The impedance of a normal coil consists mostly of the reactance (X) component, but when a ferrite core is used, the resistance (R) component becomes extremely large. The right side of Figure 1 shows the impedance characteristics of a coil with conducting wires passed through a ferrite core. (This is called "hysteresis loss.") As a result, part of the noise current passing through the conducting wires is lost as magnetic loss, reducing the energy. At this time, not all of the magnetic flux energy is returned to current energy, and some is lost as magnetic loss. However, when the current changes, this magnetic flux is converted back into current by electromagnetic induction. When current flows to an inductor comprising a ferrite core, magnetic flux is generated in the ferrite core, and the current energy is converted into magnetic energy. Furthermore, the use of a ferrite core also provides an additional effect. Therefore, the coil functions as a low-pass filter that blocks high-frequency current, enabling attenuation of high-frequency noise. This coil (inductor) is based on the same principle as that of an electronic part inductor, so the impedance increases together with the frequency as shown in Figure 1. By passing conducting wires through the hole of the ring, the conducting wires and the ferrite core form a coil (inductor). įerrite cores come in various shapes, but most are ring-shaped. For these and other reasons, Ni-Zn ferrite is often used for noise countermeasures. Mn-Zn ferrite is conductive, so it requires insulation work, and Ni-Zn ferrite has better high-frequency characteristics. Formerly, coils were often made by winding conducting wires around a ring-shaped ferrite core, so ferrite used for noise countermeasures is likewise called a ferrite core.įerrites include Mn-Zn ferrite and Ni-Zn ferrite according to the composition. įerrite cores are ceramic magnetic bodies consisting of ferrites (soft ferrites) processed into various shapes.
When the delivery date is near, there is no time to change the board, so parts such as ferrite cores that enable countermeasures without changing the board come in handy. There is no problem as long as the noise level is within the regulation value as expected at this point, but the test results sometimes exceed the regulation value. Recently, experience concerning designs that do not emit noise is increasing, and various measures are being implemented beforehand to prevent the generation of noise, but of course the effects cannot be known until the final test. However, the final check cannot be performed until the device design is complete. (Although they are sometimes fixed to the board.)Īs previously introduced, when commercializing an electronic device, it is necessary to check that the noise emitted from the device satisfies the EMI regulations. This time we introduce noise countermeasure parts that do not require mounting on a board. Previously, we introduced noise countermeasure parts mounted on a board as part of the electronic circuit. Noise Suppression Filter Guide Basics of noise countermeasures Ferrite Cores