A switching power supply is a power supply which maintains a stable output voltage by controlling a ratio of on-to-off time of a switch. The switching power supply products are developing towards a direction of small type and high frequency, which results in difficulties in improvement of EMI noise in switching power supply products. A common mode inductor, as one of main components for suppressing EMI noise in a switching power supply, self characters of which have obvious influence on EMI noise suppression.
As shown in FIG. 1, an equivalent circuit diagram of a common mode inductor is illustrated. As shown in FIG. 2, a schematic structure diagram of a common mode inductor in conventional technologies proposed for improving EMI noise suppression capability of a common mode inductor is shown. The common mode inductor mainly includes a magnetic core 102 and two multilayered coil windings 101 (double-layered coil windings with a first layer coil winding 101A and a second layer coil winding 101B are shown in FIG. 2) symmetrically wrapped around the magnetic core. Furthermore, an isolation gap 103 is formed in each of the multilayered coil windings 101, and the isolation gap 103 is configured to divide, by beginning from a second layer coil winding 101B, each of the multilayered coil windings 101 into two wrapping areas. That is, no isolation gap is formed in a first layer coil winding 101A, and there is an isolation gap formed in the second layer coil winding 101B.
However, the EMI noise suppression capability of this common mode inductor still needs to be enhanced, which hampers the development of switching power supplies towards a direction of small type and high frequency.