The Generation and Suppression of Electromagnetic Interference 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.
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.
The core of the switch circuit is also one of the main sources of interference, which is mainly composed of switch tubes and high-frequency transformers. The dv/dt generated by the switching tube has large pulses, a wide frequency band, and abundant harmonics. The main reason for this pulse interference is:
At the moment when the switch tube is turned on, a large surge current is generated in the primary coil of the transformer, and high surge peak voltage appears at both ends of the primary coil; At the moment when the switch is turned off, due to the leakage flux of the primary coil, a portion of the energy is not transmitted from the primary coil to the secondary coil. The energy stored in the leakage inductance will form a decay oscillation with a peak with the inter pole capacitance and resistance of the switch tube itself, which will be superimposed on the turn off voltage of the switch tube, forming a turn off peak voltage. This noise will be transmitted to the input and output terminals, forming conducted interference.
