Rectification circuit for a dc power supply

Rectification circuit for a dc power supply 1. Introduction Most of the electronic devices do not power on AC basis, and if so it will conduct a lot of power and will be damaged the first moment it operates. Thus a device that reduces the voltage and correspondingly smoothes the output voltage to become much more stable and reliable to use than the AC which is the DC is needed. A question may arise that asks why do not use batteries to supply a DC voltage. Well, it is a good it a good question, but batteries are expensive and does not handle large electronic devices. Imagine having a desktop on batteries and having to change its battery every half an hour or so, it is a nightmare. As a result, in this case, a linier DC power supply that operates from fixed (ex: at home) AC voltage is needed. A rectification circuit do all that automatically. It smoothes and filters the current and make it a better than a battery DC source. The report paper will focus primarily on the technical aspects of the Rectification circuit used in the linear DC power supply. Other aspects than mentioned will not be included. 2. Discussion 2.1. Linear power supply AnACpowered linear power supply usually uses atransformerto convert the voltage from the wall outlet (mains) to a different, usually a lower voltage. If it is used to produceDC, arectifieris used. A capacitoris used to smooth the pulsating current from the rectifier. Some small periodic deviations from smooth direct current will remain, which is known asripple (Wiki, 2009). The voltage produced by an unregulated power supply will vary depending on the load and on variations in the AC supply voltage. For critical electronics applications alinear regulatorwill be used to stabilize and adjust the voltage. This regulator will also greatly reduce the ripple and noise in the output direct current. Linear regulators often provide current limiting, protecting the power supply and attached circuit from over current (Wiki, 2009). Figure 1 illustrates two common linear power supply circuits in current use. Both circuits employ full-wave rectification to reduce ripple voltage to capacitor C1. The bridge rectifier circuit has a simple transformer but current must flow through two diodes. The centre-tapped configuration is preferred for low output voltages since there is just on diode voltage drop. For 5V and 12V outputs, Schottky barrier diodes are commonly used since they have lower voltage drops than equivalently rated ultra-fast types, which further increase power conversion efficiency. However, each diode must withstand twice the reverse voltage that a diode sees in a full-wave bridge for the same input voltage. The linear voltage regulator behaves as a variable resistance between the input and the output as it provides the precise output voltage. One of the limitations to the efficiency of this circuit is due to the fact that the linear device must drop the difference in voltage between the input and output. Consequently the power dissipated by the linear device isVi-VoÃÆ'- Io. While these supplies have many desirable characteristics, such as simplicity, low output ripple, excellent line and load regulation, fast response time to load or line changes and low EMI, they suffer from low efficiency and occupy large volumes. Switching power supplies are becoming popular because they offer better solutions to these problems (National, 2002). 2.2. Transformer Atransformeris a device, figure 2, that transferselectrical energyfrom onecircuitto another throughinductively coupledconductorsà ¢Ãƒ ¢Ã¢â‚¬Å¡Ã‚ ¬the transformers coils. A varyingcurrentin the first orprimarywinding creates a varyingmagnetic fluxin the transformers core, and thus a varyingmagnetic fieldthrough the secondarywinding. This varying magnetic fieldinducesa varyingelectromotive force (EMF)or voltage in the secondary winding. This effect is called mutual induction. If aloadis connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (VS) is in proportion to the primary voltage (VP), and is given by the ratio of the number of turns in the secondary (NS) to the number of turns in the primary (NP) as follows: Step down transformers convert electrical voltage from one level or phase configuration usually down to a lower level. They can include features for electrical isolation, power distribution, and control and instrumentation applications. Step down transformers typically rely on the principle of magnetic induction between coils to convert voltage and/or current levels. Step down transformers are made from two or more coils of insulated wire wound around a core made of iron. When voltage is applied to one coil (frequently called the primary or input) it magnetizes the iron core, which induces a voltage in the other coil, (frequently called the secondary or output). The turns ratio of the two sets of windings determines the amount of voltage transformation. An example of this would be: 100 turns on the primary and 50 turns on the secondary, a ratio of 2 to 1. Step down transformers can be considered nothing more than a voltage ratio device. With step down transformers the voltage ratio between primary and secondary will mirror the turns ratio (except for single phase smaller than 1 KVA which have compensated secondarys). A practical application of this 2 to 1 turns ratio would be a 480 to 240 voltage step down. Note that if the input were 440 volts then the output would be 220 volts. The ratio between input and output voltage will stay constant. Transformers should not be operated at voltages higher than the nameplate rating, but may be operated at lower voltages than rated. Because of this it is possible to do some non-standard applications using standard transformers. Single phase step down transformers 1 kva and larger may also be reverse connected to step-down or step-up voltages. (Note: single phase step up or step down transformers sized less than 1 KVA should not be reverse connected because the secondary windings have additional turns to overcome a voltage drop when the load is applied. If reverse connected, the output voltage will be less than desired). 2.3. Rectifier Arectifieris an electrical device that convertsalternating current(AC) todirect current(DC), a process known asrectification. Rectifiers have many uses including as components of power suppliesand asdetectorsofradiosignals. Rectifiers may be made ofsolid statediodes,vacuum tubediodes,mercury arc valves, and other components (Wiki, Rectifier, 2009). While half-wave and full-wave rectification suffice to deliver a form of DC output, neither produces constant-voltage DC. In order to produce steady DC from a rectified AC supply, a smoothing circuit orfilter,is required. In its simplest form this can be just areservoir capacitoror smoothing capacitor, placed at the DC output of the rectifier. There will still remain an amount of ACripplevoltage where the voltage is not completely smoothed. Sizing of the capacitor represents a trade-off. For a given load, a larger capacitor will reduce ripple but will cost more and will create higher peak currents in the transformer secondary and in the supply feeding it. In extreme cases where many rectifiers are loaded onto a power distribution circuit, it may prove difficult for the power distribution authority to maintain a correctly shaped sinusoidal voltage curve (Wiki, Rectifier, 2009). For a given tolerable ripple the required capacitor size is proportional to the load current and inversely proportional to the supply frequency and the number of output peaks of the rectifier per input cycle (National, 2002). The load current and the supply frequency are generally outside the control of the designer of the rectifier system but the number of peaks per input cycle can be affected by the choice of rectifier design. A half-wave rectifier will only give one peak per cycle and for this and other reasons is only used in very small power supplies. A full wave rectifier achieves two peaks per cycle and this is the best that can be done with single-phase input. For three-phase inputs a three-phase bridge will give six peaks per cycle and even higher numbers of peaks can be achieved by using transformer networks placed before the rectifier to convert to a higher phase order (Wiki, Rectifier, 2009). To further reduce this ripple, acapacitor-input filtercan be used. This complements the reservoir capacitor withinductor and a secondfilter capacitor, so that a steadier DC output can be obtained across the terminals of the filter capacitor. A more usual alternative to a filter, and essential if the DC load is very demanding of a smooth supply voltage, is to follow the reservoir capacitor with avoltage regulator. The reservoir capacitor needs to be large enough to prevent the troughs of the ripple getting below the voltage the DC is being regulated to. The regulator serves both to remove the last of the ripple and to deal with variations in supply and load characteristics. It would be possible to use a smaller reservoir capacitor (these can be large on high-current power supplies) and then apply some filtering as well as the regulator, but this is not a common strategy. The extreme of this approach is to dispense with the reservoir capacitor altogether and put the rectified waveform straight into a choke-input filter. The advantage of this circuit is that the current waveform is smoother and consequently the rectifier no longer has to deal with the current as a large current pulse, but instead the current delivery is spr ead over the entire cycle. The downside is that the voltage output is much lower approximately the average of an AC half-cycle rather than the peak. 2.4. Regulator The regulator is an electrical regulator designed to automatically maintain 3. The Proposed Circuit * The proposed circuit shall have an input voltage equals to 220v. * A centre-tapped step down transformer with 220v output and 12v output. * 2 diodes (1N4001) working independently (note: duel regulated) as half-wave rectifiers. * 2 capacitors (1000u) to smooth the signal. * 2 voltage regulators (LM7815C) to regulate the coming voltages from the capacitors. * 2 small values capacitor (10u) for final smoothing for the output voltage. * The output voltage of 0-5v. 4. Conclusion One of the best ways to output an efficient and reliable DC power supply is to use linear power supply, which uses a step-down transformer, a rectification circuit, a regulator and a filter. The step-down transformer takes the voltage down from 220v to 12v, then the rectification circuit smoothes and filters it using capacitors and diodes, as a result, the output DC voltage would be 0-5v with a minimal ripple factor using the proposed circuit as mentioned. Works Cited National, S. C. (2002, September 1). Introduction to Power Supplies. Santa Clara, California, USA. Wiki. (2009, December 10). Power supply. Retrieved December 14, 2009, from Wikipedia, the free encyclopedia: http://en.wikipedia.org/wiki/Power_supply Wiki. (2009, December 9). Rectifier. Retrieved December 16, 2009, from Wikipedia, the free encyclopedia: http://en.wikipedia.org/wiki/Rectifier Power supply. Retrieved December 15, 2009, from: http://www.kpsec.freeuk.com/powersup.htm http://www.allaboutcircuits.com/vol_3/chpt_3/4.html Wiki. (2009, December 12). Rectifier. Retrieved December 15, 2009, from Wikipedia, the free encyclopedia: http://en.wikipedia.org/wiki/Voltage_regulator AC to DC Cuircts. Retrieved December 16, 2009, from: http://www.discovercircuits.com/DJ-Circuits/acdc1.htm Power supply. Retrieved December 15, 2009, from: http://www.trcelectronics.com/power-supply.shtml Step-down transformers. Retrieved December 14, 2009, from: http://www.powertransformer.us/stepdowntransformers.htm Step Down Transformers. Retrieved December 15, 2009, from: http://www.electricityforum.com/electrical-transformers/step-down-transformers.html

Fashion in 20 Years

Erika Annalisa Sagh 2MEI 20 years of change? The over abundance in brands, the constant development for new products and the continual demand for innovation in style, will certainly remain relevant in 20 years as much as it does today. Fashion will develop quickly in the fields of production development and undoubtedly work forward instead of reliving the passed. However, the most intriguing changes in the fashion world within the next 20 years will be noticeable in the domains of manufacturing and sustainable revitalization of products and how they will connect.In application of the current European crisis it is clear that people are becoming more conscious of where there money is being spent and how they can possibly save more wisely. The morality behind the importance of helping and supporting your own economy will forever remain, though whether it will be practiced may technically be but a theory. Western cultures will continue to seek cheap manufacturing alternatives in second a nd third world countries, because it offers the possibility to over-produce and support the fast fashion addiction.As the evolution in economy triggers a direct growth within the field of manufacturing, the everlasting demand for innovating and luxurious goods will incline as well. These points all aid in allowing actual consumption within the coming years to multiply from its current state. If the future predicts to experience a noticeable growth of consumers, rising to approximately 1. 8 billion, it would be of no surprise that more brands will emerge and companies will be looking into producing their garments and products more quickly to feed the demand.The demand will undoubtedly create an abundance of opportunities for the fashion industry, as developments in style, textile and processing will be forced to transpire. However, as a state for humanity these so called windows of opportunities will possibly not create revolutionary changes. Accounting China’s current regress ion in foreign manufacturing demand, a shift from this current fashion driven country to another developing country may occur.The demand from western-based countries to China is slowly diminishing based mainly upon the fact that quoted prices have elevated beyond comfort. Though China is beginning to manage their organizations better, it raises some issues of whether western demand will remain located or as previously mentioned, shift. China does expect their economy to grow within the upcoming years, however this growth may account solely for domestic demand. In order to continually be apart of the fashion realm, China may have to keep their prices low or have the government interfere.More of the Chinese population is gradually becoming less interested to work in factories, while more comfortable positions within a store or hotel are sought after. In short, as the country grows away from the communistic regime the people will desire a much more comfortable lifestyle away from poor conditions and factory work. Now it is not to say that the manufacturers in other upcoming worlds wont be categorized as sustainable. It’s a known fact that the fashion industry is classified as one of the most polluting industries in the world, and much more focus is now being spent on how to change this.From the amount of fertilizer used in cultivating cotton to the abundant quantity of chemicals exhausted in processing plants, it is evident that the creation of fashion is drastically aiding in the progression of global warming. Though due to the size of the industry, any small changes such as the conservation of fresh water or the protection of environmental status would help. Eva Kruse, Chairman of the Nordic Fashion Association has already begun gathering support from celebrities and international designers to discuss sustainable options.With already 1000 people aboard, their long-term goal is to eventually declare sustainability as a worldwide fashion value. Though they aspire to soon take part in united nation conferences and create a code of conduct for the industry, the possibility of eliminating cheap manufacturing is nearly impossible. It is not saying that if the sector reacts to aspects of this code that it will not create a great impact, but that redesign, reuse and recycle will take precedence over fair wages. Clothing will be designed using biodegradable materials such as bamboo, milk or recyclable plastics and polyester.Clothing will no longer be apart of landmass and the environment itself will be considered more green and clean. However as stated, the use of these materials is undoubtedly more expensive to produce and manufacture into garments. Sustainable machinery will become more expensive to buy and maintain, while health codes, which will be implied, will also account for a raised budget. Since it will be the big companies, which will drive the demand they will be able to influence the consumers to agree with sustainability but p erhaps not price.Prices can fluctuate gradually, however the public will never agree to pay ridiculously high amounts. As fast-fashion will not fade within the near future, people will still demand new seasons and more collection in order to satisfy their materialistic and trendy needs. Companies will have to agree in saving money through cheaper labour and not expect all products to be produced closer to home. Countries such as India, Bangladesh and Cambodia will most likely become visited terrain for production instead of China, whereas the likeliness of African labour is more questionable due to the unstable status of the government and disruption.In conclusion, there are many solutions available in creating a more sustainable fashion industry, however these solutions may be quicker to realize than the issue of fair trade itself. I believe that people are not ready to give up their addiction to buying, and fast fashion is not just a trend but also a new way of life. The idea of m inimalistic buying will have to develop slowly within society, it may visible in 50 years but 20 years seems too soon. The categorized second world countries such as China are progressively becoming first world and it is unsurprising that their production price quotes are higher than before.I believe that if the fashion industry takes a strong shift towards sustainability that affordable manufacturing in second and third world countries will be sought out, to balance and maintain â€Å"cheaper† ticketed prices. In the future, the world may look different because certain countries, which are currently related directly to fashion, may disappear or even change their status, while new countries will appear in order to realize this sustainable aspiration. First step, be kind and save the planet we live on. Second step, find a way to live in a fair trade world.

A Brief History of a Colony That Never Was

New Devon colony was founded on the north-west coast of the modern USA in the Delaware river’s valley.  Ã‚   It was the Indians who had lived here before Europeans came. These were the Indians who spoke the language of Algonquian group. They called themselves Lenni Lenape that meant ‘progenitors‘ or ‘first people’.Other Indian tribes called them ‘grandfathers’ and this fact also confirms that Lenni Lenape was the oldest tribe in this valley. The Indians hunted, fished, farmed cultivating cereals and legumes.   Depending on the season the Indians migrated from forests to the coast. At the beginning of 17th century about seven thousand people lived here.First European investigators of these lands were Dutch. However some seafarers investigated the North-West coast earlier: Englishman John Cabot (1497), Frenchman Giovanni da Verrazano (1524), Spaniard Estevan Gomez (1525), Frenchman Jehan Allefonsce (1542), Englishman Sir John Hawkins (15 62) and others.In 1615 Dutch Johan Stuyvesant left his country for the north-west coast to find suitable place for trading. In June being not far from New Foundland the ship unfortunately took fire. Stuyvesant had to land in order to repair the ship. After the examination of this place the captain became sure that lands are favorable for trade furriery and the river was full of fish.As a result of   Stuyvesant voyage the Dutch post Hoek was founded here.   Soon Englishmen learnt about these lands. They were very impressed with stories about fertile valley and in 1632 John Welsh visited this territory. He was enthusiastic about the prospects of these lands and confirmed everything   the Dutch traders had told.So in 1635 the territory of New Devon was granted to the Earl of Worcester and Englishmen began to immigrate here. Those Dutchmen who to swore fidelity to King could own the lands they had settled before. The land settlement in 17th   century required careful planning an d leading.It was very expensive and risky business. The settlers had to sale more than four thousand miles, they needed food, arm, clothes, seed, implements. Only small group of rich immigrants could afford to pay for such voyage. Others used special colonization agencies. These organization paid for the trip while settlers were bound to work off this debt in the colony as   servants. After four – five years servants could even get a plot to farm.The relationship between the Indians and settlers of New Devon were not so troubled as we can think. William Penn and his Society of Friends or Quakers living in neighboring Pennsylvania influenced the situation greatly. To follow them New Devon concluded a treaty with the Indians in 1701 to keep the peace.As for   economics of New Devon it prospered. The main business was agriculture. Many people however became employed as small fish processing or milling plants workers. Shipbuilding flourished. Cereals, wood, dairy products wer e exported to the southern colonies., West India and Europe.Too busy with commerce residents of New Devon didn’t pay much attention to the education and were obviously behind the southern colonies in this field. Only by the middle of 18th century King’s College was opened here. In 1739 ‘New Devon Weekly Journal’ began published.When granted to the Earl of Worcester King also gave a charter to New Devon. This document proclaimed authority   to be exercised by so called freemen – free colonists. The result of it was that assemblies took over the control of finance. The governor appointed by the Earl couldn’t even collect taxes and spent budget money without assemblies permission. When in 1684 Britain attempted to reestablish King’s rule and cancel the charter colonists simply expelled the governor send by London.Though British authorities realized the necessity to rearrange the Empire the situation in America wasn’t favorable to do this. Colonies got accustomed to independence and required more freedom. To consolidate power Britain had to begin struggle. The first step was the Sugar Act passing in 1764.The sugar act put a tax on sugar, wine, coffee, silk that shipped to the colonies from countries other than Great Britain. New Devon traders combined efforts to   boycott English goods. Residents used only those products which were produced by New Devon plants. Later in 1764,Parliament enacted a Currency Act to prevent paper bills of credit issued in any of King's colonies from being made legal. Since the colony were a deficit trade area and were constantly short of hard currency, this measure added a serious burden to the colonial economy.Equally objectionable from the colonial viewpoint was the Quartering Act, passed in 1765, which required colonies to provide royal troops with provisions and barracks.   But the act that angered the residents most of all was The Stamp Act. The Stamp Act put a tax on al l printed paper goods that colonists bought. Colonists had to pay a tax when buying books, newspapers and playing cards. A person who finished college had to pay a tax on the diploma.Lawyers had to pay a tax on the wills, agreements and other documents. To show that the tax had been paid, a stamp seller put a stamp on the paper.   The hostility arose. People caught officials collected taxes and tarred them. In October of 1765 in response to   Massachusetts assembly New Devon send delegates in New York to discuss the Stamp Act. After the long disputes   the congress enacted to consider as legal only the taxes imposed by colonies themselves. However George III was not going to make any concession. The Revolution became inevitable.During the Revolution many nearly 7000 men of New Devon enlisted for service in spite of the fact that there no important battles here except several skirmishes. New Devon provided the Army with food and arm.Lack of ammunition made residents to melt the statue of King to cast bullets. In 1781 English army surrendered to American and French ones. On September 3, 1783 Great Britain signed Treaty of Paris –   the peace settlement proclaimed the independence, freedom and sovereignty of the colonies. New Devon as well as other colonies became independent.Bibliography1.  Ã‚  Ã‚  Ã‚  Ã‚   About Connecticut; 15 July 2004; available from htpp://www.ct.gov./ctportal/cwp/view.asp?a=843&q=246434; Internet2.  Ã‚  Ã‚  Ã‚  Ã‚   Boorstin, Daniel J.   The Americans: Vol. 1: The Colonial Experience, Vol. 2: The Democratic Experience, Vol. 3: The National Experience, Hardback ed., Random House, 19753.  Ã‚  Ã‚  Ã‚  Ã‚   Dugan, Jeannine Colonial Immigration: An Overview; 25 January 2004; available from htpp://www.suite101.com/article.cfm/5871/32260; Internet4.  Ã‚  Ã‚  Ã‚  Ã‚   Morris, Richard B.; Henry Steel and Jeffrey B. Morris, eds. Encyclopedia of American History, 6th ed., Hardback ed., Harper & Row, 19825.  Ã‚  Ã‚  Ã‚  Ã‚   Pennsylvania state history,   available from htpp://www.phmc.state.pa.us/bah/pahist/overview.asp?secid=31; Internet6.  Ã‚  Ã‚  Ã‚  Ã‚   State of Delaware (A brief history), 12 July 2004; available from htpp://www.state.de.us./gic/facts/history/delhist.htm; Internet

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