For how to choose SMD magnetic beads for power cord products, we must first know the operating frequency of the switching power supply. Usually most switching power supplies work at hundreds of KHz, and a few can work at several MHz. This frequency is basically in the frequency range of conducted radiation. For the radiation frequency starting at 30MHz, it belongs to the low frequency range. Generally speaking, the radiated EMI noise generated by the power supply is usually in the range of less than 100MHz-300MHz. Therefore, choose the low frequency type magnetic beads with peak frequency less than 300MHz for SMD beads.
Secondly, it is necessary to know the operating current of the power supply. For the magnetic beads that are placed on the switch or non-DC signal, it is usually necessary to convert the effective value of the AC signal to select the rated current of the SMD magnetic beads. Regarding the size of the magnetic beads used in the power cord, as we mentioned earlier, in the case of meeting the design requirements of the layout space, it is necessary to use large-size SMD beads as much as possible.