Filter capacitors, common mode inductor chokes , magnetic beads in the EMC design circuit is a common figure, but also eliminate the three major electromagnetic interference tool. For the role of these three in the circuit, I believe there are many engineers do not know.
Three major tool filter capacitor
Although the resonance of the capacitance is undesirable from the point of view of filtering high frequency noise, the resonance of the capacitance is not always harmful. When the noise frequency to be filtered to determine, you can adjust the capacity of the capacitor, so that the resonance point just fell on the harassment frequency.
Three common-mode tool inductors
Common mode inductor is one of the common components of common-mode inductors. PFC inductors is a ferrite-based common mode interference suppression device, which consists of two identical size , The same number of turns of the coil symmetrically wound on the same ferrite toroid core, the formation of a four-terminal device for the common-mode signal to show a large inductive suppression, and for the differential mode signal shows a small Leakage inductance almost does not work. Principle is to flow through the common-mode current magnetic flux superimposed on each other, which has a considerable amount of inductance, the common-mode current to play an inhibitory effect, and when the two coils through the differential mode current, magnetic By canceling each other, almost no inductance, so the differential mode current can be passed without attenuation. So the common-mode inductance in the balanced circuit can effectively suppress the common-mode interference signal, and the normal transmission line differential signal has no effect.
The three major tool of the beads
In the digital circuit EMC design process, we often use the beads, ferrite material is iron-magnesium alloy or iron-nickel alloy, this material has a high permeability, he can be inductor coil winding between The high-frequency high-impedance case produces the smallest capacitance. Ferrite materials are commonly used in high frequency applications because of their low inductance characteristics at low frequencies, resulting in very little loss in the line. At high frequencies, they are predominantly reactance-characteristic ratios and vary with frequency. In practice, the ferrite material is used as a high-frequency attenuator for RF circuits. In fact, the ferrite is better equivalent to the resistance and inductance in parallel, low-frequency inductance by the short circuit, high-frequency impedance under the impedance becomes very high, so that all the current through the resistor. Ferrite is a consumer device, high-frequency energy in the above into heat, which is determined by the characteristics of his resistance.
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