electronics lab 4 report bilive

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Apr 3, 2024

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1 Centennial College ELECTRICAL ENGINEERING TECHNICIAN Course: EET-129 Electronics 1 Name (Please Print ): Bilive khatri Jerry Huang Student Number: 301362967 301356189 Date: 2024/02/11 LAB #4 CAPACITOR INPUT FILTER OBJECTIVE: The student will be able to demonstrate: 1- The effects on the DC output voltage and ripple voltage when an electrolytic capacitor is used as a filter. 2- The effects of a variable load on the DC output and ripple voltages. THEORY: The periodic charging of the DC output above and below its average value is called ripple. Most electronic equipment requires smooth DC operating voltages. The output of a rectifier cannot be applied directly to such equipment because of the ripple. Therefore, the ripple must be reduced or smoothed. The circuits for doing this are called filter circuits. A- The filtering action of a capacitor is directly related to its capacitance and load resistance. B- A filter capacitor charges to the peak value of the rectified voltage. C- A filter capacitor discharges through the load resistance. D- The discharge time depends on the time constant (RC) of the load resistance and the filter capacitance. The ripple output of a rectifier supplies energy to the load in pulses. The ripple can be reduced if some of the energy from the source is stored while the rectifier is delivering a pulse. This stored energy can then be released to the load between supply pulses. This provides

2 energy for the load on a continuing basis and is the basic operating principle of a capacitance filter. A capacitance filter is simply an electrolytic capacitor connected across the rectifier output. The capacitor charges rapidly to the peak rectifier voltage as shown in Fig 1. Fig. 1 The rate at which the capacitor discharges, and therefore, the average level at which the output voltage is maintained, depends mainly on the RC time constant of the capacitor and the load resistance. The charge time is generally very fast because of the very low source resistance. Percent Ripple The purpose of the power supply filter is to smooth out the pulsating DC produced by the rectifier. There is a generally accepted figure of merit which tells how good the filter does its job. This figure of merit is called the percent ripple. The percent ripple is defined by the equation

3 When using this equation, the ripple in the output is assumed to be a sine wave. While it is not really a sine wave, the ripple does have a nearly symmetrical wave shape, so our equation gives fairly accurate results. Figure 2 shows the output of a rectifier-filter network. To compute the percent ripple of this waveform, first measure the peak-to-peak value of the ripple. The ripple voltage has a peak-to-peak value of: 80 V - 60 V = 20 V. Fig 2 Therefore, the peak value must be one-half of this value, or 10 V. We can calculate the rms value of the ripple voltage by multiplying the peak by 0.707:

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4 Now we can obtain the approximate average DC voltage by taking the value midway between the upper and lower values of the ripple. In the example shown, the average DC voltage is 70 volts. Therefore, the percent ripple is: The percent ripple can be made lower if a larger capacitor is used or if the value of the load resistance is increased. Since the load resistance is normally dictated by the circuit design, the amount of ripple is controlled by the value of the capacitor. When you know the characteristics needed in the power supply, you can determine the value of filter capacitor required. The general equation for a full-wave or bridge rectifier is Where:

5 Components needed: - One transformer, 120 V/ 12 V AC (10:1 ratio or around that value) - Capacitors (50V) : 1μF, 4.7μF, 47μF, 100μF, and 470 μF - 1N4004 (four) Silicon Diodes. - 1 k Ω - 100 Ω PROCEDURE : 1- Assemble the circuit shown in Fig. 3. Fig. 3 - Connect a voltmeter and an oscilloscope across R1 (1 k Ω) 2- By changing the value of C1, fill in the chart on Table 1 by measuring across R1 the DC voltage with the voltmeter and the peak-to-peak ripple voltage using the oscilloscope.

6 Note: To observe the peak-to-peak ripple voltage set the oscilloscope input to AC coupling, and adjust the vertical setting of the channel to obtain a large vertical deflection. C1 DC VOLTAGE Peak-to-peak Ripple Voltage 1μF 11.34V 16.40V 4.7μF 13.27V 9.76V 47μF 15.22V 1.52V 100μF 15.27V 880mV 470μF 15.32V Enter. 240mV Table 1 3- Replace resistor R1 with a 100 Ω value. 4- By changing the value of capacitance, fill in the chart of Table 2. C1 DC VOLTAGE Peak-to-peak Ripple Voltage 1μF 6.57V 10.8v 4.7μF 6.78V 10.32V 47μF 7.33V Enter. 4.48V

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7 100μF 7.43V 2.64V 470μF 7.48V Enter. 560mV Table 2. 5- By observing the ripple waveform in the oscilloscope, calculate the ripple frequency (use the values of R1= 1 kΩ and C1= 470 µF). Show your calculations below. Vp(out)=1.414*14=19.8V V(DC)=19.8-1.4=18.4V Vr=192mV R ipple frequency(fr)=Vdc/Vr*R*C=18.4/192m*1k*470µF=204Hz 6- Remove one of the diodes from the circuit of Fig. 3. Use the values of R1= 1 kΩ and C1= 470 µF. (open diode) Measure and record the DC voltage measured across R1 and the ripple frequency. V R1 = 13.41V Ripple frequency= 60Hz Explain in the box below why the above values differ from the original values of Table 1. When we remove the one diode in bridge rectifier it will be halfwave rectifier.so in half wave rectifier the output voltage is lesser by 0.7v i.e. 16.5V-0.7V which is nearly to the obtained value 15.1V. The frequency is 60 Hz because were getting only half cycle.

8 7- Reinsert the diode you removed in step 6 and remove the capacitor C1 (this is a simulation of an open capacitor). Calculate and measure the DC voltage across R1. Show your calculations in the box below, and assume the second approximation for your calculations. V R1 (calculated) = 12.6V V R1 (measured) = 11.11V VP=19.8V V (Dc) =Vp(out) =Vp(sec) I=Vdc/RL =19.8/1000 =19.8mA Vr=2Vp/pi =2*19.8 =12.6

9 Submission Your lab must be uploaded in the Assignment Folder -> Lab 4. Marks: Mark. /100 Conclusion: The conclusion summarizes important points of the laboratory work. You must analyze the examples to add emphasis to significant points. You must also include features and-or things you done/benefits of a particular procedure, instrument, component or circuit directly related to the experiment. In this lab we learned to filter out the Dc voltage using capacitors in different types of rectifiers. We were able to observe the ripple waveform or filtered wavefor , and we were familiar with the calculation. Also we understand the different between halfwave and full wave rectifiers.

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10 Marks: Mark. /30 Rubric-Grading: Criteria Max. Grade Punctuality 10 Mark. Following Procedure and Submission 100 Mark. Conclusion 30 Mark. Neatness, Spelling, Grammar and Sentence Structure 10 Mark. Total Mark. /150