Are you all familiar with methods such as using filtering capacitors, common-mode inductors, and ferrite beads to eliminate electromagnetic interference 2

The biggest weakness of through-hole capacitors is their fear of high temperatures and temperature shocks, which poses great difficulties when welding them onto metal panels. Many capacitors are damaged during the welding process. Especially when a large number of through-hole capacitors need to be installed on the panel, it is difficult to repair any damage as removing the damaged capacitor can cause damage to adjacent capacitors.

02 Common mode inductance

Due to the fact that most of the problems faced by EMC are common mode interference, common mode inductors are also one of the powerful components we commonly use. Common mode inductor is a common mode interference suppression device with ferrite as the magnetic core. It consists of two coils of the same size and number of turns symmetrically wound around the same ferrite ring magnetic core, forming a four terminal device. It has the function of suppressing large inductance for common mode signals and has little effect on small leakage inductance for differential mode signals.

The principle is that when a common mode current flows through the magnetic ring, the magnetic flux in the magnetic ring overlaps with each other, thus having a considerable inductance and suppressing the common mode current. When two coils flow through a differential mode current, the magnetic flux in the magnetic ring cancels each other out, and there is almost no inductance, so the differential mode current can pass through without attenuation. Therefore, common mode inductors can effectively suppress common mode interference signals in balanced circuits, without affecting the normal transmission of differential mode signals in the circuit.  diode

Common mode inductors should meet the following requirements during production:

(1) The wires wound on the coil core should be insulated from each other to ensure that there is no breakdown or short circuit between the turns of the coil under instantaneous overvoltage;

(2) When a large instantaneous current flows through the coil, the magnetic core should not saturate;

(3) The magnetic core in the coil should be insulated from the coil to prevent breakdown between the two under transient overvoltage;

(4) The coil should be wound in a single layer as much as possible, which can reduce the parasitic capacitance of the coil and enhance its ability to withstand transient overvoltages.

Normally, it is important to select the frequency band for the desired filtering. The larger the common mode impedance, the better. Therefore, when choosing a common mode inductor, we need to refer to the device information and mainly choose based on the impedance frequency curve.

In addition, when choosing, pay attention to the impact of differential mode impedance on the signal, mainly focusing on differential mode impedance, and paying special attention to high-speed ports.diode

03 Magnetic beads

In the EMC design process of product digital circuits, we often use magnetic beads. Ferrite materials are iron magnesium alloys or iron nickel alloys, which have high magnetic permeability and can minimize the capacitance generated between the coil windings of inductors at high frequencies and high resistances. Ferrite materials are typically used at high frequencies because they mainly exhibit inductive characteristics at low frequencies, resulting in minimal losses on the wire. At high frequencies, they mainly exhibit reactive characteristics and change with frequency. In practical applications, ferrite materials are used as high-frequency attenuators for RF circuits.diode