外文資料翻譯---開關(guān)模式中功率半導(dǎo)體的應(yīng)用-全文預(yù)覽
【正文】 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 magic 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. Nonisolated switching power supplies are typically used for boardlevel regulation where a dielectric barrier is provided elsewhere within the system. Nonisolated 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 panies 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 transformerisolated 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 shorting 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 acp
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