Common-mode inductor resistor filter circuit 1

The common-mode inductor is inserted between the transmission conductors to simultaneously suppress high-frequency common-mode noise on each conductor relative to ground. The conventional approach involves winding two identical coils around the same ferrite ring. The ferrite exhibits low magnetic loss, and the winding method ensures that the magnetic flux in the ring overlaps when common-mode current flows through both coils, resulting in significant inductance to suppress the common-mode current. Conversely, when differential-mode current flows through the two coils, the magnetic flux in the ring cancels out, yielding minimal inductance, diode allowing the differential-mode current to pass without attenuation, as shown in Figure 4-33. Essentially, the common-mode inductor functions as a bidirectional filter: it filters out common-mode electromagnetic interference from signal lines while also suppressing its own electromagnetic emissions to prevent interference with other electronic devices operating in the same electromagnetic environment.  Filter Circuit  In EMC design, since the primary function of filtering is to attenuate high-frequency noise, filters are typically designed as low-pass filters.  1. Resistor Filter Circuit  The RC π-type filter circuit essentially adds an additional RC filter stage to the capacitor filter. If S represents the ripple factor of the voltage across C, then the ripple factor S at the output voltage is given by S = (1 / ∞C2) - So. Analysis reveals that resistor R serves to drop the residual ripple voltage across its terminals, which is then bypassed by C2.diode