What is the use of transformer shielded grounding in switching power supply?
Transformer plus shielding is to prevent electromagnetic interference. Because switching power supply switching frequency is very high, the transformer is a source of interference, shielding it to prevent interference with other components.
In principle, the external shield is not required to ground. Grounding are do not know the principle. According to gourd painting scoop.
Internal shielding: between the primary side and the secondary side to increase the winding or copper foil, leads to one end of the original side of the work above the main purpose is to the primary side of the common mode interference signal through the shield back to the source of harassment, if not the shield Layer, there is a common mode interference signal will be passed between the primary winding between the interlayer capacitance to the secondary side, causing the output of the EMI problem.
External shielding: in the transformer outside the magnetic core and winding coated with a layer of copper foil, this layer of copper foil to be closed to form a ring circuit. The leakage magnetic field of the transformer is not closed inside the core, but leaks into the external space. In the high frequency application, the strong leakage magnetic field will induce the voltage in the closed loop of the input and output ports, resulting in EMI test results deteriorate. If there is an external shielding layer, according to the principle of electromagnetic induction, the shield layer will induce the current, the formation of the opposite magnetic field, offset the transformer leakage magnetic field effects.
