基于“负参数”理论的EMI滤波器寄生参数的双重消除

EMI滤波器是抑制传导电磁干扰的有效器件,但分立元件的自有寄生参数对其高频段性能有重要影响。本文利用两个同侧耦合电感器等效出"负电感"和在电感器中心处连接电容器等效出"负电容"的方法,消除滤波器中的寄生电感和寄生电容。为有效控制二次寄生参数对消除效果的影响,设计了一种新型平面"消除器"和双线并绕串联结构的电感器,其中前者为上、下交错排列的PCB导线构成的圆形线圈,采用3D有限元法计算了两交错线圈的互感,为设计该类消除器提供了一种数值计算方法;后者通过高耦合度的线圈中间节点与地之间接一4倍于寄生电容的电容器,可有效消除电感器的一次及二次寄生电容。将此类具有消除器的元件应用于EMI共模滤波器,以此消除对应的寄生参数,实验表明滤波器的高频性能得到了明显改善。

Dual-Cancellation of Parasitic Parameters Based on Theorem of Negative Parameters for EMI Filters

The EMI filters are important components to suppress interference,the high-frequency performance of which suffers from the parasitic parameters of discrete components.The parasitic parameters can be cancelled with the methods of negative parameters,including negative inductance and capacitance.The negative inductance and capacitance are obtained using two in-plane coupled inductors and inductor linked a capacitor to ground at middle node,respectively.In order to reduce the impact of secondary capacitance effectively,a new type of planar eliminator using PCB windings and the inductor with bifilar windings in series are designed in this paper.The former is a circular coil consisted of PCB wires staggered in the board’s upper and lower levels,and the mutual inductance is calculated by 3D finite element model,which provides a numerical method for the design of such eliminator;the latter is achieved through a capacitor connected between the ground and the intermediate nodes of coil which coupling coefficient is closed to one.If a capacitor whose value is times parasitic capacitance is linked to ground at middle node with high coupled winding,the first and secondary parasitic capacitance of inductor can be eliminated effectively.Finally,such planar eliminator and the inductor with bifilar windings in series for parasitic parameters cancellations are applied to the EMI common filters and applicable design rules are established and experimentally validated.