EMI Filter Design iecainc（EMI滤波器设计iecainc）.pdf

P1: IML/OVY P2: IML/OVY QC: IML/OVY T1: IML MHBD017-03 Sandler MHBD017-Sandler-v4.cls October 6, 2005 18:53 Chapter 3 EMI Filter Design Nearly all power circuits contain an input electromagnetic interference (EMI) filter. The main purpose of the EMI filter is to limit the inter- ference that is conducted or radiated from the power circuit. Excessive conducted or radiated interference can cause erratic behavior in other systems that are in close proximity of, or that share an input source with, the power circuit. If this interference affects the power circuit, it can cause erratic operation, excessive ripple, or degraded regulation, which can lead to system level problems. Input EMI filters may also be used to limit inrush current, reduce conducted susceptibility, and suppress spikes. The specifications for the allowable interference are generally driven by the power circuit specification. The most common specifications include MIL-STD-461 for military applications and FCC for commercial applications. Many other EMI specifications also exist. This chapter will deal with the design and analysis of EMI filters that will reduce conducted interference and conducted susceptibility and limit inrush current. The design of the input filter is slightly more critical when the power circuit is a regulated switching circuit, rather than a linear circuit, because a negative input resistance is created by the regulated switching circuit. Although it is possib