外文资料翻译及原文.doc

外文资料翻译及原文From：Switching Power Supply Design. Third Edition. McGraw-Hill.Using Power Semiconductors in Switched Mode TopologiesThe electric energy is not normally used in the form in which it was produced or distributed. Practically all electronic systems require some form of energy conversion. A device that transfers electric energy from a given source to a given load using electronic circuits is referred to as Power Supply.A typical application of a power supply unit (PSU) is convert utility AC voltage into regulated DC voltage required for electronic equipment. Nowadays in PSU the energy flow is controlled with semiconductors that are continuously switching on an off with high frequency. Such devices are referred to as switch mode power supplies or SMPS. They offer greater efficiency compared with linear supplies because a switch can control energy flow with low losses: when a switch is off, it blocks the flow of voltage and current, can be relatively low in both states. SMPS are also smaller in size and lighter in weight due to the reduced size of passive components and lower heat generation. The industry tended toward miniaturization, advancements in semiconductor technology, as well as various energy efficiency regulations have made switch the dominant type of PSR across practically the full spectrum of applications. Most of the switchers manufactured today for AC input applications include a PFC front end.Power supplies in the mid70s. We identified these as SWITCHMODE products. A switching power supply designed using ON Semiconductor components can rightfully be called a SWITCH MODE power supply or SMPS.In general, SMPS can be classified into four types according to the input and output waveforms:AC in, DC out: rectifier, off-line converter input stage DC in, DC out: voltage converter, or current converter, or DC to DC converter AC in, AC out: frequency changer, cycloconverter, transformer DC in, AC out: inverterFor many years the world of power supply design has seen a gradual movement away from the use of linear power supplies to the more practical switched mode power supply (S.M.P.S.). The linear power supply contains a mains transformer and a dissipative series regulator. This means the supply has extremely large and heavy 50/60 Hz transformers, and also very poor power conversion efficiencies, both serious drawbacks. Typical efficiencies of 30% are standard for a linear. This compares with efficiencies of between 70% and 80%, currently available using S.M.P.S. designs. Furthermore, by employing high switching frequencies, the sizes of the power transformer and associated filtering components in the S.M.P.S. are dramatically reduced in comparison to the linear. For example, an S.M.P.S. operating at 20 kHz produces a 4 times reduction in component size, and this increases to about 8 times at 100 kHz and above. This means an S.M.P.S. design can produce very compact and lightweight supplies. This is now an essential requirement for the majority of electronic systems. The supply must slot into an ever shrinking space left for it by electronic system designers.At the heart of the converter is the high frequency inverter section, where the input supply is chopped at very high frequencies (20 to200kHz using present technologies) then filtered and smoothed to produce dc outputs. The circuit configuration which determines how the power is transferred is called the TOPOLOGY of the S.M.P.S., and is an extremely important part of the design process. The topology consists of an arrangement of transformer, inductors, capacitors and power semiconductors.Regulation of the output to provide a stabilized DC supply is carried out by the control / feedback block. Generally, most S.M.P.S. systems operate on a fixed frequency pulse width modulation basis, where the duration of the on time of the drive to the power switch is varied on a cycle by cycle basis. This compensates for changes in the input supply and output load. The output voltage is compared to an accurate reference supply, and the error voltage produced by the comparator is used by dedicated control logic to terminate the drive pulse to the main power switch/switches at the correct instance. Correctly designed, this will provide a very stable AC output supply.In most applications, the S.M.P.S. topology contains a power transformer. This provides isolation, voltage scaling through the turns ratio, and the ability to provide multiple outputs. However, there are non-isolated topologies (without transformers) such as the buck and the boost converters, where the power processing is achieved by inductive energy transfer alone. All of the more complex arrangements are based on these non-isolated types.ON Semiconductor has been a key supplier of semiconductor products for switching power supplies since we introduced bipolar power transistors and rectifiers designed specifically for switchingEfficient conversion of electrical power is becoming a primary concern to companies and to society as a whole. Switching power supplies offer not only higher efficiencies but also offer greater flexibility to the designer. Recent advances in semiconductor, magnetic and passive technologies make the switching power supply an ever more popular choice in the power conversion arena today.Historically, the linear regulator was the primary method of creating a regulated output voltage. It operates by reducing a higher input voltage down to the lower output voltage by linearly controlling the conductivity of a series pass power device in response to changes in its load. This results in a large voltage being placed across the pass unit with the load current flowing through it. This headroom loss causes the linear regulator to only be 30 to 50 percent efficient. That means that for each watt delivered to the load, at least a watt has to be dissipated in heat. The cost of the heatsink actually makes the linear regulator uneconomical above 10 watts for small applications. Below that point, however, they are cost effective in step-down applications. The switching regulator operates the power devices in the full-on and cutoff states. This then results in either large currents being passed through the power devices with a low “on” voltage or no current flowing with high voltage across the device. This results in a much lower power being dissipated within the supply. The average switching power supply exhibits efficiencies of between 70 to 90 percent, regardless of the input voltage. Higher levels of integration have driven the cost of switching power supplies downward which makes it an attractive choice for output powers greater than 10 watts or where multiple outputs are desired.A topology is the arrangement of the power devices and their magnetic elements. Each topology has its own merits within certain applications. Some of the factors which determine the suitability of a particular topology to a certain application are:1) Is the topology electrically isolated from the input to the output or not.2) How much of the input voltage is placed across the inductor or transformer.3) What is the peak current flowing through the power semiconductors.4) Are multiple outputs required.5) How much voltage appears across the power semiconductors.The first choice that faces the designer is whether to have input to output transformer isolation. Non-isolated switching power supplies are typically used for board-level regulation where a dielectric barrier is provided elsewhere within the system. Non-isolated topologies should also be used where the possibility of a failure does not connect the input power source to the fragile load circuitry. Transformer isolation should be used in all other situations. Associated with that is the need for multiple output voltages. Transformers provide an easy method for adding additional output voltages to the switching power supply. The companies building their own power systems are leaning toward transformer isolation in as many power supplies as possible since it prevents a domino effect during failure conditions. The remainder of the factors involves how much stress the power semiconductors are being subjected to. The differences between the various topologies used within switching power supplies. The transformer-isolated topologies are typically used within the power industry at various power and voltage levels. At reduced DC input voltages and at higher powers, the peak currents that must be sustained by the power switch grow higher which then affects the stress they must endure. The various areas show which topology best fits within that range of input voltage and output power that exhibits the least amount of stress on the power semiconductors.The present day power supplies use a capacitive input filter when powered from the AC power line. A resulting shortcoming is that the AC line is rectified which results in high peak currents at the crests of the AC voltage. These peak currents are typically three to five times higher than the average current drawn by the power supply. This causes excessive voltage drop in the wiring and imbalance problems in the three phase delivery system. Also the full energy potential of the AC line is not utilized.The task is to increase the conduction angle of the AC rectifiers and to make the resulting current waveform look as sinusoidal and in phase with the voltage waveform as possible. In this way, the power drawn by the power supply from the line is maximized for real power. A popular method of accomplishing this is by using a boost converter prior to the actual power supply. Boost-mode supplies exhibit the largest input dynamic range of all the switching power supply topologies. Input voltages down to 30 volts can be boosted to 370 volts on its output (higher than the highest expected peak operating AC crest voltage). The bulk input filter capacitor is now placed on the output of the boost converter. The input capacitor, just following the 50/60 Hz rectifier bridge is now less than 1 uF. This produces an input voltage waveform to the PFC circuit that has a high level of ripple voltage and the boost converter draws its power directly from the line. The semiconductors within a power factor correction stage have some special requirements. First, the 50/60 Hz rectifiers now have to be ultrafast rectifiers, since fast current pulses are being drawn through them. The boost output rectifier will have to be ultrafast if the boost converter is operating in the continuous-mode. The power switch has to clear the diodes reverse recovery charge. In the discontinuous-mode (Pin 200 watts), the output rectifier need not be ultrafast since there is no current flowing through the diode prior to the power switch turning on.开关模式中功率半导体的应用电能通常不会用在其生产或分布的形式。几乎所有的电子系统需要某种形式的能量转换。通过电路把电能从一个特定源转移到一个特定负载所用的设备称作为电源。电源装置(PSU)的典型应用是将交流电转换成电子设备所需直流电。如今在电源装置，能量流通过不间断高频半导体开关来控制。这种装置被称为开关电源。与线性电源相比，他们能提供更大的效率，因为开关可以低损耗地控制能量：当开关关闭时，它会阻止电压和电流的流动，在两种状态中均比较低。同时，开关电源的尺寸较小，重量较轻，从而减少了无源元件的尺寸，降低了热量的产生。小型化倾向的行业，随着半导体技术的发展进步，同时各种能量效率的控制使得“开关” 得到了全方位的应用，在压力-状态-响应中占主导地位。大部分的切换开关早就了今天包括PFC前端末端在内的交流输入的应用。电源供应器出现在70年代中期。我们把这些定义为开关模式产品。开关电源的设计采用了安森美半导体元件，因此直接的称之为开关电源或SMPS。 一情况下，开关电源根据输入和输出波形可分为四种类型： 交流输入，直流输出：整流器，离线转换器输入级 直流输入，直流输出：电压转换器，或电流转换器，或直流到直流转换器 交流输入，交流输出：变频器，交交变频，变压器 直流输入，交流输出：逆变器多年来，电源设计的世界见证了从线性电源的应用逐步走向更实用的开关模式电源(SMPS)的发展过程。线性电源包含一个电源变压器和耗散系列稳压器。这意味着供应器有着非常大且沉重的50/60赫兹变压器，同时，能量转换效率非常的低，两者都是严重的缺陷。30的典型效率是线性的标准关系。相比较70至80的效率，目前可使用开关电源设计。 此外，通过采用高开关频率，电力变压器的大小和开关电源中相关的滤波组件大大减少了比较线性。例如，一个开关电源在20 kHz的条件下工作，所产生的元件尺寸减少了4倍，使得增加了约8倍，在100千赫或者以上。这意味着开关电源的设计可以产生非常紧凑和轻重量的供应。这是现在大部分电子系统的基本要求。供应必须插入到电子系统设计师为它留下的不断缩小的空间。 转换器的核心是高频逆变器部分，高频逆变器的输入电源在极高的频率下切换(使用现有技术20 to 200kHz)，然后过滤，产生平滑的直流输出。可以决定如何转移能量的电路结构被称为开关电源拓扑结构，这是设计过程中极其重要的组成部分。拓扑的组成包括一个变压器，电感，电容和功率半导体元件。 规律的输出提供了一个稳定的在控制/反馈块进行的直流电源。一般而言，大多数开关电源系统运行在固定频率的脉冲宽度调制的基础上，电源开关驱动器的时间范围在一个循环周期的基础上是不尽相同的。这个办法弥补了输入电源和输出负载产生的变化。把输出电压与准确的参考供应进行比较，由比较所产生的误差电压，可使用专门的控制逻辑来终止在正确实例中主电源开关的驱动器脉冲。正确的设计，将能提供一个非常稳定的AC输出供应。 在大多数应用中，开关电源拓扑结构包含一个电源变压器。电源变压器提供隔离，电压通过转率缩放，并能提供多种输出电压。当然，也有非隔离拓扑(没有变压器)，例如降压和升压转换器，功率处理通过感性能量的单独转移达到。所有更复杂的安排，都是以这些非隔离类型作为基础的。 自从我们引进双极功率晶体管和专门设计的开关整流器以来，安森美半导体一直是开关电源的半导体产品的主要供应商。 高效的电力转换正逐渐成为公司乃至整个社会首要关注的话题。开关电源不仅提供更高的效率，并为设计者提供了更大的灵活性。半导体的最新发展，磁和无源技术，使得开关电源在如今的电源转换舞台上日益成为更加普遍的选择。 历史上，线性稳压器是产生稳定输出电压的主要方法。通过线性控制针对其负载变化的一系列功率器件的导电，从而减少较高的输入电压降低到较低的输出电压，进而使得线性稳压器得以运行。这导致一个大的电压被放置在整个传递单位，同时伴随着负载电流流过传递单位。这种余量亏损导致线性稳压器只有百分之三十至五十的效率。这意味着每传递给负载一瓦功率，至少每瓦在热上都