The new electric shielding scheme with comb-shaped wire and its applications in SMPS

Common-mode conduction EMI is a key consideration in switch-mode power supplies. Copper foil electric field shielding is commonly used in the SMPS to shield the transformers or inductors in order to reduce the CM conduction interference. However, the copper foil in the magnetic components not only shield the electric field, but also affect the magnetic field distributions due to high-frequency eddy current effects, resulting in extra eddy current losses in the foil and the change of magnetic parameter of the magnetic components. This paper analyzed these behaviors with copper foil shielding and proposed the new shielding scheme which has good electric field shielding effect, but with no effect on the magnetic field. The new shielding media used comb-shaped wire array to form the shielding sheet, instead of traditional complete copper foil. With the new shielding sheet, the eddy current effect due to AC magnetic field can be avoided. The electric field shielding behaviors with the new shielding scheme was deeply analyzed with different wire densities and compared with traditional copper foil shielding. Finally, the application example of the electric shielding for LLC transformer was demonstrated.