Common mode choke core is often used to filter common mode emi signal in switching power supply of computer.In the design of the card, the common mode choke core also ACTS as EMI filter to restrain the electromagnetic wave generated by the high-speed signal line from radiating outward.
Filter circuit of common mode choke core, La and Lb are common mode inductance coils.The two coils are wound on the same core with the same number of turns and phase.In this way, when the normal current in the circuit flows through the common mode inductance, the current in the inductance coil wound in the same phase will generate an opposing magnetic field and offset each other. At this time, the normal signal current is mainly affected by the coil resistance (and a small amount of damping caused by leakage inductance).When there is a common mode current flowing through the coil, due to the common mode current's homogeneity, it will generate a magnetic field in the same direction in the coil and increase the inductance of the coil, making the coil behave as a high impedance and generate a strong damping effect, so as to attenuate the common mode current and achieve the purpose of filtering.
High initial magnetic conductivity (this is the common mode choke core basic requirements), high saturation magnetic induction intensity, the temperature is stable compared to the ferrite (can be understood as the temperature rise is small), the frequency characteristics are more flexible, because the magnetic conductivity is high, very small can make a large amount of inductance, adapt to a wide frequency.
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