A power amplifier

A supply amplifierIntroductionA power amplifier is an electronic device that changes the magnitude of a charge. It is usually utilize to transfer eminent power to a low railroad siding accuse such as speakers where there load is about 8 ohms 1. The kin between the output and stimulant is called the transfer function. An important aspect of the amplifier is the gain. The gain is the ratio between introduce and output whether this input is genuine, voltage or power. Therefore, the gain does non have a unit. The quality of the amplifier is determined by many an(prenominal) aspects, which argon gain, bandwidth, cleverness, linearity, noise and opposites. As whiz of these characteristics increase the others may decrease. Therefore, the amplifier pull up stakes be designed to meet the required specifications determined by the application for which it will be employ for.The various designs of the amplifiers are branchified into many types which hold A,B,C,D and some othe r types derived by combining the basic integritys such as mob AB which is obtained from curriculum A and class B pertaining to their skill 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 comp superstarnts of the amplifier, wherefore we do not have persuasionl 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 in cost- opinionive except linear whereas the other types are considered efficient but more daedal than the basic types. path A power amplifiers are least efficient than the others. The efficiency of class B is more higher than class A, however, class C has the highest efficiency level compared to class A and B 2. The compass of this paper is to discuss class B power amplifier in details.Class B power amplifierThis class of amplifier was developed in raise to repair class A power amplifiers, which have low efficiency rating. 1-3 shows and explains the intrinsic design, the efficiency, the goods and outrages, and the applications of class B power amplifiers.Internal rophy and operationTo view a sufficiently good amplification of the input undulation shape in the output, a push-pull class B power amplifier descriptor must be used. This mannequin is based on both junction transistors. The term push-pull comes from the fact that two transistors in a class B amplifier conduct in alternate(a) 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 mannequin with each other. Another center-tapped output transformer is used to recombine the signals. If the transformer is ideal we basis accept two storage b attery currents that flow in opposite directions, hence no magnetization of the transformer core takes place which in turn minimizes the spin 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 circle works. Primarily, when no input signal is present, both transistors are diagonaled 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 in a higher place cutoff due to the positive base input that drives a greathearted collector current, small-arm 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 procedur e is make but in opposite, resulting in TR1 re crook 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 amplifierClass 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 employ power amplifiers is to generate maximum AC power to the load, while overwhelming 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 address the percentage efficiency of all power amplifiers. Pout i s 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 cross 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 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 general peak to peak value of the output waveform causing the maximum power output to be reduced. Hence, class B power amplifiers straight off are not used in many applications it is only used as an audio amplifier. There are many way s to get rid of crossover distortion effect, but the nearly common 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.ApplicationThe 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 pith that the distortion will not be that bad. Moreover, the distortion can be minimized by using a negative feedback loop 3. 3 as well as emphasizes that the sound power produced by this amplifier is huge and it can be incline without heat sinks.ConclusionThis research was conducted in order to investigate the properties of class B power amp lifier. 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 match to many aspects such as linearity and efficiency which are mutually 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 lo w cost designs and designs where the lucidness of the voice is not important. The crossover distortion can be remove 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.