Electromagnetic Interference Generation and Suppression in Switching Power Supplies
The prominent disadvantage of switch mode power supplies is the ability to generate strong electromagnetic interference (EMI). EMI signals have a wide frequency range and a certain amplitude, and after conduction and radiation, they can pollute the electromagnetic environment and cause interference to communication equipment and electronic products. If not handled properly, the switching power supply itself will become an interference source. The impact of electromagnetic interference on the efficiency, performance, and usage of switching power supplies has become an increasingly hot topic of concern. This article analyzes the causes and propagation paths of electromagnetic interference in switch mode power supplies, and proposes effective measures to suppress interference.
Introduction
Electromagnetic compatibility (EMC) is the abbreviation for electromagnetic compatibility in English. It includes two meanings: first, the electromagnetic radiation generated by the equipment during operation must be limited to a certain level; second, the equipment itself must have a certain anti-interference ability, and it must have three elements: interference source, coupling channel, and sensitive body. The switch power supply that supplies power to electronic circuits is of great significance in suppressing interference and ensuring the normal and stable operation of electronic systems. This article proposes effective measures to suppress interference by analyzing the interference sources and coupling channels in switch mode power supplies. And proposed the design and manufacturing methods of switching power supply transformers.
Interference sources and coupling channels in switch mode power supplies
Switching power supplies first rectify AC power into DC power, which is then controlled by switching tubes to become high-frequency. After passing through rectification and filtering circuits, stable DC voltage is obtained, which contains a large amount of harmonic interference. Meanwhile, due to the leakage inductance of the transformer and the peak caused by the reverse recovery current of the output diode, varying degrees of electromagnetic interference will be generated. The interference in switch mode power supplies is mainly concentrated on components with large voltage and current changes (i.e. dv/dt or di/dt), especially switch tubes, output diodes, and high-frequency transformers. Meanwhile, stray capacitance can transmit noise from the power grid to the power supply of the electronic system, causing interference to the operation of electronic circuits. Here we will analyze the causes of several interferences and their coupled paths.
The filtering interference generated by the output rectification and filtering circuit of the switching power supply commonly uses bridge rectification and capacitor filtering circuits at the output end. Due to the nonlinearity of rectifier diodes and the energy storage effect of filtering capacitors, the output current becomes a periodic peak current with a short time and high peak value,. This distorted input current contains not only fundamental components but also abundant higher-order harmonic components.
