lab 3- Christian Andrade

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City College University of New York Department of Electrical Engineering EE 32200 Saurabh Sachdeva Laboratory Report #3 Regulated DC Power Supply Christian Andrade Due date: 11/03/2022 Semester: Fall 2022

Regulated DC Power Supply Introduction Almost all basic household electronic circuits need an unregulated AC to be converted to constant DC, in order to operate the electronic device. All devices will have a certain power supply limit and the electronic circuits inside these devices must be able to supply a constant DC voltage within this limit. Therefore, a DC power supply is practically converted to each and every electronic system. Objectives The student will design a regulated power supply, which will meet or exceed the specifications listed below: OUTPUT VOLTAGE RANGE = 0 - 12 VDC MAXIMUM OUTPUT CURRENT (IMAX) = 200 mA PEAK TO PEAK RIPPLE (at 200Ma output current) < 25 mV LOAD REGULATION < 1% Percent load regulation is defined as: Vout ( at Imin ) – Vout ( at Imax ) ¿ ¿ Vout ( at Imin ) Characteristics of Regulated DC Power Supply The most common DC power supply is consisted from a combination of a transformer, rectifier, filter, and regulator. A basic diagram is shown below: Figure 1: A block diagram of a regulated DC power supply

Figure 2: A structure of a transformer Transformer A transformer is an electrical device used to convert AC power at a certain voltage level to AC power at a different voltage, but at the same frequency. The construction of a transformer includes a ferromagnetic core around which multiple coils, or windings, of wire are wrapped. The input line connects to the 'primary' coil, while the output lines connect to a 'secondary' coil. The alternating current in the primary coil induces an alternating magnetic flux that 'flows' around the ferromagnetic core, changing direction during each electrical cycle. The alternating flux in the core in turn induces an alternating current in each of the secondary coils. The voltage at each of the secondary coils is directly related to the primary voltage by the turns ratio, or the number of turns in the primary coil divided by the number turns in the secondary coil. Rectifier A rectifier is a circuit that is used for converting AC supply into unidirectional DC supply. This process of converting AC to direct current DC is also called as rectification. These bridge rectifiers are available in different packages as modules ranging from few amperes to several hundred amperes. Mostly in bridge rectifier circuits, semiconductor diode is used for converting AC since it allows the current flow in one direction only. Figure 3: A diodes rectifier

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Vin (red) is our line signal, and after the diodes bridge, the Vout signal is rectified (blue) Filter After the diodes bridge, a capacitor and a resistor are used to smooth (filter) the output after rectification so that a nearly constant DC voltage is supplied to the load. The pulsating output of the rectifiers has an average DC value and an AC portion that is called ripple voltage. The filter capacitor reduces the amount of ripple voltage to a level that is acceptable. A resistor and an inductor can be combined with the capacitors to form filter networks. In a filter circuit the capacitor is charged to the peak of the rectified input voltage during every positive portion. Between the portions, the capacitor begins to discharge until the next portion is there. The rate of discharge is determined by the RC time constant formed by the capacitor and the resistor. Regulator A Zener diode provides the constant 6v reference voltage to the positive input of the op-amp. A voltage divider composed by a 10k potentiometer provides an adjustment of the output voltage suitable for the op-amp. Then, the op-amp drives a BJT that function as a “buffer”. R1 & R2 are feedback resistors that limit our Vout to 12V. Since the op-amp has limited output current, a transistor will be connected to Vout in order to maintain higher current than the op-amp. Figure 5: Shunt Zener and an Op-Amp voltage regulator Figure 1: Vout after the RC filter

Prelab i. Find the value of R that about 10mA flows through the Zener diode: The unregulated voltage enters through the resistor and hits the Zener diode. The result is Vout = Vz = 6v @ 10mA. ii. Find the value for R1 and R2 so that the output voltage ranges from 0-12v: Since the Vin = V(+) = 6v, we need a gain of 2 in order to get Vout = 12v. Therefore R2 = R1, and in our experiment we decided to use the 6k resistors. R1 = R2 = 6K Figure 7: Full voltage regulator Figure 2: Shunt Zener (part of the voltage regulator) R = Vin ( unregulated ) − Vz I = 16.97 − 6 10 = 1.1 kΩ

iii. Simulation of the following circuit (no regulator): One time with load current of 0A, and the second time with load current of 200mA. Vout of I L = 0 mA is 18.56v, and when I L = 200 mA Vout is 15.47v LOAD REGULATION = Vout ( at Imin ) – Vout ( at Imax ) Vout ( at Imin ) = ¿ ¿ 18.56 v – 15.47 v 18.56 v = 16.64% iv. Simulation of the complete power supply with regulator: Figure 8: A circuit for the simulation of the filter capacitor Figure 9: Simulation of the unregulated voltage with 0mA and 200mA load current

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Calculation of R4 & R5 for Vout = 6v: Since the current through the Zener is 10mA, this current is also flowing throw R4 & R5. Our potentiometer is 10k and for a value of 6v: R5 = 6K Ω and R4 = 10K-6K = 4K Ω The graphs in figures 11 and 12 show that our regulator is operational and stable at 0mA and 100mA. Laboratory Figure 10: The full regulated DC Supply (0-12v) with a load of 100mA R4 R5 100mA Figure 11: Simulation of the regulated & unregulated voltage at output current of 1mA Figure 12: Simulation of the regulated & unregulated voltage at output current of 100mA

In this part we had to construct the Regulated DC power supply, as it is on figure 10. The load current will be constructed from resistor that will consume current. One test will be with Vin = 6v, and the second test will be with Vin = 12v. Results i. Vin = 6v: Load Current (mA) Vout (V) Vripple (mV) 0 6.0000 6 40 5.9948 6.5 80 5.9903 8 120 5.9832 11 160 5.9799 18 200 5.9763 24 V ( ¿¿¿ = 6 v )= Vout ( at Imin ) – Vout ( at Imax ) Vout ( at Imin ) = 6 v – 5.9763 v 6 v = 0.395% LOAD REGULATION ¿ ii. Vin = 12v: Load Current (mA) Vout (V) Vripple (mV) 0 12.0000 6.5 40 11.9950 7 80 11.9910 9 120 11.9870 12.5 160 11.9779 17 200 11.9656 25

V ( ¿¿¿ = 6 v )= Vout ( at Imin ) – Vout ( at Imax ) Vout ( at Imin ) = 12 v – 11.9656 v 12 v = 0.287% LOAD REGULATION ¿ Conclusions This experiment is very important for Electrical Engineers. Every digital and electronic system nowadays has this component, and we think that it’s a fundamental thing to know how to design and build such a system. The circuits that were tested in this lab are: the shunt zener, the voltage regulator, and the complete regulated power supply. These circuits were first designed and implemented in MultiSim where we could check if our system works or not. We have learned that as long as the output current increases, the ripple voltage increases as well. Since the output current is increasing, it’s getting harder for the system to maintain it at a given fixed voltage, and this is why we see that the Vout is decreasing a little when the output current is increasing. Figure 16: Vout vs Current load (12v) Figure 17: Ripple Voltage vs Current load (6v)

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