EMI Design Based on a Switching Power Supply Device
Usually, the processing process of simulation software for engineering problems such as EMC/EMI is "modeling>reproducing problems>improving design". However, the EMC/EMI problem has the characteristics of randomness and variability, making it difficult to fully replicate an actual engineering EMC/EMI problem. Ansoft's "top-down" EMC solution can easily solve this problem. If you are struggling with EMC/EMI related issues in automotive electronics design, switching power supply design, system design, or device design, this series of articles will analyze engineering examples to help you solve these problems.
Rockwell applied Ansoft design process for EMI design of one of its switching power supply devices
1. Use Q3D to extract parasitic parameters from the PCB layout of the switching power supply.
2. Build a virtual testing platform for conducting interference simulation in Simplorer. The physical part of Figure 10 shows the circuit used for actual measurement of conducted emissions from a switching power supply, including a DC power supply, a linear impedance stable network (LISN), and the tested switching power supply board. The following is the schematic diagram of a virtual testing platform built in Simplorer, with the blue part using the layout parasitic parameter model extracted from Q3D.
3. The time-domain waveforms of common mode and differential mode interference voltages output by the LISN network obtained through Simplorer simulation, and the frequency spectrum of common mode and differential mode EMI in the range of 150KHz~30MHz obtained through FFT transformation, are the comparison between the simulation results and the measured results. The black line represents the simulation results and the red line represents the measured results, which have good consistency.
4. With the help of the Simplorer simulation platform, designers can conduct thorough "what if" research on the performance of device prototypes before processing and testing them, and quickly validate their design ideas on the virtual testing platform provided by the software. Figure 12 shows the conducted EMI simulation results after improving the initial design. The black line represents the initial simulation results, the yellow line represents the simulation results with EMI filtering, the red line represents the conducted EMI simulation results with EMI filtering and XFMR shielding, and the green and blue lines represent the requirements for conducted EMI in the CISPRA and CISPRB standards, respectively.
