Basics of Noise Countermeasures in Switching Power Supplies

In the previous section, we explained four steps in procedures to address noise. From here on, we further elaborate on the fourth of these steps, “add filters or other components to address the noise”.

Basics of Noise Countermeasures in Switching Power Supplies

Up to this point, we have explained basic topics related to differential (normal) mode noise and common mode noise as well as crosstalk. The following diagram summarizes these types of noise and basic measures to address them.

In order to reduce differential mode noise (shown in blue), in addition to decreasing the area of the loops of large-current paths on the circuit board, optimized decoupling and an input filter are added. It is important that differential mode noise, which is a noise source, be suppressed insofar as possible, and this also results in reduction of common mode noise.

On the other hand, methods to reduce common mode noise (shown in red) include shortening wires to suppress crosstalk, and interrupting common mode paths (increasing the impedance).

Hereafter we will explain in order the addition of filters (input filters and common mode filters), and decoupling, indicated by red characters in the figure.