The Purpose of a Regulated Power Supply and the System Inside It - Coursework Example

?THE PURPOSE OF A REGULATED POWER SUPPLY AND THE SYSTEM INSIDE IT Introduction The power supply is the most basic component of an electronic circuit. It is the heart of any electronic circuit, gadget or appliance system. Without it, no gadget or electronic system will function. In layman’s term, a power supply can be compared to a physical heart, the brain, or the blood of ‘something’ that moves. If the power supply malfunctions, all the rest within the gadget and appliance system are affected. With the advent of integrated circuits (ICs), the power supply has gone to many innovations and complications in systems and designs and even in uses. So what is a power supply? In the days before complicated ICs and complicated digital electronics, a simple power supply was composed of a transformer and a rectifier circuit. The transformer is where alternating current or AC voltage enters. AC voltage comes from the normal voltage from the electrical outlet at home. It carries with it alternating current and has to be transformed and rectified into direct current (DC) so that it can power up the electrical appliance. It has an input and an output. The output is the desired DC voltage for an electronic circuit which depends whether it is 6 volts or 12 volts or even higher. Since it is the heart and that it supplies the main lifeblood of an electronic system, it is easy to locate, and if one has become acquainted with it, easy to troubleshoot and repair. That is easy said than done, but in any electronic troubleshooting mastery of the block- and schematic diagrams and every detail of the circuitry will ensure a troubleshooting success. For electronic technicians and engineers, pinpointing the location of the power supply is as easy as troubleshooting itself. 1.1 Definition of terms 1.1.1 Transformer – A transformer is a devised used to transform voltages or current; the transformation is from higher voltage to smaller voltage (step-down transformer), or from smaller voltage to higher voltage (step-up voltage). Most electronic circuits in appliances and gadgets use step-down transformers. For example, if the power supply in our home is 220 volts or 110 volts, we are going to use a step down-transformer to transformer the higher voltage and current to 6 volts, 9 volts, or 12 volts, as the case maybe. 1.1.2 Alternating Current/Direct current (AC/DC) – The current that enters a transformer is known as alternating current (AC). This is a static current which do not respond to the needed direct current of an electronic circuit. Therefore, the AC current has to be transformed into a DC or direct current. The AC voltage/current comes from the utilities company that supplies our electrical needs at home. First, we have to compare the different types of current and be able to name the parts in it. As mentioned, there are two types of current – the alternating current and the direct current. The alternating current is not regulated – the sine waves are alternating, and this has to be rectified using a diode or diodes, with a capacitor and other filtering components, so that the circuit can produce an output of a DC current. After we have transformed the AC to DC, then we still have to regulate it to match the needed voltage and current that a particular electronic circuit needs. In our high-tech world nowadays, designs have eliminated the transformer and other analog circuits; instead, integrated (IC) circuits have replaced many of the components. 1.1.3 Rectifier Circuit A rectifier is a diode or a circuitry of diodes that transforms alternating current into direct current. In a simple rectifier circuit, a diode is coupled with a filter capacitor and load resister to complete the rectification process. This produces a half-wave and does not completely provide full rectification. 1.1.4 Regulator A regulator can be a transistor or an integrated circuit (IC). The purpose of a regulator is to provide a steady DC output. A well-regulated DC is needed in circuits to produce the needed output or purpose of that particular circuit. (Meade and Diffenderfer, 2003, p. 809) An alternating current that comes from the electrical outlet in our homes has a voltage of 110 volts or 220 volts. Electrical utilities provide 60 hertz frequency. This is the reason why we need a transformer. The 220/110 volts that we get from the electronic outlet or the supply that we get from the electrical utilities in our homes cannot supply our electronic circuits which need only a fraction of these voltages and currents. For example, a simple radio needs only 6 volts. Our television set needs 220/110 volts, but this has to be transformed into a regulated DC voltage. Suppose we have a radio receiver which needs a 6 volts power. We have to provide 6 volts DC power supply. We can make a simple DC power supply for this. DC voltage is what our electrical appliance needs. Figure 1 Block diagram of a simple power supply. The arrow represents the input-output flow of voltage and current. The input of the transformer is AC and its output goes to the rectifier. The output of the rectifier goes to the electronic appliance. 1.2 Types of Power Supply 1.2.1 Converter – a converter, by its name, converts AC voltage to DC voltage. As explained in the previous sections, the different kinds of rectifier circuits convert AC to DC. Types of Rectifier Circuits Half-wave rectifier – uses a single diode, and produces half-wave; it is the simplest rectifier, and most economical type of power supply. It still produces DC voltage but rectification is not enough for circuits that need regulated and full-wave DC. A half-wave rectifier employs a single diode, a capacitive filter, and load resistor. The principle behind the half-wave rectifier is that the AC source flows through the diode and the resistor. The electron flow is from the cathode of the diode to the anode, which is against the direction of the anode of the diode symbol. The diode conducts only on each ac alternation when its anode is positive with respect to the cathode. When this happens, the ac voltage is within the resistor. The diode cannot conduct when the diode is reversed biased. This is because the diode is negative “with respect to its cathode ... and when this happens, all of the ac voltage is found across the diode and virtually none across the load resistor” (Diffenderfer, 2005, p. 113). Center-tapped full-wave Rectifier – this type of rectifier makes use of two diodes and a center-tapped transformer. It is more advantageous than the halfwave because it can provide “output power to the load during both alternations of ac input” (Meade and Diffenderfer, 2003, p. 805). Figure 8 Full-wave center-tap rectifier with a center-tap transformer. Full-wave Bridge – This type of rectifier uses four diodes, arranged like a bridge, connected from end to end and “has the power delivering capability of full-wave rectifiers and does not require the use of a center-tapped power transformer”. (Meade and Diffenderfer, 2003, p. 805) IC Regulator LT 11070CT SOURCE: Power Supply Circuits Sourcebook, Volume 1, by Intellin Organization (2008, p. 13). Figure 7 Converter using IC Regulator LT11070CT. A converter converts AC voltage to pure DC voltage. The output here is exactly 12 volts, filtered by several filter capacitors. The AC voltage passes through two filter transformers. 1.2.2 Inverter An inverter is a type of power supply that converts or inverts DC to AC. Figure 8 Application of an Inverter SOURCE: Power supplies, switching regulators, inverters, and converters, by Irving M. Gottlieb (1994, p. 4) An inverter is used to light a lamp, from a battery source. In the second example, it is used to drive a motor, also using a battery source. 2. Circuit and Operation A more detailed diagram can be shown in the next figure. Figure 2 shows four sections in the block diagram of a power supply. We have added a regulator. There is an AC input of, for example, 220/110 volts which flows to the transformer. The transformer is a step-down transformer which transforms a large input to a smaller unit, which is 6 volts. The 6 volts AC current enters the rectifier circuit and transforms the AC current into DC current. The Regulator regulates the output 6 volts. Figure 3 Block diagram with ‘smoothing’. This a bit complicated where we added the ‘smoothing’ which is actually the filter section of the popular supply. The smoothing reduces ripple in the conversion of the AC to DC. The purpose of a rectifier circuit is to transform the AC voltage into DC voltage. This is done through the use of components such as rectifier diodes, capacitors and resistors. The Regulator may be in the form of a transistor, a transistor circuit, or integrated circuit (IC). Simple half-wave rectifier circuit A simple half-wave rectifier circuit is composed of a single diode with a capacitor. Figure 4 Schematic Diagram of a half-wave rectifier circuit. This shows how 6V AC is transformed into 6V DC by simple rectification. Current and voltage here are still unregulated. Regulated DC will be produced through the execution of a regulator transistor or regulator IC. The output will be transformed into a regulated DC once it enters the IC or transistor regulator. Figure 5 shows a half-wave rectifier. A simple power supply with a regulator transistor Figure 6 The regulator being used here is an NPN transistor (negative-positive-negative), but in most cases nowadays, integrated circuits are used as regulators. Figure 7 Circuit using bridge-type full-wave rectifier. SOURCE: Power Supply Circuits Sourcebook, by Intellin Organization (2008, p. 13). Figure 8: Full-wave Bridge Rectifier Circuit with a transistor regulator and Regulator IC. SOURCE: Power Supply Circuits, Available from: http://www.eskimo.com/~ddf/Schematics/PwrSupplies/PS_Test1.pdf (Accessed 4 April 2011). 2.1 Theories and Laws in Electronics Ohm’’ Law – in determining the values of a circuit, we use the Ohms Law, i.e. if we do not what know the values of the other components. For example, Ohms’ Law states the voltage is directly proportional to the current and the resistance, and is expressed in the equation, thus: E = IR Wherein: E = voltage I = current R = resistance Ohm’s Law is further simplified by using this formula: E IR The equation means that if we are looking for the voltage, we simply multiply the current I and the resistance R; if the resistance is the unknown, we divide the voltage E with the current I. Using Driver Transformers Transformers can be used as drivers. It is used between a voltage source and an output stage. This concept is applied in circuits and not in the basic power supply, and where we are talking of the inductance and reactance of a circuit. Transformers can be used in audio amplifiers. A good design transformer can provide complex wave forms. The secondary waveform is an ac waveform with perfect symmetry. Here, we are using a N-channel MOSFET. Impedance can be measured through the formula: Xc = 1 2?fC Where: Xc = the capacitive reactance in ohms f = the sine-wave frequency in hertz C = the capacitance in farads 2.2 Regulator IC 7815 Figure 5 Regulated Power Supply using Regulator IC 7815. SOURCE: Practical Electronics, by D. K. Nath (2001, p. 28) The regulator IC 7815 belongs to a family of three-pin ICs. These are simple ICs whose three terminals point to the input-ground-output. In this circuit, two diodes are used to produce a full-wave circuit. Rectification is done by the two diodes IN4007, and filtering is completed by C1. The output of the rectifier becomes the input of the IC 7815, and the regulated DC output is further filtered by C2. The entire circuit has a common ground, termed in the circuit as the Common Rail (CR). 3. Conclusion The power supply is the most important part of an electronic circuit. Without it, the circuit cannot function; subsequently, the electronic appliance or gadget will not function too. In troubleshooting, it is important to know the different components and their functions in a schematic and block diagram. Mastery of the components is necessary and a must. The output of a power supply is known as direct current (DC), but it is not enough current to supply a circuit. The output DC voltage has to be regulated (by another circuit or IC) before it becomes a power source. Regulators come in various types but the present trend is the use of regulator ICs, which are more compact and smaller. The invention of nanotechnology has allowed electronic components to become smaller and smaller; thus we see gadgets which are tiny enough to be carried and used. The invention of the laptop and computers has been made possible with the application of ICs or microcomputers. All these components and circuits need power supplies or voltage inputs in order to become running and operational. References Diffenderfer, R., 2005. Electronic devices: systems and applications. United States of America: Thomas Delmar Learning. Intellin Organization, 2008. Power Supply Circuits Sourcebook, Volume 1. United States of America: Rikee Lloyd Group LLC. Meade, R. and Diffenderfer, R., 2003. Foundations of electronics, circuits and devices. United States of America: Delmar Learning. Nath, D., 2001. Practical electronics. India: Academic Publishers. Power Supply Circuits (n.d.). Available from: http://www.eskimo.com/~ddf/Schematics/PwrSupplies/PS_Test1.pdf [Accessed 4 April 2011 The Electronics Club, 2010. Power Supplies. Available from: http://www.kpsec.freeuk.com/powersup.htm [Accessed 5 April 2011]. Read More