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Through circuit integration, modularization, circuit analysis and design, it can be said that it is a comprehensive analysis and design. The EMI scheme research will have a significant impact on the improvement of the performance of electronic equipment in the future. With the increasing popularity of electronic products and the slow understanding of electromagnetic hazards, it has become a major topic in the electronic academic community to reduce EMI interference signals. How to reduce EMI of power module is analyzed below.

According to the specifications of the International Special Committee on Radio Interference or the International Special Committee on Radio Interference or the CISPR Federal Communications Commission (FCC). CISPR specifications generally only cover the standards and limitations of electromagnetic compatibility (EMC) transmission test. Generally speaking, the power module has five shields, effectively including the radiation transmission of adjacent components. However, if the sixth side of the printed circuit board (PC) is not shielded, it is recommended to place the grounding under the converter and transmit it to the shell to control the transmission EMI of the converter.


For example, the power module adopts metal shielding structure, the manufacturer can provide CE and RE data sheet curves, and the base electroplating converter can provide good near-field B radiation maintenance. At most frequencies, the base electroplated converter is about 10 dB quieter than the open frame design/ μ M。

EMI reduction solution analysis:

Voltage regulator, according to the source of transmitted and radiated energy, makes power supply designers carefree. Another way of CE is to make the voltage paths of modules close to each other and parallel. Symmetry is always the best way for CE and EMI to reduce it. There is a ground plane at its bottom, which can be stacked together in many ways. This is similar to the operation with two twisted pairs, which is most suitable for removing common mode noise. Prevent the circuit from operating as an antenna through the large loop. Keep close to the power cord, which will minimize the loop area and keep the RE low.

You may also need to input or export filters externally. If so, the stray inductance and capacitance of the filter must be prevented, otherwise it may cause instability or performance degradation of all power systems.


The resonance frequency is displayed as a filter ω f. Its peak value is positively correlated with the filter damping ratio. Therefore, if its larger impedance is close to the impedance of the power module, the underdamped filter is most likely to cause shock. The resonant frequency derived by the converter is displayed as a filter ω o. All external derived filters will change this. The stable design composition will be to design a filter so that its peak output impedance (resonant frequency of the filter) is ten times or more less than the module derived filter and all external derived filters under the power module input impedance (resonant frequency of the power).

The X capacitor is connected between the line phases and can effectively resist the influence of symmetry (differential mode). Y capacitor is a capacitor from EMI capacitor power supply to shell grounding, which can effectively resist asymmetric effects (common mode). Sometimes, they will also be transmitted from the power output terminal of each converter to chassis grounding.

The advantage of the same power module is that it can clear the shooting frequency formed when two or more devices work close to each other. If we can operate multiple power modules in the same time, all power modules will generate EMC radiation and have similar frequency band density, which makes it easier to filter out special frequencies. Of course, the module power supply must have a SYNCH pin that can use external frequency. Some modules can browse the internal oscillator, and then the oscillator is suitable for driving the SYNCH pins of many modules equipped with master/slave.

Sometimes rotating the power supply module or other magnetic components 90 ° (such as transformers and inductors) can improve the EMI performance of the power supply design. Even subtle design changes will lead to higher EMI of power supply than the necessary EMI. The designer should understand the source of noise and how to reduce the noise to an acceptable level.

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