共模骚扰的成因与对策

Generation and suppression of common-mode disturbance

共模骚扰往往是造成电子电气产品工作失灵或辐射发射测试超标的主要原因。它主要可以分为两种 :一种是侵入设备的共模骚扰 ,另一种是从设备内部辐射出来的共模骚扰。侵入设备的共模骚扰主要由地环路引起 ,因此在设计上采用平衡电路或设法切断地环路可以提高设备的抗干扰性能。设备内的共模骚扰通过连接线向外辐射 ,相当于一副不对称振子天线 ,可以采用共模滤波器或屏蔽电缆等措施。但最根本的应该是在印刷电路板设计、元器件布置和连接线的安排上下功夫 ,抑制共模骚扰源的产生。本文将理论与实例相结合 ,对这两种共模骚扰的成因、表现形式和抑制对策进行了系统的介绍。

Common mode disturbance is always the chief criminal of the working failure of electronic and electric appliances.It can also make the radiated emission test of the appliances over limit.There are two categories of it: one is the common mode disturbance intruding into the equipment;the other is that radiating from the equipment.Applying the balance circuit and cutting the ground loop can choke the former one that mainly caused by ground loop.The latter is emitted through the connecting cables that are equivalent to the asymmetric element antennas.So common mode filters and shielding cables can be used on the 'antennas' to reduce the radiation.But most attention should be put on the PCB design,elements position and line connection, which can suppress the source of the common mode disturbance.This paper deals with a comprehensive and detailed introduction about the classification,cause,behavior and suppression methods of the common mode disturbance combining theory with examples.