The principle of the winding layer of the DC high-frequency transformer shielding layer Does the transformer shielding layer refer to the winding or copper skin and grounding outside the transformer?
The topic we are going to discuss today is the DC power shielding mechanism. I contacted many customer engineers and learned about the EMI problems related to transformers and learned that adding DC shielding would improve EMI, but the specific mechanism is not yet clear. Let me first talk about my own understanding. The principle of DC power transformer shielding is that C5 is the primary and secondary side capacitance of the transformer, which transmits the interference noise measured by the primary to the secondary. In theory, adding a Y capacitor (C4) is the easiest and will not increase additional losses. However, for safety reasons, the leakage current is not very large, so other methods have been proposed.
Principle of DC transformer shielding This connection method divides C1 into two parts. The primary side corresponds to the DC power shield, and the secondary side is shielded. Both sides must be grounded. Yes, it is divided into two capacitors and grounded in the middle. The primary noise of the DC power supply is bypassed, and a metal plate is added on the primary and secondary side to divide the primary and secondary capacitors into two parts. The principle of DC transformer shielding is that the primary noise can be connected to the ground by the metal plate.
Principle of DC power transformer shielding. DC high frequency transformer internal shielding internal shielding and external shielding: add winding or copper foil between the primary side and the secondary side, and connect one end to the working ground of the primary side. The main purpose is to return the common mode interference signal on the primary side to the interference source through the shielding layer. Without this shielding layer, common mode interference signals will be transmitted to the secondary side through the interlayer capacitance between them, and the primary and secondary windings will eventually cause output EMI problems.
External shielding of DC high-frequency transformer: A layer of copper foil is tightly glued to the magnetic core and external windings of the transformer. The copper foil layer must be enclosed in order to form an induction loop. The magnetic field in the leakage inductance core of the transformer is not closed, but leaks to the outside. In high-frequency applications, a strong leakage magnetic field will induce voltage in the closed loop of the input and output ports, resulting in insufficient voltage. EMI test results, if there is an external shielding layer, according to the principle of electromagnetic induction, the shielding will be induced in this layer The electric current forms the opposite magnetic field, thus offsetting the influence of the leakage magnetic field of the transformer.
