Common Mode Magnetic Ring Inductance
Product introduction: Common mode choke, also known as common mode choke, is often used in computer switching power supplies to filter common mode electromagnetic interference signals. In the board design, the common mode inductor is also used for EMI filtering
Common mode inductance (common mode choke), also known as common mode choke, is a commonly used method of filtering common mode EMI signals in computer switching power supplies. In the design of the circuit board, the common mode inductance also plays a role of EMI filtering to suppress the electromagnetic waves radiated by the high-speed signal line.
Common mode inductance filter circuit, La and LB are common mode inductance coils. The two coils are wound on the same iron core with the same number of turns and phase (reverse winding). In this way, when the normal current in the circuit flows through the common-mode inductor, the current generates a reverse magnetic field in the inductor coils wound in the same phase, which cancel each other out. At this time, the normal signal current is mainly affected by the coil resistance (and a small amount of damping caused by the leakage inductance); when the common mode current flows through the coil, due to the isotropy of the common mode current, a magnetic field in the same direction will be generated in the coil. Increasing the inductive reactance of the coil makes the coil have high impedance characteristics and produces a strong damping effect, thereby attenuating the common mode current and achieving the purpose of filtering.
In fact, if one end of the filter circuit is connected to the interference source, and the other end is connected to the interfered device, La and C1, LB and C2 form two sets of low-pass filters, which can control the common mode EMI signal on the line to a very low level. s level. The circuit can not only suppress the external EMI signal, but also attenuate the EMI signal generated by the circuit itself, effectively reducing the intensity of EMI interference.
Domestic small common mode inductors have the advantages of suppressing high frequency noise, common mode choke coil structure, no signal attenuation, small size, convenient use, good balance, convenient use, and high quality. It is widely used in double-balanced tuning devices, multi-frequency transformers, impedance transformers, balanced and unbalanced transformation transformers, etc.
(1) The wires wound on the core of the coil should be insulated from each other to ensure that the coil does not undergo turn-to-turn breakdown and short-circuit under the action of instantaneous overvoltage;
(2) When a large instantaneous current flows through the coil, the magnetic core should not be saturated;
(3) The magnetic core in the coil should be insulated from the coil to prevent breakdown between the coils under transient overvoltage;
(4) The coil should be wound in a single layer as much as possible, so as to reduce the parasitic capacitance of the coil and improve the ability of the coil to withstand transient overvoltage.
In general, we should also pay attention to selecting the frequency band to be filtered. The larger the common mode impedance, the better. Therefore, when choosing a common mode inductor, you need to look at the device data, mainly based on the impedance frequency curve. In addition, attention should be paid to the effect of differential mode impedance on the signal, especially for high-speed ports.