Analysis of magnetic bead grounding

    The unit of inductance is Xiang, and the model is also named based on the inductance value. For example, GZ2012-100 refers to the inductance packaged with 10uH in 2012 (0805); The unit of magnetic beads is ohms. Generally, the model of magnetic beads is named after the resistance value at 100MHz. It should be noted that this is the resistance value, not the equivalent inductance. For example, JCB201209-301 refers to a magnetic bead with a resistance of 300 ohms when packaged at 100MHz in 2012 (0805).

    Magnetic beads themselves are theoretically energy consuming components, while inductors are theoretically non energy consuming. This is the biggest theoretical difference between the two types of components. The magnetic material of the inductor is not enclosed, and the typical structure is a magnetic rod. Part of the magnetic field line passes through the magnetic material (magnetic rod), and another part is in the air; The magnetic material of the magnetic bead is closed, and the typical structure is the magnetic ring. Almost all Almost all are in the magnetic ring, and will not be emitted into the air. The magnetic field intensity in the magnetic ring constantly changes, inducing current in the magnetic material. Choosing magnetic materials with high hysteresis coefficient and low resistivity can convert these high-frequency energy into thermal energy, which is then consumed. On the contrary, inductance should be selected with low hysteresis coefficient and high resistivity magnetic materials to achieve consistent inductance values throughout the entire frequency band as much as possible. So, the differences in structure and magnetic materials determine the essential differences between magnetic beads and inductors.

    Inductors are mainly used in switching power supplies, resonance, impedance matching, and special filtering, while magnetic beads are mainly used to prevent radiation and improve EMC much better than inductors.

    The magnetic beads consume high-frequency signals and there is no external "magnetic leakage", while the inductance, due to the unclosed magnetic material, will transmit a large amount of high-frequency signals to the external space, causing EMI problems

    Magnetic beads are usually recommended for use on power or signal lines to enhance decoupling effects, but caution must be exercised when using them between ground, especially in applications where high energy interference signals may flow through the magnetic beads.

    I remember when I first learned DSP design, my master recommended a circuit for the DSP simulation application, which is to string two magnetic beads on a digital power supply and an analog power supply, and then add a filter capacitor to it. For a long time, it was regarded as a classic, and it was not until I came into contact with EMC design that I realized how much was wrong and understood the crux of some of the problems at that time.

    The magnetic bead exhibits resistance characteristics when interfering with the passage of current. At this time, there will be a large △ V on both sides of the magnetic bead, which is reflected in the analog part of the DSP. A/D measurement will experience a large fluctuation. No matter what filtering algorithm you use, under continuous interference, the measurement results will definitely be a mess.

    So in these simple applications, it is important not to add magnetic beads on the ground and simply short connect them directly.