[muRata] EMC Solutions: Noise Suppression Examples

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In switching power supplies, noise filters are installed as shown below to suppress noise being conducted to the AC power supply cable. The capacitor is used as a bypass for noise, and the coil prevents noise conduction to the cable by increasing line impedance.

Noise Emission Status for Switching Power Supplies
Noise Suppression Model for Ordinary Switching Power Supplies

Noise Tendencies in Switching Power Supplies
Examples of Conventional Suppression against Strong Differential Mode Noise
Effective Suppression Methods against Differential Mode Noise using Hybrid Choke Coils
Examples of Confirming the Effectiveness of Hybrid Choke Coils

< References >
Differential Mode Noise and Common Mode Noise
Functions of Respective Noise Filters
Reasons Why Common Mode Choke Coils Contain Differential Mode Inductance

Symbol	Name	Function
L1	Common mode choke coil	Suppresses common mode noise.
CL	Across the line capacitor (X-capacitor)	Suppresses differential mode noise.
CB1 CB2	Line bypass capacitor (Y-capacitor)	Suppresses common mode noise and differential mode noise.

Fig. 1. Noise Suppression Model for Switching Power Supplies