II。 SOURCE, PATH AND VICTIM OF EMI 

  Undesired voltage or current is called interference and their cause is called interference source。 In this paper a high-speed switching power supply is the source of interference。

  Interference propagated by radiation in area around of an interference source or by conduction through common cabling or wiring connections。 In this study conducted emission is considered only。 Equipment such as computers, receivers, amplifiers, industrial controllers, etc that are exposed to interference corruption are called victims。 The common connections of elements, source lines and cabling provide paths for conducted noise or interference。 Electromagnetic conducted interference has two components as differential mode and common mode [9]。 

A。 Differential mode conducted interference

  This mode is related to the noise that is imposed between different lines of a test circuit by a noise source。 Related current path is shown in Fig。 1 [9]。 The interference source, path impedances,differential mode current and load impedance are also shown in Fig。 1。

B。 Common mode conducted interference 

   Common mode noise or interference could appear and impose between the lines, cables or connections and common ground。 Any leakage current between load and common ground could be modeled by interference voltage source。 

  Fig。 2 demonstrates the common mode interference source, common mode currents I cm1  and I cm2  and the related current paths [9]。 The power electronics converters perform as noise source between lines  of the supply network。 In this study differential mode of conducted interference is particularly important and discussion will be continued considering this mode only。 

III。 ELECTROMAGNETIC COMPATIBILITY REGULATIONS 

  Application of electrical equipment especially static power electronic converters in different equipment is increasing more and more。 As mentioned before, power electronics converters are considered as an important source of electromagnetic interference and have corrupting effects on the electric networks [2]。 High level of pollution resulting from various disturbances reduces the quality of  power in electric networks。 On the other side some residential, commercial and especially medical consumers are so sensitive to power system disturbances including voltage and frequency variations。 The best solution to reduce corruption and improve power quality is complying national or international EMC regulations。 CISPR, IEC, FCC and VDE are among the most famous organizations from Europe, USA and Germany who are responsible for determining and publishing the most important EMC regulations。 IEC and VDE requirement and limitations on conducted emission are shown in Fig。 3 and Fig。 4 [7][9]。

  For different groups of consumers different classes of regulations could be complied。 Class A for common consumers and class B with more hard limitations for special consumers are separated in Fig。 3 and Fig。 4。 Frequency range of limitation is different for IEC and VDE that are 150 kHz up to 30 MHz and 10 kHz up to 30 MHz respectively。 Compliance of regulations is evaluated by comparison of measured or calculated conducted interference level in the mentioned frequency range with the stated requirements in regulations。 In united European community compliance of regulation is mandatory and products must have certified label to show covering of requirements [8]。 摘要：研究了开关直流稳压电源的保护系统,本着保护系统设计的原则和针对系统的保护措施，开展了开关稳压电源中各种保护的特点及其设计方法,在下面介绍了若干特殊的保护电路。 

关键字： 保护电路 系统设计 开关电源

1、引言