount of current. The power is calculated to be: P = I*V = 1.2(12.6) = 15W With P and R, we were able to choose the correct power resistor. The voltage drop across the zener diode is expected to be around 6.8V. Finally, the voltage regulator attached near the output will drop the voltage to 5V. The value of the capacitor was calculated based on the ripple voltage. The expected ripple voltage was 5V * (⅓) = 1.5V. Then solving to determine the value of the capacitor: Vr = 1/2fC, solving for C we get: C = 1 / 2*60*1.5V = = 5000 μ F 2.5 Testing Phase As mentioned in the Final Design section, we were not able to simulate the exact model of the circuit we wanted to build. Some parts that we planned to use were not in the PSPICE library. As seen in Figure 3, we were missing the LM7805 voltage regulator, the AC AC transformer and the power resistor. In order to ensure that we will not damage our electrical components, seeing as we have limited parts, we conducted two tests in order to see if our project design is correct. 10

11 2.5.1 Phase 1: DC-Source (14 V) During our first test, we used the DC power supply and removed the transformer from the circuit. By using the multimeter, we were able to measure the voltages across the input and output. We were not able to get an output initially due to incorrect connections in the full wave bridge rectifier. However, after correcting our mistake, we saw that the input voltage was limited to 8V by the zener diode. The voltage across the zener diode was 6.99 V which we expected. The capacitors limited the amount of current to 1.2 A. Finally, our output was 5V, which was just what we wanted to get. Figure 5: Testing the power supply project circuit 11

12 Figure 6: Professor Mokhtar guiding us through the testing phase using the function generator 12

13 2.5.2 Phase 2: Power Outlet Source (110 V at 60 Hz) During the second part of the testing phase, we connected our circuit to the 110 AC power source. We returned the AC AC transformer back to our circuit and plugged it in the outlet. At first, we hoped to see the output and the input voltages using the function generator. However, as seen in Figure 7, it was unable to show the correct waveform due to constraints with the floating ground in our circuit. Using the multimeter, we determined that our circuit was producing the correct output voltage of 5V. As expected, the voltage across the zener diode was around 7V and the input voltage was around 14V. Figure 7: Function generator is unable to show voltage output due to the floating ground 13

14 3.0 Conclusion During the course of this project, we learned that creating a DC power supply producing a steady voltage for charging phones involves a lot of constraints that need to be taken into consideration. First, the high voltage AC input from the power outlet must be converted into a small steady DC output. Second, the current must be limited so that it would not damage the phone since the internal resistance of the phone is made to be quite small in order to charge at a faster rate. Third, the electric components need to be as compact as possible in order for the convenience of travel. Our power supply was able to meet the first two objectives since we produced an output voltage of 5V with a current of 1.2A, similar to regular phone chargers. This project proved to be a great learning experience for us because with the freedom of being able to choose what to build, we were able to be more creative and use electrical components that we normally would not use in the EECS 2210 labs. We didn t have any major difficulties in this project other than finding the parts needed to build the circuit. We didn t know the part numbers so we were struggling with finding the parts with the right characteristics. Fortunately, we had some help from the TAs and they were able to suggest other methods of stepping down the voltage and controlling current. Moreover, it was fortunate that they were able to obtain most of the parts we needed for the project to work. Given the time and budget, we would like to improve this power supply project and make our circuit more compact. In the future, we would also like to improve the charging rate of the everyday phone charger. 4.0 References Aboelaze. YORK UNIVERSITY DEPT. OF COMPUTER SCIENCE AND ENGINEERING (n.d.): n. pag. Web. Plasmana. "Make a Simple 12 Volt Power Supply." Instructables.com. N.p., n.d. Web. 28 Mar