A power amplifier

A power amplifier Introduction: A power amplifier is an electronic device that changes the magnitude of a signal. It is usually used to transfer high power to a low output load such as speakers where there load is about 8 ohms [1]. The relationship between the output and input is called the transfer function. An important aspect of the amplifier is the gain. The gain is the ratio between input and output whether this input is current, voltage or power. Therefore, the gain does not have a unit. The quality of the amplifier is determined by many aspects, which are gain, bandwidth, efficiency, linearity, noise and others. As one of these characteristics increase the others may decrease. Therefore, the amplifier will be designed to meet the required specifications determined by the application for which it will be used for. The various designs of the amplifiers are classified into many types which include A,B,C,D and some other types derived by combining the basic ones such as class AB which is obtained from class A and class B pertaining to their efficiency and linearity [1]. Ideally, power amplifiers are supposed to deliver 100% of the power to the load. However, as some of the power dissipates in the components of the amplifier, hence we do not have ideal power amplifiers. It is found that the linearity has an inverse relationship to the efficiency of the amplifier. The classes A, B and C power amplifiers are considered inefficient but linear whereas the other types are considered efficient but more complex than the basic types. Class A power amplifiers are least efficient than the others. The efficiency of class B is much higher than class A, however, class C has the highest efficiency level compared to class A and B [2]. The scope of this paper is to discuss class B power amplifier in details. Class B power amplifier: This class of amplifier was developed in order to improve class A power amplifiers, which have low efficiency rating. [1-3] shows and explains the internal design, the efficiency, the advantages and disadvantages, and the applications of class B power amplifiers. Internal circuit and operation: To get a sufficiently good amplification of the input waveform in the output, a push-pull class B power amplifier configuration must be used. This configuration is based on two transistors. The term push-pull comes from the fact that two transistors in a class B amplifier conduct in alternating half-cycles of the input [1]. Moreover, there are two types of push-pull configurations, one with transformers and one without transformers [2]. A balanced centre tapped input transformer is used to split the incoming waveform signal into two equal cycles that are 180 degrees out of phase with each other. Another center-tapped output transformer is used to recombine the signals. If the transformer is ideal we can get two collector currents that flow in opposite directions, hence no magnetization of the transformer core takes place which in turn minimizes the distortion in between the two signals. Both transistors used are of NPN transistor type where their emitter terminals are connected together [2]. discusses the mechanism in which the circuit works. Primarily, when no input signal is present, both transistors are biased at cutoff. When a signal is present during the positive half cycle, the transistors base inputs are in anti-phase to each other which causes transistor TR1to become biased above cutoff due to the positive base input that drives a large collector current, while TR2 is still biased at cutoff as the base current will go negative, making the collector current decrease by an equal amount of the increase in the collector current in TR1. This will result in an amplified positive-output half cycle. When the input signal is in the negative half cycle, the same procedure is done but in opposite, resulting in TR1 returning to the cutoff state while TR2 start building until it becomes biased above cutoff. This will result in an amplified negative-output half cycle. The half cycles combine to produce an output amplified 360 degrees signal with distortion. This effect is the push-pull effect. Advantages and Disadvantages of Class B power amplifier: Class B amplifiers have an advantage over class A amplifiers which is that the collector current is zero when the input signal to amplifier is zero that cause no power dissipation in the quiescent condition which leads to higher efficiency [1]. The main goal of using power amplifiers is to generate maximum AC power to the load, while consuming the minimum DC power possible from the supply. The efficiency of class B amplifiers in all types may reach up to 75% which is much higher than class A amplifiers [2]. The equation shown above is used to calculate the percentage efficiency of all power amplifiers. Pout is the power delivered to the load and PDC is the power taken from the supply. Class B amplifiers has one main disadvantage which is the high distortion that occurs in the output signal. This type of distortion is called the crossover distortion [2]. This distortion occurs when the transistors are switching over from one to another. Each transistor requires minimum voltage VBE which is about 0.7V to conduct. When one transistor is turning off by having VBE less than 0.7V and the other transistor is turning on but still the input voltage is not greater than VBE, the resulting is a zero voltage â€Å"flat spot† on the output wave shape as it crosses over from one half of the waveform to the other [2, 3].According to [2], the crossover distortion cause a reduction in the overall peak to peak value of the output waveform causing the maximum power output to be reduced. Hence, class B power amplifiers today are not used in many applications; it is only used as an audio amplifier. There are many ways to get rid of crossover distortion effect, but the most commo n one is to bias both the transistors at a point slightly above their cut-off point [1, 2]. This will lead us to class AB Amplifier circuit which is out of this paper scope. Application: The cost of class B amplifier is not high; therefore it is used in low budget designs. Furthermore, it is used in designs where the quality of the sound is not important because of the distortion it provides [3]. However, class B amplifier is preferred in designing audio power amplifiers [3]. [3] reveals that most of the time the music will be low so the signal will act as if it is in class A region. This means that the distortion will not be that bad. Moreover, the distortion can be minimized by using a negative feedback loop [3]. [3] also emphasizes that the sound power produced by this amplifier is huge and it can be run without heat sinks. Conclusion: This research was conducted in order to investigate the properties of class B power amplifier. First an overview about power amplifiers was considered in order to develop a better understanding about the reasons behind classifying them to many types. It was found that each class has its own application which it suits for. This is determined according to many aspects such as linearity and efficiency which are inversely proportional. Class B was found to be higher in efficiency compared to class A but less in linearity. Looking into the configuration of class B, it was found that class B amplifier has two possible configurations, one with a transformer and the other without the transformer. Both configurations works with two transistors where each one conducts for a half cycle (180 degrees), which gives the opportunity to the other transistor to cool. However, the configuration where the amplifier does not have a transformer is more efficient because less energy is lost in elements as a result of eliminating the transformer core. Class B amplifier was found to be used in low cost designs and designs where the clarity of the voice is not important. The crossover distortion can be removed by using a negative feedback loop or bias both transistors at a point slightly above their cut-off point, which is the idea of class AB power amplifier.

What I Most Appreicate About My Grandmother

S. Day GENENG 103-201 April 5, 2012 5 paragraph essay Everyone has something in their life that they appreciate, for instance their mom, family, kids or their job. Whatever the case be, always appreciate the better things in life. So always keep a good mind setting and a positive attitude. There are a lot of things that people fail to realize that are most appreciative. What I most appreciate about my grandmother is how much she entertains, motivates and supports her family. At times my granny can be entertaining to me. She loves to tell stories to us about how she grew up in the south.She also has a temper so sometimes when someone says or does something she doesn’t like she will snap out on them. It’s only funny to me when I’m not the one getting grilled. In addition, to that she will sit and lecture anybody about whatever, so don’t do or say anything that will set her off. When she gets to talking it is too late to turn around and walk away because she will go on and on about it until she proves her point. Regardless of her snapping and lectures granny can be a loving and caring person. She loves church and is in the choir on Sundays.Everyone at her church loves to her sing solo, so she walks around the house and practicing her songs. I love how entertaining she can be, so anyone in need of some entertainment just comes to grannies house its always live. As kind-hearted as my granny is, she also has the quality of being a motivator. Throughout my life she always motivated me to do well in school and pushed me to be the best I can be. She always told me to â€Å"Leave those boys alone and get your education!! †. Even though I didn’t listen, I still kept that in mind and still received my diploma and now enrolled in college.I love it when she tells everyone at her church how proud she is of me. She lets everyone know that I made the Dean’s list while I was in high school. However, I believe that when she is gone , I’m going to be the one that motivates everyone in the family, because my granny has taught me a lot and made me the smart, beautiful young lady that I am today. I know deep down inside she wants all her grandchildren to be successful in life. Even though she doesn’t tell us, she wants to proud of all of us since her children are all grown up.From the love and the care of my granny, to the helping hand that will remain grateful, and the motivation she gives me, I truly love Canzinetta Webb and believe she is one of the best things that ever happen to me. My family and my granny are equally important to me but my granny is like the back bone of our family. Although I’m her grandchild she took me into her home as if I was her own. For this reason, I love her so much, because she didn’t want to see me go into foster care. She works hard to provide for me and my family. There’s always food on the table and clothes on our backs.Obviously, my granny is the back bone of our family because every Sunday my granny cooks a big dinner and all my family comes to our house to eat. I love Sundays because that’s when I get to see my other family I haven’t seen in a while. So when everyone leaves they will be leaving with a smile and a full stomach, maybe even a plate to-go. Yet, she supports her family however, whenever help is needed she is always been there for whoever family or not. For example, my aunt was a short a couple hundred dollars on her light bill, my granny was willing to help her pay the rest so her lights wouldn’t be off.Clearly my granny plays a big role in our family, she is a wonderful person and anyone would begin to love her once they got to know her. There are a lot of things that people fail to realize that are most appreciative. Appreciating your life is about being grateful for the people that are in your life that make it better, and the things that you have, even if they may not be everything in which you may desire. We must be able to prefer to appreciate the things we cannot have instead of trying to appreciate things that we would not be able to appreciate.

Retail Report on Coach Inc Report

Coach Inc. designs, produces and markets a prestigious line of handbags, briefcases, wallets and wristlets, shoes for men and women, jewelry, apparel and accessories. They also offer tops for women. Their products are majorly leather based. The company has been one of the best handlers of leather brands in the United States of America for a very long period of time. They have an extensive overseas marketing strategy and have in the recent years explored markets abroad. It has sold sturdy leather purses in unchanging traditional classic styles for a very long period of time. Coach Inc. has partnered with some companies for the acquisition of different licenses. The companies include: Movado for watches which is a global license, Jimlar for footwear which is only available in the US and Marchon for eyewear available worldwide. Their target market cuts across all divides. For a long time, the company has been targeting the female but the trend has changed of late whereby their new market target is the males. The main aim for this shift is to change the image and reposition the company as a full range accessory maker and not just handbag manufacturer. This was a very good strategy and provided about 40% of the company’s sales. Coach achieved this by openning an only men store in New York City. The company’s major sales are derived from direct-to-consumer channels. The company’s global market is also their new target market. This is attributed to the fact that they are carrying out an extensive global marketing programme which is aimed at boosting their sales globally. Several stores have also been opened outside the United States in order to capture the overseas market. The basic strategy for the expansion is to add the number of products that bear the name Coach and the number of customers buying these products. Coach has been spending a lot of time doing market research to carefully identify their main customer target. A lot of resources has been spent carrying out international research which has given them a positive result. They have an approach that is customer oriented and has enabled the organization to mount hands-on response to the recent economic downturn. Coach Inc’s major competitors are Dooney and Bourke, Kate Spade, Gucci, Prada, Wilsons the leather Experts, Kenneth Cole, Hermes, Jones Apparel, Liz Claiborne and Polo Ralph. The major companies here are either owned privately or by other European conglomerates manufacturing leather luxury brands. Other competitors include: Louis owned by LVMH Moet Hennessy and Fendi owned by Gucci group. Another group offering competition here are the leather manufacturing companies which tend to imitate what Coach Inc is producing. Examples of such companies are Ann Taylor and Laura Leather Goods which imitated the Coach Inc’s products and had to pay for the damages caused. I am very optimist that Coach Inc. will succeed because they have a good strategy to reach all corners of its market. This is evident just from the types of items that they manufacture and just from the powerful brand name that they posses in the leather industry. Â  Their products are carefully designed so that almost every age group can get a taste of the products produced here.

Three Dreams in Wide Sargasso Sea - 2449 Words

Outline Thesis statement: the interpretation of the content of the three dreams and the analysis of the function of them in Wide Sargasso Sea. I. Introduction The three dreams of Antoinette, the heroine in Wide Sargasso Sea, serve as a significant role throughout the novel. This essay aims at interpreting the context of the three dreams and analyzing the function of them. II. Body: A. the interpretation of the underlying content of the three dreams 1. The theory of symbolism 2. Dream I presented the symbol â€Å"forest† and this dream reflected a signal of danger. 3. Dream II presented the symbol â€Å"white dress†, â€Å"tree†, â€Å"enclosed garden† and this dream showed the future of her marriage. 4. Dream III presented the†¦show more content†¦Helen Tiffin commented on the functions of mirror in Rhys’s works, â€Å"†¦Rhys’s heroine relies on mirrors and mirror images, they are central to Rhys’s depiction of her dilemma, unable to find their own worth†¦ † (Helen Tiffin 329) Antoinette last saw her reflection in this dream, â€Å"†¦I saw her—the ghost. The woman with streaming hair. She was surrounded by a gilt frame but I knew her.† (Jean Rhys 154) Years of imprisoned life deformed her image and deprived of her identity, therefore, she could not figure out herself i n the looking glass and took what she saw as a ghost, which is a mark of a complete breakdown in her recognition of her own identity. Tia emerged in her third dream too, standing by the pool at Coulibri, her homeland, and beckoning to her. The pool of water serves as a looking glass and reflects her image in West Indies. Water is penetrable, not like the glass that is hard, cold and preventing her uniting with her reflection. Therefore, if she jumped into the pool, she would regain her black and Creole identity in West Indies. However, she had another choice since an â€Å"English† identity was also beckoning to her â€Å"†¦and the man who hated me was calling too, Bertha! Bertha!† (Jean Rhys 155) Finally, she made up her mind to jump into the pool and tear up her present identity â€Å"Bertha† instead of coming back to the man who robbedShow MoreRelatedJane Eyre vs Wide Sargasso Sea Essay example1635 Words   |  7 Pagesï » ¿Tyler Perimenis Professor Mathews English 2301W 21 October 2014 Symbolism through Theme Of Jane Eyre and Wide Sargasso Sea â€Å"To produce a mighty book, you must choose a mighty theme. No great and enduring volume can ever be written on the flea, though many there be that have tried it,† stated Herman Melville. 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