EMI propagation process
Time:2022-06-19
Views:2001
Electromagnetic interference is the most common problem in the process of electronic circuit design. Designers have been looking for ways to completely eliminate or reduce electromagnetic interference, that is, EMI. But if you want to completely eliminate EMI interference, the first thing you need is to understand what EMI is and how its propagation process is. This article will give a general introduction to the propagation process of EMI.
EMI is a general term of electromagnetic interference, but actually electromagnetic interference is divided into two types, one is transmitted interference, the other is radiated interference. Conducted interference mainly refers to that the interference signals generated by electronic equipment are transmitted through wires or public power lines to interfere with each other. Further subdivision, conducted interference is divided into common mode interference and differential mode interference.
EMI propagation process
EMI propagation process mainly passes through three parts: interference source, interference path and receiver. For the switching power supply, the last part does not need to be considered, and the interference source cannot be eliminated, because it is also the source of the switching power supply. However, the interference of the interference source can be reduced through soft switching and buffering. Controlling interference is an important part of reducing EMI of switching power supply, and it is also the focus of this paper.
Spectrum generated by signal source waveform
Frequency spectrum generated by voltage waveform
The frequency spectrum of periodic signal has no even harmonics, and the positive and negative symmetrical waveform produces less frequency components, such as bridge circuit. I forgot all the advanced numbers. I‘m interested in doing FFT.
EMI is a general term of electromagnetic interference, but actually electromagnetic interference is divided into two types, one is transmitted interference, the other is radiated interference. Conducted interference mainly refers to that the interference signals generated by electronic equipment are transmitted through wires or public power lines to interfere with each other. Further subdivision, conducted interference is divided into common mode interference and differential mode interference.
EMI propagation process
EMI propagation process mainly passes through three parts: interference source, interference path and receiver. For the switching power supply, the last part does not need to be considered, and the interference source cannot be eliminated, because it is also the source of the switching power supply. However, the interference of the interference source can be reduced through soft switching and buffering. Controlling interference is an important part of reducing EMI of switching power supply, and it is also the focus of this paper.
Spectrum generated by signal source waveform
Frequency spectrum generated by voltage waveform
The frequency spectrum of periodic signal has no even harmonics, and the positive and negative symmetrical waveform produces less frequency components, such as bridge circuit. I forgot all the advanced numbers. I‘m interested in doing FFT.
Effect of duty cycle and waveform slope
When the duty cycle is larger, the interference amplitude is larger, which can be calculated from the FFT coefficient.
The slope of the waveform has a great influence on the high-frequency part of the interference. The low frequency part has little effect. The low-frequency part is mainly determined by the amplitude of the waveform and the width of the high-level part, but the turning point of the large-scale decline of the high-frequency part is 1/ (3.14*tr). Therefore, the higher the TR is, the lower the turning point frequency is, the greater the high-frequency decline is.
Summary:
Both voltage and current waveforms have rich frequency components
When it exceeds 200m, the amplitude is already very low, so the impact is very small
Waveform affects low frequency part
Rising edge and falling edge affect the high frequency part
The duty cycle has a little influence on the spectrum amplitude
It can be seen that the process of electromagnetic interference is not simple, but it is not complicated. Only after fully understanding the force of EMI can EMI be effectively avoided and suppressed. I hope you can have a further understanding of EMI after reading this article.
When the duty cycle is larger, the interference amplitude is larger, which can be calculated from the FFT coefficient.
The slope of the waveform has a great influence on the high-frequency part of the interference. The low frequency part has little effect. The low-frequency part is mainly determined by the amplitude of the waveform and the width of the high-level part, but the turning point of the large-scale decline of the high-frequency part is 1/ (3.14*tr). Therefore, the higher the TR is, the lower the turning point frequency is, the greater the high-frequency decline is.
So we should think of measures to reduce the slope, buffer circuit.
Summary:
Both voltage and current waveforms have rich frequency components
When it exceeds 200m, the amplitude is already very low, so the impact is very small
Waveform affects low frequency part
Rising edge and falling edge affect the high frequency part
The duty cycle has a little influence on the spectrum amplitude
It can be seen that the process of electromagnetic interference is not simple, but it is not complicated. Only after fully understanding the force of EMI can EMI be effectively avoided and suppressed. I hope you can have a further understanding of EMI after reading this article.
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