Software Method for EMC-Assisted Design of Switching Power Supply Printed Circuit Board

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Software Method for EMC-Assisted Design of Switching Power Supply Printed Circuit Board [Copy link]

To reduce the EMI of electronic equipment, the design of printed circuit boards (PCBs) is the key. A good wiring scheme can reduce the interference level without modifying the circuit topology or adding any components. However, the design of PCBs is currently just an experimental design process that relies on experience in most cases. It is called the "trial & error" design method abroad, which is very blind. The main interference coupling modes on PCBs are conducted interference and near-field interference (including electric field interference and magnetic field interference). They can often be represented by stray resistance, capacitance, and inductance. One of the design goals of PCBs is to try to reduce these stray parameters and reduce unnecessary interference coupling between printed circuits.

　　Many literatures list some methods to reduce stray parameters between printed circuits, but these methods are often too general and still rely heavily on experience in practical applications. At present, there are also auxiliary design software packages that use numerical technology to extract PCB stray parameters and establish simulation models. Although the simulation results can match the measurement results well, this type of method is essentially to transplant the trial & error design method from the hardware platform to the software platform, and cannot guide how to wire to reduce stray parameters between lines. After all, these methods analyze interference from the perspective of centralized circuits, and EMI is essentially a field problem, so there are still considerable limitations.

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Table 1 lists nine different wiring designs and gives the corresponding coupling coefficient and capacitance calculation results. Comparing these results, it can be found that the size, shape and relative position of the printed conductors will affect the coupling coefficient and capacitance between them. In order to more clearly reflect the relationship between the two, the coupling coefficient and capacitance value are plotted in the same figure and linear regression analysis is performed, as shown in Figure 1. The correlation coefficient is 0.98, indicating that the coupling coefficient can well reflect the degree of coupling between the conductors. It is feasible to perform wiring based on the coupling coefficient. Table 1 Coupling coefficient and capacitance value for different wiring designs No. Interference wire and sensitive wire Coupling coefficient Capacitance value (pF) No.1 571.05 8.30×10－3 No.2 482.28 6.58×10－3 No.3 103.31 1.68×10－3 No.4 1535.7 36.5×10－3 No.5 776.35 11.3×10－3 No.6 572.01 8.45×10－3 No.7 1432.9 29.0×10－3 No.8 1003.5 21.0×10－3 No.9 1003.6 21.0×10－3

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The stray parameters of the printed circuit board have a great influence on the EMC of the switching power supply. Appropriate wiring is critical to reducing the interference between printed circuits. By designing the wiring of the PCB according to the interference intensity distribution diagram, sensitive circuits can be placed in areas with weaker interference. Accurate calculation of stray capacitance requires a long calculation time, while the coupling coefficient can display the degree of coupling between wires in real time, greatly shortening the calculation time and assisting wiring design. Both calculation and experimental results have confirmed this. The new software-aided design concept provides new ideas for the design of printed circuit boards.