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ISTANBUL TECHNICAL UNIVERSITY DEPARTMENT OF ELECTRICAL ENGINEERING POWER ELECTRONIC CIRCUITS FALL 2008, CRN: 11473 ASST. PROF. DENIZ YILDIRIM PROJECT REPORT MINIPROJECT I 15 V DC Adapter GROUP MEMBERS 040050348 040050441 040050410 Yunus Gündüz Ali Çağlıyan Ersin Köse Electronics Eng. Control Eng. Control Eng. SUBMISSION DATE: OCTOBER 23, 2008 Objective of Project The objective of this project is to design a standart household AC/DC adaptor which output must provide regulated 15 V DC at a load current of 0.5 A. To build this circuit, firstly circuit elements must be obtained, secondly value of circuit elements must be calculated. Step 1 : Choosing the elements of Circuit Up to the circuit diagram which has given before, elements of circuit are obtained and settled on the diagram which is drawing in Figure 1. Figure 1: Circuit diagram Above diagram was drawn in PSpice Circuit Analyze Program. In this figure all the components of circuit has drawn and ready for the analyze. The differences between the main project there are extra elements such as the switch witch make the regulator on/off easily by the user. The other extra element is the fuse tube which keeps the circuit over current dangers. Rest of the circuit element types is same as main project. Step 2 : Calculating the values of elements First of the circuit element is transformator which convert the voltage amplitude. This element has been chosen 15W 220V/24V. Although the LM7815C device needs 20V input value which is requirement of regulator and diodes, transformator has 24 V output voltage because this is a standard, cheep and easy findable. Beside of that the reason of choosing transformator as 15 W is provide the necessary power for load and the circuit elements needs. It is fact that this value is a little bit higher then circuit needs but the reason of choosing high capacity, transformator could be use any other project that might will be required more power than this device. Second of the circuit elements are diodes which are rectifying AC to DC. This element was chosen D1N4001 model. This diode type is useful to project needs. For example the forward voltage current (If) answer the circuit needs and forward voltage drop value is convenient for device. The other element of circuit is electrolytic capacity which is used for filtering. from the formula which is taken from course notes, ∆V=Vm/2fRC; C = Vm/ (2*f*R*∆V); R’s value is approximately 30ohm. (parallel regulator resistance is ignoring because it is much more bigger than 30 ohm) ∆V/Vm is should be less than 10%, f is 50Hz. Finally, minimum C value(ripple voltage=10%) is calculated as 1.1 mF so C is chosen 2.2 mF 25 V electrolytic capacity because it is one of the standard values and works properly with D1N4001 diode. It means when capacity charges, current do not warm diode. One of the other element of circuit are Blue Light Emitting Diode (LED) and Rled (R1).LED is chosen a standard Blue Led which has voltage current (If) is 20mA and forward voltage drop value 4V.So Rled value calculated as by using formula below, Vi- Vled= Rled* If, (Vi is regulator input voltage) So minimum value of Rled calculated as 900 ohm. However, Rled was chosen as 1.5k to use LED safely. One of the important element of circuit is regulator which makes output voltage as stabile in 15 V. Regulator was chosen LM7815c because this model is cheap, easy to find and its PSpice model is available on internet. There are also C1 and C2 capacitors using parallel to regulator for filtering the input and output of regulator voltage. As indicated in 78** datasheets (*) C1 equals 220nF and C2 equals 100nF. Process of the Adapter’s Building There are four stages between input and output voltage. Converting amplitude Rectifiying Filtering Regulating . ~220VAC 15 VDC By using 15 watt 220/24 transformator (TX1) amplitude of input voltage is decreasing to 24V. Then by using four D1N4001 (D1, D2, D3, D4) diodes as bridge 24 V Ac voltage is rectifying. After that up to parallel capacitor (C4) connected to the circuit for filtering so ripple voltage become less than 10%. Finally, rectified input voltage and current is stabled with regulator to make safe the DC output values in the regulating step. There is also fuse lamp was used to make circuit more safe (Cutting the circuit into less loads incident which occur wrong movements while experiment). Simulations and Results After calculating all values of components the circuit was settled in PSpice circuit analyze program (Figure 1 ) and observe below results. Figure 2: Red line shows regulator input voltage-Green line shows regulator output voltage As seem in the Figure 2 and Figure3 input voltage of regulator changes between 20.972V and 21.838V. Figure 3: Red line shows regulator input voltage-Green line shows regulator output voltage This shows that, ∆V/ Vm=0.886/21.838=3.96% <10% which is as like as expectations. Figure 4: Red line shows regulator input voltage-Green line shows regulator output voltage As seem in the Figure 4, curser shows the output of regulator voltage is 15.107 V which is the almost same value with intended before. Figure 5: AC current at the secondary side of transformer As shows in Figure 5, these current peaks shows capacity is charging. In other times since C4 voltage bigger than input voltage, capacity is discharging until these two voltage value become same. Results and Real Oscilloscope Prints of Circuit Load Current(A) No load 0.05 0.10 0.15 0.20 0.25 0.3 0.35 0.4 0.45 0.5 Regulator input current(A) 0,022 0,07 0,12 0,17 0,22 0,27 0,32 0,37 0,42 0,47 0,52 Pin(W) 2 3,7 5,4 7 8,4 10 11,5 13,2 14,8 16,4 17,5 Vcdc 32,75 32,13 31,40 30,74 29,94 29,15 28,32 27,43 26,72 25,80 25,00 Pdc (W) 0,72 2,25 Pout (W) 0 0,75 1,5 5,23 2,25 6,58 3 7,87 3,75 9,06 4,5 10,15 5,25 11,22 6 12,126 6,75 13 7,5 Table 1: Measurements Result Circuit is tried and saved the above results. Figure 6: Real regulator input voltage Pout/ Pin 0% 20,30% 27,80% 32,10% 35,70% 37,50% 49,10% 39,80% 40,50% 41% 42,85% Pout /Pdc 0% 33,30% 39,80% 43% 45,60% 47,60% 49,70% 51,70% 53,50% 55,70% 57,70% Figure 7: Real regulator output voltage As seem in the Figure 6 and Figure 7 oscilloscope prints shows that circuit is working properly. Prepared circuit has tested the load current values between 0 to 0.5A and Table 2 and Table 3 has drawn via Excel with this values. 70% 50% 40% Seri 1 30% 20% 10% 0.5 0.45 0.4 0.35 0.3 0.25 0.20 0.15 0.10 0.05 0% No load Pout/Pin 60% Load current (A) Table 2: Efficiency changing chart of Pout/Pi via Load current change 45% Load Current (A) 40% 35% 30% 25% Seri 1 20% 15% 10% 5% 0.5 0.45 0.4 0.35 0.3 0.25 0.20 0.15 0.10 0.05 No load 0% Pout/Pi Table 3: Efficiency changing chart of Pout/Pi via Load current change These 2 tables above are simply said that the efficiency of circuit is increasing by loading device because circuit is designed for 0.5 A. There is a fact that 47% efficiency is not a good value for a converter device and there is a mistake which causing by 15 W transformator. As mentioned before this device is expensive and experiment group maybe need this power later experiments. Also 25 V is capacitor value is not proper for the circuit. Reason of this mistake is before purchasing components group member calculated Capacitor’s output DC voltage as 25 V however, after the experiment in no load condition it seems that capacitor’s output DC voltage increase to 32 V. Consequently this high value harms capacity in long use condition (Capacitor’s heat increase and finally explode). Finally all the measurements were making with a device called avometre which includes Dc-Ac voltmeter, ammeter and also ohmmeter. Oscilloscope is used for observe the voltage’s characteristics where different nodes of the circuit. References D1N4001 type diode datasheet from the web page ‘www.alldatasheets.com’ LM7805c type regulator datasheet from the web page ‘www.alldatasheets.com’ All formulas which use for the calculations are taken from Asst. Prof. Deniz Yıldırım’s course notes.